Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).
|Date: Tuesday, 21/June/2022|
|7:15am - 8:15am||Breakfast|
Location: Ballroom AB
|7:15am - 8:15am||Authors' Breakfast|
|8:00am - 8:30am||IPMHVC Magna Stangenese Memorial|
Location: Ballroom EF
|9:30am - 10:00am||Coffee Break|
Location: Ballroom AB
|10:00am - 12:00pm||Plasmas, Discharges, and Electromagnetic Phenomena|
Location: Ballroom C
Session Chair: Mona Ghassemi, Virginia Tech
10:00am - 10:20am
Plasmas and Discharges: 1
Computational study of plasma flow in arcing horns during a voltage surge
1Esgee Technologies Inc., United States of America; 2The University of Texas at Austin
Arcing horns are used to protect the insulators from high-electric stress conditions. These horns maintain a certain gap between the horn tip such that under excess voltage conditions, the air between the horns breaks down prior to any flashover event across the bushing. Subsequent to the breakdown, a conductive plasma channel forms between the arcing horns. This arc formation leads to the parallel current path which avoids the high voltage build-up across the insulator. In this study, we use VizSpark, a high-fidelity plasma flow solver, to simulate the arcing between the horns under over-voltage conditions. The horn geometry is taken from the previously reported research literature. The build-up of potential in the horns and subsequent arcing in between the electrodes is reported with detailed information on the electric field. The potential and electric field distribution inside the insulator is also reported.
10:20am - 10:40am
Plasmas and Discharges: 2
Numerical simulation of arcing during contact separation in SF6-filled high voltage circuit breaker
1Esgee Technologies Inc., United States of America; 2The University of Texas at Austin
The numerical simulation of thermal arcs in circuit breakers has been challenging, essentially due to the multi-physics involved in the process. In this work, we use VizSpark, a fully-coupled electromagnetic and fluid flow solver to simulate the arcing inside the SF6-filled circuit breaker. The two-dimensional axisymmetric mesh is created for a plug-tulip type SF6 breaker geometry widely reported in the research literature. The moving plug is simulated as an in-motion subdomain, while the tulip, auxiliary nozzle and main nozzle are considered to be static. The sinusoidal current amplitude is varied from 4 to 40 kA to simulate the arcing during the disconnection process. We discuss the temperature, velocity and pressure maps at different time instants to demonstrate the arc evolution process until it quenches.
10:40am - 11:00am
Plasmas and Discharges: 3
Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing, China, China, People's Republic of
To investigate the evolution of electron density of pin to plate discharge plasma at atmospheric pressure, the atomic optical emission line is processed by the interpolation to reduce the uncertainties of the Stark broadening method at first. Based on the Stark broadening method and the imaging method, the electron density of the plasma generated at different pulse frequencies, gap distances and inner diameters of the electrodes is diagnosed. The experimental results indicate that reducing the pulse frequency, shortening the gap distance of the electrodes and using thinner diameter electrode are all in favor to enhance the electron density. With the help of the global model, we perform the numerical simulation to explore the factors that influence the variation of the electron density. According to the simulations results, we find the reduced discharge volume results in the increase of electron density at low pulse frequency. When the gap distance of the electrodes is reduced, although the increased absorbed power and the reduced discharge volume both have an effect on the electron density, the reduced discharge volume plays a decisive role between these two factors. Moreover, using thinner inner diameter electrode can also reduce the discharge volume, which is beneficial to obtain the plasma with high electron density.
11:00am - 11:20am
Plasmas and Discharges: 4
Pulsed Spark Plasma Cracking Heavy Oil for Hydrogen and Acetylene Production
1Beijing International S&T Cooperation Base for Plasma Science and Energy Conversion, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China; 2University of Chinese Academy of Sciences, Beijing 100049, China
Spark discharge plasma is a promising technology for heavy hydrocarbons cracking due to its wide feedstocks adaptability and high conversion rate. Pulsed discharge can improve energy efficiency in energy conversion by its unique low energy compression and high instant power release. A combination of spark plasma and pulsed discharge has a potential for cracking the abundant but low-quality heavy oil efficiently into valuable light chemicals, such as hydrogen and acetylene. In this work, we used microsecond pulse power to crack heavy oil, and the spark discharge and conversion characteristics were studied in a gas-liquid reactor without catalyst at atmosphere pressure and room temperature. Heavy oil was injected into the plasma reaction area by a hollow needle electrode to improve contact with the plasma. Pulse voltage, pulse frequency and carrier gas sorts were evaluated for the improvement of discharge stability and conversion. Hydrogen and acetylene were the main gaseous products, and the gaseous products flow rates increased with discharge proceeding and became stable after 90 s. High voltage and high frequency can improved spark discharge stability, and with the increase of discharge power, the hydrogen and acetylene production flow rates were increased. Gaseous products flow rates were more superior than DBD (dielectric barrier discharge) and corona discharge. Conversion experiments in different carrier gases indicated that methane atmosphere was favorable for heavy oil cracking to produce more gaseous products. The spark discharge emission spectra in heavy oil mainly consisted of C2 and Hα, and the gas temperature was estimated at about 3000 K by fitting C2 spectra lines. This work provides a new idea for heavy oil utilization.
11:20am - 11:40am
Plasmas and Discharges: 5
1Nagaoka University of Technology, Japan; 2Pulsed Power Japan Laboratory Ltd.
As one of the industrial applications by pulsed power, water purification and sterilization by pulsed electric discharge with water has been investigated. Pulsed power discharge in water produces OH radical and shockwave which decompose harmful substances and kill bacteria. For these applications, it is important to study electric breakdown in water. In a previous study, we confirmed experimentally that a pre-electric field makes a main electric field required for arc-discharge decrease for a few hundred micro-second. From these results, new questions have come up, that is, how the effects of pre-fields on a streamer discharge and production of active species are. Thus, we investigated the effects experimentally. The streamer discharge was generated at a point-to-plate electrode in water, applying a pre-voltage and a main voltage using a pulse transformer source consisting of LTD boards and cores. Characteristics of the streamer discharge with various peaks of the pre-voltage and with various times between the pre-voltage and the main-voltage, were investigated from obtained voltage and current waveforms. Then, the amounts of hydrogen peroxide produced by the electric discharge with and without the pre-electric-field were measured and compared to investigate the effects on active species. In this presentation, these results are detailed, and the effects of the pre-electric field on the generation of streamer discharge and active species are discussed.
11:40am - 12:00pm
Plasmas and Discharges: 6
Underwater Electric Discharges: Experiment and Modeling
1Loughborough University, United Kingdom; 2University of Pau, France
At present, underwater electric pulsed discharges are used in a wide range of modern applications. During the development of a system for generating underwater acoustic pressure pulses, a numerical model is an essential tool for guiding the design and interpreting the data. Developing a complex 1-D numerical code, like those presented in the literature, requires a substantial dedicated effort. Unfortunately, previous work trying to use simple and elegant theoretical models developed many decades ago reported a fundamental issue, apparently related to the input data. The present work performs a detailed analysis of the real meaning of the voltage measured across an underwater discharge and clarifies the correct way the power input to a simple two-phase model should be calculated. Based on accurate measurements, a phenomenological methodology to obtain the input data is demonstrated, with theoretical predictions obtained from the simple two-phase model being successfully compared with the experimental evidence obtained from both the present work as well as from other reliable data presented in the literature.
|10:00am - 12:00pm||Solid State Modulators|
Session Chair: James Randall Cooper, Cooper Consulting Services, Inc.
10:00am - 10:20am
Solid State Modulators: 1
Design and Analysis of a 24 kV PCB-Bus for the Low Impedance Interconnect of a Multiphase PEBB-based Converter
Virginia Tech - Center for Power Electronics Systems, United States of America
In this work, the design and analysis of a medium voltage (MV) printed circuit board (PCB) -based planar power bus rated for 24 kV with distributed capacitor daughtercards is presented. This bus provides the low impedance interconnect between an external power supply input and two phase legs of a 24 kV/2 MW power electronics building block (PEBB) -based multilevel modular converter (MMC). The bus serves as a motherboard for capacitor daughtercards which are rated for 9 µF 3 kV each. Electric field (E-field) analysis and parasitic extraction was performed via finite element analysis (FEA) using COMSOL Multiphysics and Ansys Electromagnetics for board- and system-level integration. Insulation performance for each component and the assembly was verified through partial discharge (PD) analysis using an Omicron MPD600. The motherboard and capacitor daughtercards partial discharge inception voltage (PDIV) were tested on a layer-to-layer basis, in addition to the full assembly to ensure the system was PD free under normal operation.
A single PEBB is a converter in which the power stage and all ancillary circuitry required to operate independently are contained in a single structure. PEBBs may be stacked in a series and/or parallel fashion to achieve a higher voltage and/or current rating respectively. The 24 kV MMC includes four PEBBs in the upper arm and four PEBBs in the lower arm of each of the two phase legs. Each PEBB also has an independent forced air cooling system which is referenced to earth ground (GND). Due to the system’s complexity, the boards layer stackup and connector design were critical when fully integrated into the system.
This 24 kV bus was implemented using a 22-layer stackup with a staggered offset between conductor edges for field grading. A layer of FR4 with a controlled thickness was used between the outermost conductive layer and surface pads. This allowed high fields to be contained with the solid dielectric to avoid corona along the surface of the PCB. Additionally, guard pads were implemented to reduce the E-field intensity in air near terminals. These guard pads are placed directly below device terminals and connected to the same potential, at some height within the bus so the field intensity is reduced.
Eight capacitor daughtercards rated at 9 µF 3 kV each were mounted to the motherboard creating a 1.13 µF 24 kV capacitor bank. The daughtercards were constructed using a series-parallel array of 1.5 kV commercial-off-the-shelf (COTS) capacitors. Using this method, the target capacitance for our specific application was achievable. It was beneficial to avoid bulky high voltage can capacitors which require their cans to referenced somewhere near the voltage of their terminals. Additionally, the array of parallel film capacitors provided a much lower impedance which is desirable for such an interconnect.
The final manuscript will provide background on the 24 kV PEBB-based converter at the heart of this work. Detailed analysis for and design of the 24 kV PCB bus and the 3 kV capacitor daughtercards will be presented. Test methods and more extensive results will also be presented.
10:20am - 10:40am
Solid State Modulators: 2
A 30-kV Solid-State Impedance-Matched Marx Generator: Practical Considerations on Impedance Matching
Eindhoven University of Technology, The Netherlands
Based on the topology of the Impedance-Matched Marx Generator (IMG) presented in 2017 by researchers from Sandia (and others) , we created a solid-state IMG using MOSFET switches . The advantage of using the IMG topology is that by using transmission lines to transmit the pulses from the Marx stages the rise time of the pulses can be maintained at the output waveform (when carefully impedance-matched). By designing the Marx stages very compactly and using fast semiconductor components, adjustable pulses with rise times of just several nanoseconds are feasible with this topology. Since we require such fast rising pulses for transient plasma generation, the solid-state IMG is ideally suited for our purpose. In this contribution we present the development of a 30-kV version of the solid-state IMG. It utilizes 12 stages of gate-boosted  and series-connected 1200V SiC MOSFETs and achieves several ns rise time at 30-kV output voltage. Specifically, we also focus on the practical considerations on impedance matching with a modified, much longer version of the IMG to investigate practical considerations on impedance matching. We will show that if the matching criteria are not observed, severe distortion of the waveform is possible and that for the fastest pulses we need the best matching possible.
 W. A. Stygar et al., “Impedance-matched Marx generators,” Phys. Rev. Accel. Beams, vol. 20, 040402 (2017)
 T. Huiskamp and J. J. van Oorschot, “Fast Pulsed Power Generation with a Solid-State Impedance-Matched Marx Generator: Concept, Design and First Implementation”, IEEE T. Plasma Sci., vol. 47, 4350 - 4360 (2019)
 M Azizi, J. J. van Oorschot, T Huiskamp, “Ultrafast Switching of SiC MOSFETs for High-Voltage Pulsed-Power Circuits”, IEEE Transactions on Plasma Science, vol. 48, 4262 - 4272 (2020)
10:40am - 11:20am
Solid State Modulators: 3
The Stacked Multi-Level Klystron Modulators for the ESS Linac
1European Spallation Source ERIC; 2Lund University Faculty of Engineering - LTH, IEA Division
The European Spallation Source (ESS) Linac will require by its completion a total of 33 klystron modulators. They are based on the novel Stacked Multi-Level topology and are rated at 115kV/4x25A; 3.5ms/14Hz, therefore capable of powering 4 klystrons rated at 1.6MWpk, 704MHz in parallel. Besides complying with the ESS requirements in terms of pulse quality (i.e. rise times0..99% < 120µs; flat-top droop <1%; ripple <0.2%pk-pk), they also comply with relevant power quality standards on the electrical grid (current THD below 5%, unitary power factor, flicker free operation), thanks to the adoption of Active Front End (AFE) rectifiers in conjunction with constant power regulated DC/DC capacitor chargers. These features allow their direct connection to the AC line without the need for external line compensators or filters.
The topology is modular and based on the association in series of 6 identical HV modules, each rated for 20kVpk and formed by a HVHF transformer, a HV diode rectifier bridge and a HV LC low-pass filter. These modules are placed in an oil tank and are driven by a 1kV/15kHz H-bridge inverter, which in turn is fed from a capacitor bank charged by the aforementioned AFE+DC/DC chargers.
The modulators have a footprint of 1.6m x 4m and a weight of 11.5 ton (including oil). The mechanical layout was designed in order to facilitate access to each component for repairing. In particular, the low voltage and high voltage cabinets can be assembled and repaired independently, with the first one directly pluggable into the top of the second one. The high voltage cabinet comprises the complete oil tank assembly and it can be easily extracted from each side of the modulator by using the built in sliding rail system, facilitating access for maintenance purposes and interchangeability of the HV modules.
In a first part of this contribution, an overview of the different blocks and functionalities of the power conversion structure will be addressed. In a second part, the main lessons learned during the design, construction and validation of both the reduced scale prototype and the full scale series units will be presented, together with the implemented corrective actions and their effectiveness. This will include issues related to the design of the HV modules like field control, effect of stray inductances and parasitic capacitances, integration into the oil tank, the reliability of the insulated oil and the impact of their handling procedures, the common mode noise effects and their mitigation, eddy currents mitigation etc. In the third part, experimental results obtained with the first 660kVA rated series modulator powering a HV resistive dummy load and klystron load will be presented and discussed.
A total of 18 series modulators have been delivered to ESS for the completion of phase I of the Linac construction, allowing an average beam power in the target of 2MW. For future power upgrades of the Linac to 5MW, additional 16 units of similar type will be required.
11:20am - 11:40am
Solid State Modulators: 4
Evaluation of Klystron Modulator Performance in Interleaved Pulsing Schemes for the ESS Neutrino Super Beam Project
1Lund University; 2European Spallation Source ERIC
It has been proposed that the relatively low duty cycle of the European Spallation Source (ESS) linac allows acceleration of additional H- ion pulses interleaved with the baseline proton pulses, representing a unique opportunity to construct a neutrino super beam (ESSnuSB) facility of unparalleled luminosity. Coupled with a distant Cherenkov detector, it is believed that evidence of CP violations in leptons could be obtained, representing a significant step towards understanding the matter/antimatter asymmetry.
In this paper, several such interleaved pulsing schemes are considered from the perspective of the klystron modulators and the RF power system in investigating the possibility to realize the ESSnuSB. Conserving the required output RF energy, these pulsing schemes vary in terms of 1) number of added H- ion pulses per baseline cycle, 2) pulse amplitude and 3) pulse length. Each prospective pulsing scheme offers unique advantages while differently impacting klystron modulator performance. Whereas the ESS linac baseline design requires 33 klystron modulators (rated for pulse amplitude 115kV/4x25A, pulse length 3.5ms and pulse repetition rate 14Hz; each modulator powering 4 parallel klystrons rated 1.6MWpk at 704MHz), the proposed upgrade requires doubling the baseline linac average output power and thus either doubling the capacity of existing modulators or the procurement of additional modulator systems.
In order to evaluate and compare the merit of these solutions from a system perspective, a mathematical framework connecting the attributes of the proposed pulsing schemes to the power transfer curves of the klystrons and subsequently to the performance of the klystron modulators is developed. In particular, the impact on modulator-to-beam efficiency, modulator average input power quality, modulator output pulse flat top ripple, total upgrade cost, total operational cost (assuming a life time of 25 years), and required additional system size is assessed.
Two particularly promising interleaved pulsing schemes are evaluated in circuit simulation. It is demonstrated that an upgrade of the existing modulators utilizing the selected pulsing schemes maintains the baseline modulator-to-beam efficiency (>90%) keeping the input power quality and output pulse quality performance intact while representing a cost-effective solution for the linac upgrade to implement the proposed ESSnuSB project.
11:40am - 12:00pm
Solid State Modulators: 5
Analysis of the Triggering Instants of the Solid-State Switches of the Pulsed Power Sources for Achieving Optimal Projectile Velocity in a Multistage Induction Coilgun
Indian Institute of Science, Bangalore, India
A multistage induction coilgun works on the principle of electromagnetic induction between an array of drive coils, which are wound on a long insulating barrel of appropriate length, and an electrically conducting projectile (or armature) placed inside the barrel. Previously charged high voltage capacitor banks are sequentially discharged into the drive coils through high voltage solid-state switches leading to the generation and flow of high magnitude impulse currents through the drive coils. Time-varying magnetic flux thus produced by the pulsed currents through the drive coils interact with the projectile inside and induce a resultant eddy current in it. The electromagnetic thrust (F) exerted on the projectile is a product of the excitation current through the drive coil (ic), induced current on the projectile (ip), and the mutual inductance gradient (dMcp/dx, i.e., the change in mutual inductance between the drive coil and the projectile as the projectile moves along the barrel). The higher the electromagnetic thrust is available from each stage, the higher is the launch velocity (vp) of the projectile that can be achieved after each stage. A higher dMcp/dx leads to a higher F. Now, dMcp/dx essentially depends on the radii of the drive coil and the projectile, and the distance between the midplanes of the drive coil and the projectile, i.e., the triggering instant of the pulsed power source w.r.t. the position of the projectile inside each drive coil. For a particular multistage induction coilgun design, where the radii of the drive coil and the projectile are fixed, the appropriate instant of synchronization of triggering of the stages, i.e., the optimum triggering instant of the solid-state switch of the pulsed power source w.r.t. the position of the projectile inside each drive coil, plays a vital role in achieving a higher vp of the projectile. The several stages of a multistage induction coilgun can typically be energized in two ways: (1) positive-positive (PP), where the direction of the excitation current in the subsequent drive coils is kept the same, and (2) positive-negative (PN), where the direction of the excitation current in the subsequent drive coils is reversed alternatively. The optimum triggering instant for the projectile inside each drive coil of the subsequent stages changes accordingly in these two launching configurations. This paper investigates and compares the difference in triggering instants for the projectile inside each drive coil in PP and PN launcher configurations. The analysis is carried out with a four-stage induction coilgun. The input electrical energy to each stage is kept constant. The triggering instant for the projectile inside each drive coil is then set such that the projectile position is anywhere from 0 mm to 18 mm with a linear step of 1.6 mm. The triggering position inside each drive coil is measured w.r.t. the rear end of the corresponding drive coil. The analysis presented in this paper will help better understand the operation of a multistage induction coilgun.
|12:00pm - 1:30pm||Diversity & Inclusion Lunch|
Location: Ballroom AB
|1:30pm - 3:00pm||Posters: Solid State, Power Electronics, High Voltage, Biomedical|
Location: Ballroom D / Henley Concourse
Session Chair: Xiu Yao, University at Buffalo
Poster 2: 1
Design and Implementation of the SML Modulators for the ESS Linac
1Lund University, Sweden; 2European Spallation Source ERIC
The European Spallation Source (Lund, Sweden) is an under construction multi-disciplinary research facility to be based around a Linear Particle Accelerator which is to provide 2.86 ms long proton pulses at 2 GeV at a pulse repetition rate of 14 Hz, representing an average beam power of 5 MW. To accommodate the requirements of the proton linac, a large number of klystrons driven by solid state modulators rated for pulse amplitude 115 kV/100 A, pulse length 3.5 ms, pulse repetition rate 14 Hz, and pulse rise time on the order of 120 µs are required. These klystron modulators implement the novel Stacked Multi-Level (SML) modulator topology.
In the SML topology, the input stage capacitor chargers are based on an AC/DC Active Front End (AFE) rectifier and DC/DC buck converter chain. The AFE generates a stable dc-link voltage while shaping the line current to be sinusoidal and in phase with the line voltage, effectively eliminating line current harmonics and reducing reactive power to a minimum. The DC/DC converter connects the dc-link to the main capacitor bank energy storage via an inductive link, controlling the charging current to exhibit inverse waveform with respect to the capacitor bank voltage such that the required energy is replenished just in time for the following pulse, yielding constant power charging and thus flicker mitigation despite the high power pulsed load. Pulse generation is achieved in a pulse modulation/demodulation scheme as follows. First, a DC/AC inverter (H-bridge) generates an AC square voltage waveform fed to a high voltage high frequency (HVHF) transformer providing voltage amplification. Then, the amplified voltage waveform is rectified in an AC/DC high voltage diode rectifier stage and subsequently filtered, re-creating the fundamental shape of the output pulse. The topology is modular, with the implemented modulators for the ESS Linac utilizing three parallel connected input capacitor chargers and six series connected high voltage modules, increasing system power density and facilitating maintenance.
This paper presents key points, the working principle as well as the design and control of these modulators while highlighting the details of their practical implementation. Issues related to optimization, high voltage design (e.g. field control and details on the use of 3D finite element electromagnetic analysis in design), modeling and mitigation of circulating currents due to parasitic capacitive elements, and thermal management/lifetime considerations of IGBTs in high power pulsed applications are treated. Experimental results and efficiency measurements obtained in full power testing of the implemented modulators are presented.
Poster 2: 2
Triggered Spark Gap Evaluation and Optimization for Low Jitter, High Reliability Applications
Lawrence Livermore National Laboratory, United States of America
This paper discusses the evaluation and performance of three-electrode triggered spark gap switches for use in a low turn-on jitter, low pre-fire probability tolerant application. Turn-on jitter, turn-on delay time, pre-fire/no-fire occurrence, and shot life were recorded using an automated testbed for High Energy Devices TA5.0 and Excelitas GP489 spark gaps. The spark gaps were tested at 3.5kV with 1.2kA of peak current and 10mC of charge transferred per shot. The testbed apparatus and data results are shown for trigger modes A, B, and C using manufacturer-recommended triggering circuitry. Spark gap failure modes and optimum trigger modes are identified. A method for minimizing turn-on jitter using a nanosecond rise time trigger circuit with optimized trigger pulse energy for the TA5.0 spark gap is shown which achieves turn-on jitter less than 2ns.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Poster 2: 3
Pulsed Power Supply for Magnet Quench Training
Fermi National Accelerator Laboratory
Superconducting magnets typically go through a series of spontaneous “training” quenches as their current is increased towards its design value. A device has been designed and built to boost the magnet current at the moment a quench has been detected to possibly decrease the number of these quenches. The aim of the boost is to drive the magnet coil further along towards its maximum current with each training quench, and hence reduce the number of quenches required.
The current boost is accomplished by diverting the current in the magnet circuit from a diode in series with the load to a charged capacitor ( 400 mF charged to 1 kV) connected across the diode. The output terminal of the capacitor is connected to the cathode of the diode by closing IGBT switches. The connection initially adds 1 kV to the magnet voltage and drives its current up rapidly. The voltage on the capacitor bank discharges to zero as its stored energy transfers into an increase in magnet current above the quench level. The energy transfer time is some tens of milliseconds, after which the magnet protection is initiated.
The circuit has been built and is being commissioned. The design, protection systems and tradeoffs will be discussed.
Poster 2: 4
A 300 kA Pulsed Power Supply for LBNF
1Fermi National Accelerator Laboratory; 2SLAC National Laboratory
The Long Baseline Neutrino Facility (LBNF) will produce the world’s most intense neutrino beam. Three series connected magnetic horns will require 5 kV, 300 kA, 800 µs pulses at a rate of 0.7Hz to focus the beam. Fermilab has designed and built pulsed high current supplies for horns in the past. Pulsed currents of 205 kA for Neutrinos at Main Injector (NuMI / NOvA), focusing a 120 GeV beam, and 170 kA for Booster Neutrino Bean (BNB / MiniBooNE) for focusing an 8 GeV beam have been operational for about 18 years. It is required that the LBNF horn power supply last the lifetime of the project, 30 years.
A resonant, half sine wave pulser was used for NuMI and BNB and has many practical advantages. The system has impedance limited fault currents by design, albeit large ones. The pulse length of 800 µs is needed to meet the required flatness of the focussing field. The resonant behavior means that thyristor switches are well suited for this application. The design will continue the use of many pulser circuits in parallel to provide the high current. Only 30% of the initial energy stored in the capacitors is lost, based on load estimates, so an energy recovery system that is also resonant will be used to reduce charging supply size. Many fault modes of the system have also been calculated. Several circuit changes were incorporated so that a single fault can be tolerated. The supply must also be reversable to enable both neutrinos and anti-neutrinos to be produced. The reversal requirement required a significant amount of mechanical design features as the first horn must always be at the lowest potential. This requires the output polarity to change and reversal of all the semiconductors. Further design considerations will be discussed, and prototyping has begun.
Poster 2: 5
High-Speed Imaging of Exploding Detonators
1Los Alamos National Laboratory, United States of America; 2Texas Tech University; 3Scientific Applications & Research Associates
An experiment for imaging detonators used in explosively driven pulsed power applications with high-speed, short exposure time cameras will be described in the work to follow. Three, commercially available, high intensity, pulsed xenon light sources (> 107 candela intensity) yielded unsatisfactory image quality with a minimum exposure rate (~320 k frames per second). Above 320 k frames per second, the combined output intensity of the light sources were too dim. Due to this, a lamp system was designed that would be capable of delivering higher light intensity to the target.
Two types of lamp arrays were designed and tested. The first was a large lamp array comprised of a couple high energy flash lamps, while the second was a small lamp array comprised of many low-energy flash lamps. The large lamp array was intended for multiple shot use, and was placed behind a protective sheet of polycarbonate to separate the bulbs from the detonator. The second small lamp array with low-cost flash lamps was intended for one time use and will be placed closer to the detonator. Multiple five stage, Rayleigh Pulse Forming Networks (PFNs) were developed to find the optimal energy for the flash lamp array. Each PFN was modeled using LTSpice circuit simulator to verify proper operation, and help with optimization. Experimental measurements were taken of the PFN’s voltage and current outputs and compared to simulated values. A photodiode was used to measure relative light intensity from the different lamp arrays.
Poster 2: 6
The next step progress for a skin effect opening switch construction ( the resistive version)
free, Russian Federation
The next step progress for a skin effect opening switch construction
( the resistive version)
Moscow, Troitsk, Russian Federation, 108841.
A skin effect opening switch based on a transformer inductive energy storage (LSEOS) was offered for consideration in [1-2] and its resistive version (RSEOS) was offered in  too. The latter possesses some properties of contactors. For example, it is able to carry kiloamperes current during one second and more with minimal losses. Combined with auxiliary elements (an opening switch, a capacity bank and others) the version RSEOS is converted to an opening switch configuration, where the version RSEOS gets dynamic properties. Embedded in pulsed power generator based on inductive storage as a component, the received configuration of RSEOS requires the generator adaptation to a load. There are many different loads: -inductive, resistive, nonlinear and others kind of one. Each of them claims itself approach to solve a problem of adaptation. Realized by a developing technology, an engineered impulse device is able to generate nanosecond high-voltage pulses. It lets to solve some pulsed power tasks effectively, for example, a pulse train generation of a terawatt level using direct current. Besides energy storage and its output to a load is concurrent activities .
There are many parameters of pulsed power generator exerting influence on a pulse form in a load. Some of them are the parameters of a high-ohm layer RSEOS, such as depth, d, and conductivity, ρ. A time current diffusion in a solid-state conductor is tdif = (d2μ0/4ρ), where μ0=4π∙10-7 H/m. It is obviously that changing conductivity ρ, the time characteristics of the pulse changes, especially its the trailing edge too. Influence of heating and melting of the high-ohm layer on a pulse form during pulse generation for different amount of current density is discussed in this presentation. All computations were performed for a resistive load. The offered construction of RSEOS is reusable. It lets to expand a field of application.
1. O.G. Egorov, “Pulsed power generator based on inductive storage and skin-effect opening switch (energy correlation and technical application)“ Proc. PPC, Brighton, UK, June, 2017, p.280
2. O.G. Egorov, Patent No.2680343 “The method of energy output form transformer inductive storage to a load.” Patent of Russian Federation, 02.11.2017.
3. O.G. Egorov “Combination of skin-effect opening switch and auxiliary opening switches for inductive storages application (narrowband and wideband devices)” Proc. PPC, Denver, USA, December, 2021. (to be published).
Poster 2: 7
SLAC LINAC Sub-booster Modulator Upgrade with Solid State Switch
SLAC National Accelerator Lab, United States of America
The LINAC sub-booster modulator was designed in the 1960s and has serviced SLAC LINAC about 60 years without primary switching upgrade. The primary switch for the high power pulse are two parallel vacuum tetrodes. Recently the vacuum switch price has surged, probably because more and more customers have shifted to the solid-state switch from the vacuum switch. Anticipating the vacuum switch will finally become obsolete, some solid-state switches have been tested and their performance evaluated in SLAC LINAC sub-booster modulators. In this paper, the design and performance will be reported.
Poster 2: 8
X-Band TWT Transmitter
Diversified Technologies, Inc., United States of America
In 2021 Diversified Technologies, Inc. (DTI) developed and installed a high power X-band transmitter into a new radar. The transmitter’s design is closely based on several high power traveling-wave tube (TWT) transmitters previously delivered by DTI. This X-band transmitter employs the Communications and Power Industries’ (CPI) TWT, model VTX-5681B3, to deliver a peak power of 130 kW at 35% duty. DTI built the modulator and other electronics subsystems, purchasing and integrating the RF systems for the transmitter, as well as providing cooling on a dish antenna. This on-mount arrangement gives the most direct waveguide run from the TWT to the antenna feed network, resulting in the lowest microwave losses and maximum transmitted power. The remainder of the transmitter electronics are mounted on the ground near the antenna pedestal in a DTI-supplied shelter. A single DTI-supplied cooling skid provides system cooling for both transmitters delivered.
DTI’s X-band transmitter consists of state-of-the-art, solid state, high-voltage subsystems. The speed, precision, and reliability of solid state devices offer a level of performance unattainable in conventional transmitter designs. The only vacuum electron device (VED) in the transmitter is the CPI VTX-5681 very high power coupled-cavity TWT.
Poster 2: 9
High Stability Klystron Modulator for Commercial Accelerator Application
Diversified Technologies, Inc., United States of America
Diversified Technologies, Inc. (DTI) designed and developed a high stability modulator system for a commercial linear accelerator application. The DTI modulator delivers significant advantages in klystron performance through highly reliable functionality as well as flicker- and droop-free operation from 50-500 μs up to 400 Hz (duty limited). The main assemblies on the DTI system consist of a controls rack, high voltage power supply (HVPS), modulator, and cooling manifolds for the modulator, high voltage power supply and klystron tube. Two HVPS (upgradeable to four) provide stable and accurate DC voltage which is used to drive a CPI VKP-8352C UHF-band pulsed klystron for the linear accelerator. A solid state series switch, based on DTI’s patented design, provides both pulse control and arc protection to the klystron. Operating with four HVPS, the DTI modulator is able to operate at a maximum average power of ~750 kW at 105 kV, 47 A nominal. At the end of the initial contract, DTI provided two systems and a total of four HVPS (two of which are used with each system).
Poster 2: 10
Aluminum electrolytic capacitor vulnerability evaluation in DC power supplies at the Spallation Neutron Source
Oak Ridge National Laboratory, United States of America
The service life of electrolytic capacitors is a concern for long-term reliable operation of power supplies. The Power Conversion Group at the Spallation Neutron Source (SNS) facility of Oak Ridge National Laboratory is responsible for more than 500 power supplies with over 1000 electrolytic capacitors installed in these power supplies. Most of the electrolytic capacitors are in operation since 2007 and are either well over or close to the manufacturer provided lifetime. This paper addresses this vulnerability to ensure continued reliable operation of the SNS. The power supply circuit will be simulated in a MATLAB/Simulink environment to quantify the capacitor ripple current and operating voltage. Combined with manufacturer data, this information will be used to estimate capacitor lifetime. Utilizing the simulation results and lifetime projections of the capacitors, capacitor replacements for the power supplies will be prioritized. To assess end-of-life, the ambient temperature and ripple current of the capacitor is used. Based on the manufacturer’s data and scientific literature review, capacitor end-of-life will be established. The results of the simulations and analysis will be presented. Data on the highest priority supplies will also be presented, and statistics on the capacitor performance, reliability and remaining lifetime will be shown.
Poster 2: 11
Duty Cycle Adjustable High-Voltage AC Power Supply with High Repetition Rate
1INSTITUTE OF ELECTRICAL ENGINEERING,CHINESE ACADEMY OF SCIENCES, China, People's Republic of; 2University of Chinese Academy of Sciences
Low-temperature plasma has a wide range of applications and unique superiority in environmental pollution improvement, biomedicine, materials modification and energy conversion due to its electrical and physical properties. For industrial applications, adopting AC power supply for generating plasma is also a most common method due to high stability of system. However, the application of ac mode also brings forward the demand of more efficient operation modes which include alterable duty cycle , adjustable amplitude of output voltage and repetition rate. To decreasing the dimension of whole systems, we sacrificed some adjustable range of variable parameters. The main circuit of presented power supply utilize push-pull circuit since no need for considering potential problems of gate drive for switches, and the auxiliary circuit consists of dual channel output gate driving circuit with adjustable duty cycle and step-down circuit. As a result, the AC power supply can generate output voltage~6 kV, peak repetition rate ~20kHz, which is expected to be applied in DBD load in the future for demonstration of generating plasma.
Poster 2: 12
A high-power pulse resistor with nonlinear low inductance
1Hefei University of Technology, China, People's Republic of; 2Hefei Hangtai Electrophysics Co. Ltd
High-power pulse resistor used in surge current Marx generator shall adjust the current waveform with desired inductance. However, the demand of low inductance is always conflicted to the size of resistor for its low resistance with surge current lager than 10kA. To break through the limited application, here, a high-power pulse resistor of multi-conductor coaxial structure, made out of ferromagnetic material (OCr25Al5), that works in magnetic saturation is designed. Our test results showed that the resistor is about 400mΩ, the inductance decreases nonlinearly with current amplitude and could be much small as 1.7μH in 30kA. This inductance allows the resistor meets lots of surge current generator requirements, especially in lightning current waveform generation. More importantly, the resistor size compared to general pulse resistors decreased vastly. Our study illustrates that that resistor design could be well used in supporting generation of high-amplitude pulse current waveform.
Poster 2: 13
A low cost, fast rise time, 120 kV multiple use Pulsed Power trigger generator
Loughborough University, United Kingdom
A pulsed power trigger generator is introduced, having a simple design based on ceramic capacitor stacks having a total capacitance of 5.3 nF, mounted inside an oil-filled cylindrical-coaxial transmission line. After being charged to 120 kV, the unit is discharged by a self-breakdown spark-gap switch, generating an output voltage impulse with a rise time of only a few ns. Experimental data is provided for the pulsed generator operated with various loads.
Poster 2: 14
An Experimental Apparatus for Novec 4710 for Pulsed Power Applications
1Texas Tech University, United States of America; 2Lawrence Livermore National Laboratory
Sulphur hexafluoride (SF6) is a prevalent insulating gas in high voltage environments. However, the high global warming potential of SF6 has motivated a search for an alternative, more environmentally friendly insulating gas. Novec 4710 (C4F7N) is a primary candidate due to potentially having nearly twice the voltage hold-off of SF6, significantly lower atmospheric lifetime, and a greatly reduced greenhouse effect.
While prior work has focused chiefly on DC and AC (power utility) frequencies, an experimental apparatus was developed to assess the pulsed power performance characteristics of Novec 4710 in mixtures with CO2 and N2 at pressures of up to three atmospheres. The pressure chamber has interchangeable anode and cathode connections to facilitate the testing of multiple breakdown geometries such as plane-to-plane, rod-to-plane, et cetera. The electrode design permits the study of various electric field gradients on the hold-off voltage of Novec 4710. Within the chamber, the electrodes are integrated as center conductors in a 50 Ohm coaxial transmission line geometry. Thus, the system maintains 50 Ohm impedance throughout the geometry, thereby minimizing reflections and allowing for voltage and current diagnostics with fast, nanosecond resolution.
Poster 2: 15
Development of a Magnetron based S-band High Power Microwave Test Bed
Texas Tech University Center for Pulsed Power and Power Electronics
This poster reviews a magnetron based high power microwave (HPM) system and subcomponents for producing ~2.5 MW HPM pulses with ~ 3.6 µs pulse duration. This system utilizes a 5-stage, 25 Ohm, Guillemin quasi-type-E pulse forming network (PFN), initially charged to 24 kV. The PFN delivers 12 kV to a matched load, which consists of a 1:4 transformer to drive a high power magnetron (EEV M5193) with up to 48 kV and 110 A (~400 Ohm effective impedance). The electrical performance characteristics of the PFN with resistive load terminations are reported and compared with circuit simulation. Preliminary HPM performance characteristics are reported.
Poster 2: 16
Design Challenges in High Current Pulsed Striplines
Fermilab, United States of America
The Long Baseline Neutrino Facility (LBNF) will produce the world’s most intense neutrino beam. Three series connected magnetic horns will require 5kV, 300kA, 800µs pulses at a rate of 0.7Hz to focus the beam. Connecting a single power supply to these focusing horns will require a low impedance connection measuring over 60 meters in length. In order to meet the challenging requirements of connecting the horns to the power supply, this connection is engineered as a nine-conductor, high-current pulsed stripline. It must pass through a harsh radiation environment, be passively cooled, and have an operational lifetime of at least 30 years. This paper discusses mechanical and electrical considerations such as high-voltage holdoff, clamped joint performance, and Lorentz force mitigations in order to meet the specified requirements. The results of tests and experiments on several prototypes of key design features will be presented and discussed.
Poster 2: 17
The Recent Improvements of the SNS Extraction Kicker Power Supplies
Oak Ridge National Laboratory, United States of America
A total of 14 extraction kickers, with one as the hot spare, are in service to extract protons out of the storage ring at SNS. The jitter issue and the short lifetime of the switches were resolved after the thyratrons were replaced with solid state switches in 2018. This paper discusses the recent improvements. Two thyristor switches suffered overheating damage in separate incidents. One was due to the oil pump failure and the other was the result of a disconnected oil hose. An ultrasonic flow meter and fiber optic temperature monitors have been installed for each extraction kicker power supply. The flow meter continuously monitors the entire tank oil flow. The temperature monitors detect the thyristor switch real-time temperatures in three locations. Fault thresholds are selected so that the thyristor switches are protected from overheating damage. Alarms are configured to alert staff to take actions before faults occurs. In addition, the cause of an intermittent mis-fire issue was identified, and the solution was implemented. Lastly, a future oscilloscope upgrade is discussed.
Poster 2: 18
Los Alamos National Laboratory Fast Kicker Upgrade 2022
Los Alamos National Laboratory, United States of America
The Los Alamos Neutron Science Center’s proton storage ring (PSR) extraction kicker systems consist of two thyratron switched blumlein modulators. The operating parameters of the PSR have changed over the years and the flattop voltage of the modulator outputs has become a limiting factor in the length of the beam pulse able to be extracted from the ring. The extraction voltage pulse travels upstream relative to the beam and thus needs to be longer than the beam pulse. A reanalysis of the voltage waveforms and the beam propagation times revealed that a longer pulse could reduce beam spill levels that have been seen during past run cycles. Reduced spill will allow operation at higher beam currents and thus increase the amount of beam current available for experimenters. We have upgraded the blumlein cables in both extraction kicker modulators with longer cables. We present test results of the modulator outputs and correlate their improvement with reduced beam losses at the PSR exit septum and improved beam delivery.
Poster 2: 19
Fast Measurements with Modified HVD Series of High Voltage Dividers
Spellman High Voltage Electronics Corp., United States of America
HVD Series of precision high voltage dividers manufactured by Spellman  are specified for DC measurements only. As such, they possess very high input impedance (1 GOhm and higher) and are corona-free.
We modified 100‑kV and 200‑kV models for time-domain measurements, extending the range of HVD100 to 140 kV. These models are dubbed HVD100C, HVd140C, and HVD200C (C stands for “compensated”). The last two models have also modified corona suppression electrodes, and E-field analysis is described showing that the field is below corona inception. Typical usable risetime is 2 us for 100‑kV and 140‑kV models, and 10 us for the 200‑kV kV model. Settling time to 0.2 % is less than 2 ms.
HVDs are calibrated for fast response both at low and high voltage by step response method; calibration results are provided. The modified, compensated, versions retain the same DC accuracy as their original DC counterparts.
The modified HVDs are useful for laboratory and manufacturing practices when HV time domain measurements are necessary in combination with high DC accuracy and high input impedance.
 Resistive Voltage Dividers, https://www.spellmanhv.com/en/high-voltage-power-supplies/HVD
Poster 2: 20
A Multi-Hundred kW HV Power Supply Platform with Low Stored Energy for Industrial Applications
Spellman High Voltage Electronics Corp., United States of America
A modular concept and industrialized demonstration of a 200kW, 45kV power supply possessing high dynamic characteristics is described. The system is comprised of eight 25kW, 45kV chassis connected in parallel and a control unit. Owing to the phase shift within and between the modules, high conversion frequency, and straight rectification schemes, the output capacitance is extremely low, which facilitates fast dynamic response, e.g., fast recovery after load sparking; stored energy is <10J, and ripple is <1% at full load.
The system is housed in three cabinets. Each chassis is packaged in a 19” 6U rack and weighs 45kg. Solid insulation and air cooling were adopted. Mechanical and electrical designs were assisted by circuit and FEA analyses. Particular attention, in view of high-power density, was paid to heat transfer, which was analyzed from the component level up to CFD modeling at the chassis and cabinet levels.
A variable parameter PID regulator achieves 300us rise time for a full range of loads without over/undershoots.
Poster 2: 21
Electric Field Driven Ionization Waves in Nanosecond-pulse Discharge
1Institute of Electrical Engineering, Chinese Academy of Sciences, China, People's Republic of; 2University of Chinese Academy of Sciences
Electric field is an extremely important microscopic parameter in the subject of high voltage (HV) and gas discharge. In this paper, electric field induced second harmonic (E-FISH), as a non-intrusive diagnostic method for electric field, is developed with good temporal and spatial evolution. This method is adopted to measure the spatial-temporal distribution of electric field in nanosecond pulsed discharges, including surface dielectric barrier discharge (SDBD)  and atmospheric pressure plasma jet (APPJ) , which verifies its reliability and feasibility. It is found that ionization waves (IWs) exist universally in nanosecond-pulse discharges with different geometries, which are driven by the intensified electric field at the wave front region. The weak electric field in the plasma channel is also very important for sustaining the IW propagation. Both space charges in surface and volume charges on dielectric will contribute to the measured electric field, the former of which generate a retarding electric field when IW propagates driven by unipolar HV pulses. To summery, the E-FISH diagnostic is a promising method to measure the space electric field and to retrace the behavior of space charges in a wider field of applications.
Poster 2: 22
Calculations of pulsed magnetic Field Interactions with Neurons using Sim4Life
1Purdue University, United States of America; 2Veritas Alchemy LLC; 3Luna Innovations
As medical applications of electromagnetic radiation transition from in vitro tests to the clinic, understanding multiscale behavior from the molecular to organism level becomes critical. This necessitates accurately modeling the interaction of electric fields at not only the cellular level, but at the tissue level. While many studies have investigated mechanisms at the cellular level, modeling in vivo effects requires determining the interaction of an applied electric field with the tissue before predicting cellular behavior . However, it can be difficult to ascertain how the different components in these systems will interact as they are vastly complicated compared to the single cell models explored already. This is even the case when considering something as apparently simple as dielectric properties, which will vary with tissue type and location throughout the body. Sim4Life (https://zmt.swiss/sim4life) is a multiphysics software that was specifically developed to perform these calculations from the electromagnetic source to the tissue level by considering the physical and dielectric properties of phantoms for an organism of interest. Furthermore, Sim4Life contains the functionality of integrating NEURON, which is an open source software that specifically assess the effect of an electric stimulus on neurons . This integrated software provides the user the flexibility to characterize changes in neuron behavior, such as action potentials, from an electromagnetic stimulus.
As a first step in this process, we are modeling the interaction of a pulsed magnetic field (PMF) applied to a rat model using Sim4Life. We will specifically consider the effects of pulse duration, rise- and fall-times, and repetition rates of the current source used to generate the PMF under the idea that the magnetic field will induce an electric field that will change the transmembrane potential of the exposed cells . Whether permeabilization is induced, we will be able to use the integrated Sim4Life and NEURON software to explore changes in the action potential for various PMF exposures, delivery mechanisms, and positions along the rat. Modifications of this model to assess ex vivo proof of principle experiments to benchmark the model prior to using it to guide in vivo tests on rats will be discussed.
This research was funded by the Defense Health Agency under contract #W81XWH-20-C-0094.
 D. Sel, et al., “Sequential finite element model of tissue electropermeabilization,” IEEE
Trans. Biomed. Eng., vol. 52, pp 816-827, 2005.
 M. L. Hines and N. T. Carnevale, “The NEURON simulation environment,” Neural
Comput., vol. 9, pp. 1179-1209, 1997.
 Q. Hu, R. P. Joshi, and D. Miklavčič, “Calculations of cell transmembrane voltage induced by
time-varying magnetic fields,” IEEE Trans. Plasma Sci., vol. 48, pp. 1088-1095, 2020.
Poster 2: 23
Modeling Plasma Membrane Pore Dynamics During Exposure to Electric Pulses Delivered by a Mismatched Blumlein Transmission Line
1Purdue University, United States of America; 2Texas Tech University, United States of America
Electroporation occurs in cells when an applied electric pulse (EP) induces a transmembrane potential above a threshold to cause an increase in the plasma membrane conductivity. Many experiments, mathematical models based on the Smoluchowski equation (SME), and molecular dynamics simulations have examined the phenomena responsible for this behavior for standard rectangular or trapezoidal waveforms. In practical experiments, the applied waveforms differ from these idealized shapes, particularly when applying multiple EPs that permeabilize the cells and cause ion transport between the cytoplasm and extracellular fluid that causes a mismatch between the impedance of the cell suspension and the pulse generator. For the Blumlein generators often used for nanosecond EP delivery, these mismatches can create fluctuations in the pulse waveforms, including periodic waves after the main rectangular EP . While important for applications involving multiple EP delivery, pore dynamics for a sinusoidal electric field after a rectangular EP have not been commonly studied. One study used the asymptotic SME to show that applying an AC field immediately after a square pulse could extend pore lifetime if it induced a sufficient amplitude of the transmembrane potential . This then raises the question about the implications of mismatch-induced sinusoidal electric field following the applied rectangular pulse on membrane pore dynamics, particularly depending on the frequency and intensity of this sinusoidal component. This presentation examines this behavior by applying an asymptotic Smoluchowski equation (SME)  to model membrane pore dynamics for a cell exposed to EP waveforms characteristic of these mismatches. We will examine the effects of the frequency and amplitude of the secondary sinusoidal electric fields on membrane pore dynamics for main EPs of various rise- and fall-times, pulse durations, and electric field. We will also compare the results from this model to a simplified electroporation model based on transmembrane potential and assess potential intracellular effects that may arise due to these more realistic pulse waveforms.
 J.F. Kolb, S. Kono, and K. H. Schoenbach, “Nanosecond pulsed electric field generators for the study of subcellular effects,” Bioelectromagnetics, vol. 27, pp. 172-187, 2006.
 A. L. Garner and V. B. Neculaes, “Extending membrane pore lifetime with AC fields: A modeling study,” J. Appl. Phys., vol. 112, 2012, Art. no. 014701.
 S. Talele, P. Gaynor, M. J. Cree, and J. van Ekeran, “Modelling single cell electroporation with bipolar pulse parameters and dynamic pore radii,” J. Electrostatics, vol. 68, pp. 261-274, 2010.
This research was funded by the Office of Naval Research under grant #N00014-21-1-2055 and the Defense Health Agency under contract #W81XWH-20-C-0094.
|3:00pm - 3:30pm||Coffee Break|
Location: Ballroom AB
|3:30pm - 5:30pm||Dielectrics II|
Location: Ballroom C
Session Chair: Kevin Burke, University at Buffalo
3:30pm - 3:50pm
Dielectrics II: 1
Electrostatic Surface Charge Decay of Floating Dielectrics
1Texas Tech University, United States of America; 2Pantex, Amarillo Tx. United States of America
Electrostatic surface charge accumulation on dielectric materials, followed by surface charge decay, is investigated. This work focuses on charging floating dielectric surfaces to the limit of electric breakdown in atmospheric air in humid and dry conditions, succeeded by the slow charge decay on the timescale of minutes to hours. The mechanisms leading to reducing the surface charge density include surface charge cancellation from ions attracted from the surrounding gas medium as well as charge migration along the dielectric. A 100 mm diameter sphere of varying materials (Teflon, Acrylic, and metal as a reference) was triboelectrically charged to tens of kilovolts and allowed to decay uninterrupted in relative humidities of 40% and 12%.
While the metal sphere charge decay was largely unaffected by the humidity, the dielectrics exhibited a much faster surface charge density decay in humid conditions, particularly when the surface charge initially covered only a fraction ~ 10 to 25% of the sphere. That is, the humid conditions cause moisture layers to form on the dielectric’s surface, impacting the surface conductivity of the material and allowing charge to redistribute along the surface. For instance, one finds an exponential dependence of the conductivity on the number of adsorbed water layers for Teflon and quartz reported in the literature.
For acrylic, in humid air, an initial drop in voltage upwards of 30% of the initial charging voltage was observed over 5 seconds. This rapid voltage drop is attributed to charge redistribution occurring on a much faster time scale than the air-ion to surface charge recombination. Further experimentation on decay behavior from uniformly charged dielectric spheres and partially charged spheres was conducted. This work provides details on the nonlinear surface conductivity, which is found to be electric field dependent.
3:50pm - 4:10pm
Dielectrics II: 2
Characterization and Modeling of electrostatic Discharges on floating dielectric Materials
1P3E Center, Texas Tech University; 2Mission Engineering Development Group, CNS Pantex; 3Facility Engineering Electromagnetics Group, CNS Pantex
Electrostatic Discharge (ESD) waveforms are measured for polymeric materials – PTFE, PMMA, PA6 – with high-speed (sub-nanosecond) current viewing resistors (CVR). These waveforms are used to create lumped element models which capture the behavior in addition to a comparison to a drift-diffusion numerical simulation. Cylindrical dielectric samples without a well-defined ground (i.e. samples are ‘floating’) are of particular interest in this study. The ~100 mm diameter samples are charged primarily via triboelectric means to high voltage – greater than 20 kV. The surface charge distribution is mapped before and after a discharge to determine energy lost to establishing the spark, conduction to ground, and radiation – captured with a B-Dot probe. A three-axis – R, Z, and rotational Phi – movement system was created to perform the mapping of charges and control the approach speed of the discharging electrode. Discharge electrodes consisting of spheres of 5-20 mm diameter and pointed electrodes with tip radii ranging from 0.1 to 1 mm are used with approach speed ranging from 10 to 150 mm/s. The radiated field from the B-dot probe exhibits a sharp peak at ~1.5 GHz, temporally coinciding with peak current. Discharge waveforms are similar in shape between materials and charging polarities; however, peak current and length change. For instance, PTFE charged negatively creates a spark 150-200 ns in length, whereas positively charged PMMA creates a spark 100-150 ns in duration. Peak currents, on average, are similar between materials and polarity, ~0.2 A, and peak dI/dt range from 0.3 to 0.57 A/ns for PTFE and PMMA, respectively.
Through pre- and post-mapping of the surface charge, the discharged area of the charged dielectric is captured. The discharged areas range from 4 to 8 cm2, with the charge maps revealing extended surface tracking mainly parallel to the symmetry axis of the cylinder.
With the spark length mainly dependent upon the approach speed for the same voltage, namely that faster approach speeds result in shorter sparks, one may expect lower speeds to exhibit lower peak current – that is, a longer spark would be suspect of losing more energy in establishing the spark. However, in experimental studies, this doesn’t always occur. While a Rompe & Weizel spark model with an RC object model captures the basic behavior of the discharges, the drift-diffusion model reveals the fundamental physics at play. The numerical simulation captures the electron and ion motion/generation/loss and includes modeling the emission process of charges from the dielectric surface.
4:10pm - 4:30pm
Dielectrics II: 3
A Finite Element Analysis Model for Internal Partial Discharges under DC Voltages
1Virginia Tech, United States of America; 2University of New Mexico, United States of America; 3Avalanche Energy Designs, United States of America; 4University of Manitoba, Canada
While the PD topic is booming for ac systems, it is immature for dc systems. Also, although much work has been done and significant progress has been made on PD measurement and detection techniques, this is not the case for PD modeling. To address these technical gaps, a finite element analysis (FEA) model for internal PD under dc is, for the first time, developed to help understand the mechanisms behind PD under dc voltages. The model is validated through experimental studies where testing samples, one with a void and another without any void, are built using 3D printing. The sample with a void has a void inside, which will cause internal PD. There is a good agreement between the measured and simulated magnitude of charges and the frequency of PD signals under dc voltages.
4:30pm - 4:50pm
Dielectrics II: 4
Federal University of Campina Grande, Brazil
The transmission of electrical energy in the world is predominantly provided by High Voltage Alternating Current (HVAC) lines. However, High Voltage Direct Current (HVDC) lines have gained space in power transmission over long distances. As the transmission lines, both in HVDC and HVAC, are susceptible to efforts from the environment and from the action of electromagnetic fields in transmission energy process. Such efforts wear out the materials that make up the system, especially the insulators, which can lead to failures and interruptions in the electricity supply. One of the main causes of interruptions, whether scheduled or unscheduled, is associated with the performance of electrical system insulation. In the case of electrical transmission and distribution systems, the insulation between the conductors and the towers is carried out by atmospheric air and by components called electrical insulators. Among electrical insulators, polymeric insulators have a prominent role due to their comparative advantages to ceramic insulators. To mitigate insulation failures that are related to polymeric insulators, it is recommended the use of predictive techniques to identify damages that could compromise the system. A prominent technique in the electrical system is infrared thermography. It suggests that the presence of defects in the polymeric insulators causes an increase in the local leakage current, which generates abnormal heating of the component. In AC, the technique is used by power utilities due to its electrical efficiency and usability in other equipment. In DC, operational experience using thermography to identify defective individuals has not been documented. This work presents a comparative analysis of the techniques for the application of infrared thermography in polymeric insulators in research on alternate (AC) and direct (DC) voltages. Therefore, electrical tests in AC and DC were carried out on polymeric insulators with different operating states. It was observed that polymeric insulators with degradations around the core, associated or not with fiberglass exposure, cause localized heating in the AC test. The generated heat identifies faulty regions in the insulators and allows effective monitoring of the evolution of damage to the polymeric coating. On the other hand, the results obtained from the insulators in DC did not identify a significant increase in temperature in any region of the insulator. The low value of the leakage current was the cause indicated for the thermal profiles obtained in the DC test. The results indicate that, in general, they use as monitoring techniques what is not possible to identify an isolated condition directly, except in cases where the defect is quite severe.
4:50pm - 5:10pm
Dielectrics II: 5
Effect of Titania Nanofiller on Electrical Tree of Silicone Gel
1Nagoya University, Japan; 2Toyohashi University of Technology
In recent years, to reduce the size and increase the power density of power modules, the inside of the module is exposed to high electrical fields. The high electric fields may cause electrical tree in the silicone gel used as an encapsulant inside the module. As a result, the electrical insulation strength and the insulation life of the silicone gel deteriorate. Therefore, it is very important to suppress the generation and development of electrical tree to extend the service life of the material. The addition of nanofillers to silicone gels has been found to be effective to suppress the generation and propagation of electrical tree. In a previous study, it was confirmed that the addition of titania had a significant effect on the suppression of electrical tree. However, the data showed some variability. Therefore, to increase the reliability of the verification of the suppression effect, we refined the evaluation conditions for the electrical tree. The breakdown experiments were conducted by setting several patterns of voltage increase speed, and it was confirmed that the higher the voltage speed increase, the higher the breakdown voltage. In addition, titania was added to the silicone gel to investigate the difference in the effect of improving dielectric strength depending on the amount of titania added. The samples were subjected to ultrasonic treatment to disperse the titania particles. As a result of the experiment, the sample with 0.1 vol% titania showed the highest breakdown voltage when the voltage was applied at 10 kVrms/sec. Further, we observed the progress of the electrical tree. The samples were centrifuged to remove micro-sized agglomerates. The filling rate after centrifugation was as small as 0.05 vol% or less, so it could not be measured, but since the sample itself was cloudy, it is considered that agglomerates or nanoparticles of a size that cannot be observed with an optical microscope remain. The AC voltage of 50 Hz was applied to the needle electrode at 0.14 kVrms/5 sec, 8.5 kVrms was continuously applied, and the progress of the electrical tree was observed using an optical microscope. As a result, the outline of the electrical tree observed in the nanocomposite gel was not significantly different from that of the unfilled silicone gel. We obtained, in addition, the electrical tree of neat gel stretched to 2 mm within 500 seconds. On the other hand, the electrical tree of NC gel stretched at the same speed as neat gel to 0.5 mm, and grew more slower than neat gel from 1 mm or more. Some trees did not extend to 2 mm. From these results, it is considered that the nanoparticles in the gel suppressed the progress of the electrical tree. In the future, we will continue our research on the mechanism of electrical tree propagation in silicone gel and nanofillers that can further suppress electrical tree.
|3:30pm - 5:30pm||High Power Microwaves|
Session Chair: Jon Cameron Pouncey, Naval Surface Warfare Center Dahlgren Division
3:30pm - 4:10pm
High Power Microwaves: 1
High Power Microwave and Pulsed Power Development at the University of Michigan
University of Michigan, United States of America
The Plasma, Pulsed Power, and Microwave Laboratory (PPPML) at the University of Michigan (UM) is home to three large pulsed-power drivers: the Michigan Electron Long Beam Accelerator (MELBA), the Michigan Accelerator for Inductive Z-pinch Experiments (MAIZE), and the Bestowed LTD from Ursa Minor Experiment (BLUE). MELBA is a 7-switch Marx generator with an Abramyan circuit and is capable of generating a 10 kA electron beam at -1 MV for up to 1 µs; this accelerator is currently configured to produce -300 kV and is used for high-power microwave (HPM) research. MAIZE is a 3-m-diameter, single-cavity Linear Transformer Driver (LTD) that supplies a 1 MA, 200 ns pulse for high energy-density physics (HEDP) research. BLUE is the most recent addition to the PPPML, consisting of four 1.25 m diameter LTD cavities which were previously part of Sandia’s 21-cavity Ursa Minor facility. A single cavity of BLUE produces an estimated 150 kA at 100 kV in ~100 ns into a load matched to the driver’s 0.5 Ω impedance. The 4 cavities can be stacked for a total driver impedance of ~ 2 Ω and correspondingly increased matched-load voltage of 400 kV.
Recent HPM developments will be presented, including: a multi-frequency Harmonic Recirculating Planar Magnetron (HRPM) utilizing a dual-frequency (L-band and S-band) slow-wave structure to enable low-Q operation at the MW level; a 5 MW Recirculating Planar Crossed-Field Amplifier (RPCFA) with ~ 9 dB gain at 3 GHz; experimental demonstration of the Recirculating Planar Magnetron with Coaxial-All-Cavity Extraction (RPM-CACE); a moderate current (< 10 kA) Magnetically Insulated Line Oscillator (MILO) operating in L- and S-band; and the implementation of a GW-class MILO on the BLUE LTD.
Pulsed power developments will also be highlighted, particularly the recent improvements to spark-gap switch reliability in MAIZE. UM has tested 3 spark-gap switch designs on MAIZE, and uncovered a number of operating modes that result in inconsistent breakdown and triggering. The lessons learned from these undesirable operating conditions, and the subsequent methods to achieve reliable operation, should benefit the growing population of researchers using and designing LTDs.
Research supported by The Air Force Office of Scientific Research #FA9550-15-1-0097, FA9550-20-1-0409, and FA9550-21-1-0184, Office of Naval Research #N00014-19-1-2262, #N00014-18-1-2499, and #N00014-16-1-2353, NNSA # DE-NA0003764, DEPS Fellowship support to DP, and L3Harris Electron Devices.
4:10pm - 4:30pm
High Power Microwaves: 2
Modeling Composite Nonlinear Transmission Lines as High-power Microwave Sources
Purdue University, United States of America
Nonlinear transmission lines (NLTLs) can sharpen input pulses and induce output oscillations as high-power microwave (HPM) sources with high pulse repetition rates, frequency agility, durability, and reliability, leading to compact devices with inexpensive construction costs and reduced power consumption . In general, NLTLs use ferroelectric and/or ferromagnetic materials with field-dependent permittivity and/or permeability, respectively; implementing ferromagnetic materials produces microwave oscillations through gyromagnetic precession when biased under an external magnetic field .
In this work, we use COMSOL Multiphysics to model NLTLs containing ferroelectric and/or ferromagnetic composites and compare to experimental results. We have previously measured and simulated the linear effective electromagnetic properties of composites containing various volume loadings of barium strontium titanate (BST) and/or nickel zinc ferrite (NZF), which are nonlinear dielectric and magnetic materials, respectively . We have also measured the nonlinear permeability and nonlinear permittivity of various volume loadings of these materials. These studies demonstrate the tunability of the electromagnetic properties of the composites, which may be used to adjust the RF output from a NLTL.
To reduce computational expense, we model the composite regions in the NLTLs as homogeneous domains. To model the gyromagnetic NLTLs with ferrite composites, we solve the Landau-Lifshitz equation  and treat the gyromagnetic ratio and damping factor as fitting parameters determined by comparison to experiments. The center frequency of the output pulses primarily varies with the gyromagnetic ratio when the bias field, the incident field, saturation magnetization of the applied ferrites, and ferrite filling ratio are fixed . We compare the resulting models to experiments using NLTLs with different compositions of BST and/or NZF driven by different pulse forming lines. We then use the benchmarked model to predict performance with different materials and volume loadings to assess potential future designs. Implications for a complete HPM system design integrating an antenna and pulse forming network will be discussed.
We gratefully acknowledge funding from the Office of Naval Research (Grant No. N00014-18-1-2341).
 A. J. Fairbanks, A. M. Darr, and A. L. Garner, “A review of nonlinear transmission line system design,” IEEE Access, vol. 8, pp. 148606 – 148621, 2020.
 X. Zhu, A. J. Fairbanks, T. D. Crawford, and A. L. Garner, “Modelling effective electromagnetic properties of composites containing barium strontium titanate and/or nickel zinc ferrite inclusions from 1-4 GHz,” Compos. Sci. Technol., vol. 214, 2021, Art. No. 108978.
 I. V. Romanchenko, V. V. Rostov, A. V. Gunin, and V. Y. Konev, “High power microwave beam steering based on gyromagnetic nonlinear transmission lines,” J. Appl. Phys., vol. 117, 2015, Art. no 214907.
4:30pm - 4:50pm
High Power Microwaves: 3
System Design Considerations for a Nonlinear Transmission Line Used Simultaneously as a Pulse Forming Line and High-Power Microwave Source
Purdue University, United States of America
Nonlinear transmission lines (NLTLs) have been of increasing interest for pulse sharpening and high-power microwave (HPM) generation. Their compact form factor coupled with their inexpensive and rigid design makes them ideal for field implementation where system survivability is a concern.
NLTLs are just one subcomponent in the overall HPM systems structure. Recent efforts have examined using the NLTL simultaneously as both the pulse source and HPM generator by biasing the lines with a DC charging voltage . While this further reduces the spatial footprint of the system, such a design has inherent complications associated with extracting the signal it generates.
This work focuses on full system design considerations when using a NLTL in the PFL format. We manufactured 10-ohm composite based NLTLs that utilize a combination of barium strontium titanate and nickel zinc ferrite encapsulated in PDMS. The output of the NLTL was coupled to a pressurized spark gap switch that closed upon reaching a sufficient charging voltage. An impedance transformer was then designed to taper the impedance to a 50-ohm standard. We demonstrate that the RF output of the NLTL is a strong function of impedance with the RF signal becoming weaker with increasing impedance. This provides additional motivation for the NLTL in the PFL format since the impedance is readily flexible since it does not need to be directly matched to a Pule Forming Network. The ability to enhance RF generation with a lower impedance may permit further reduction in device size by eliminating the need for additional systems, such as a bias magnetic field. Overall implications on system development will be discussed.
1. A. J. Fairbanks, T. D. Crawford, and A. L. Garner, “Nonlinear transmission line implemented as a combined pulsed forming line and high-power microwave source,” Rev. Sci. Instrum., vol. 92, 2021, Art. no. 104702.
4:50pm - 5:10pm
High Power Microwaves: 4
RF Output Power Detection of the RADAN MG-4 Microwave Generator
Texas Tech University, United States of America
The RADAN series-based MG-4 Microwave Generator is a compact, high power microwave system developed by the Institute of Electrophysics in Ekaterinburg. The system features the RADAN high voltage generator which is a SINUS-series device featuring a Tesla transformer charger and a Blumlein pulse forming line. The MG-4 microwave head is a mm-band relativistic backward wave oscillator (BWO) that operates at 35 GHz with a 5 to 10 MW peak output power and a pulsewidth of 3 nsec. The typical method of output power measurement is done with a cryogenic detector supplied with the system which utilizes a germanium crystal that changes resistivity as microwave radiation is absorbed.
In order to confirm the rf output power level of the MG-4, and because the germanium crystal rf detector was unavailable, a commercially available rf envelope detector was employed. Analog Devices ADL6012 is a broadband envelope detector that operates from 2 GHz to 67 GHz at input powers up to +15 dBm. It also features a 500 MHz envelope bandwidth and 0.6 nsec output risetime capability.
The diagnostic setup features the ADL6012-EVALZ, an evaluation board with the ADL6012 offered by Analog Devices, shielded in a fitted brass box located in the far field (~60 cm) from the microwave output horn. The output mode of the MG-4 is nominally TM01 but a mode convertor allows for a TE11 output mode as well. The surrounding surfaces close to the detector are covered with attenuation foam to limit reflections that could possibly be detected and interfere with measurements. A 20 dBi receiving antenna and four high frequency attenuators are used to reduce the input power to the acceptable input range of the detector. Two equal length coax cables connect the differential outputs from the detector to two channels of a high-speed 1.5 GHz oscilloscope where the positive and negative envelopes of the pulse are captured separately. Based on the peak differential output voltage of the positive and negative signal, the input power of the detector can be determined by the typical performance characteristics curves in the ADL6012 data sheet. Lastly, accounting for the attenuators, antennas, and free space path loss, the peak output power of the MG-4 can be accurately determined. At 60 cm centered from the MG-4, the ADL6012 output a 660 mV differential voltage. Using the typical application curves in the data sheet, this corresponds to a 4.4 dBm input power into the ADL6012. Accounting for the attenuators, receiving antenna, and free space path loss, the transmitted peak power of the MG-4 is 98.17 dBm (6.56 MW). This is in the expected output power range of the MG-4.
5:10pm - 5:30pm
High Power Microwaves: 5
Compact 60kV High Voltage Capacitor Charger for UWB Electromagnetic Pulse Generator
Chung-Ang University, Korea, Republic of (South Korea)
In this paper, a portable 60kV high-voltage capacitor charger for ultra-wideband electromagnetic pulse generator based on a 24V battery was described. The HVCC should charge storage capacitors up to breakdown voltage(about 55kV) of spark gap switch inside Marx generator of the ultra-wideband electromagnetic pulse generator at 100Hz repetition rate. It should be considered not only the operation specification, but also size and weight for portability, nonetheless current burden on the used components is relatively large because of low input voltage. In addition, there are other difficulties such as the voltage stress of each components and isolation from other parts like grounded case. To satisfy the requirements, a parallel loaded resonant converter which operates as high-efficiency and high-frequency and an output rectifier designed by modifying the basic Cockcroft-Walton voltage multiplier(CWVM) were applied. The parallel loaded resonant converter operating at above resonant frequency was designed with a small value of parallel resonant capacitor to reduce reactive power, crest factor of the resonant current, and conduction loss. Also, proper snubber capacitor design is applied to reduce turn off switching loss. The modified CWVM is composed of two symmetrical CWVMs charged in parallel by a center-tapped transformer and storage capacitors inside the CWVMs are connected in series to the load. With this structure, it can be alleviated the voltage stress and maximum voltage potential. Therefore, it significantly reduces the difficulty of selecting components, design of the high voltage transformer and considering insulation when manufacturing actual system. In addition, it can be operated through very simple sensorless control method, only needs the information of the time to charge the load capacitor once and repetition rate, due to the characteristics of the designed resonant converter, such as a current source characteristic and inherent maximum voltage limit. Between the HVCC and Marx generator, the conductorless high voltage cable is connected to replace the isolation resistor to block a noise generated by UWB EMP, and to limit the excessive charging speed. Finally, the HVCC was actually implemented as small(120*120*245mm) and lightweight(4kg). Various experiments with 3.2nF and 8.4nF load capacitors equivalent to the sum of storage capacitors in the Marx generator were conducted. Also, it is verified that the HVCC can charge to 62kV and be inherently limited due to the characteristic of the designed converter without any control. Finally, it was verified by the experimental result with the actual Marx generator load that the HVCC repeatedly charge over 50kV at 100Hz repetition rate.
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