Conference Agenda

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).

Session Overview
Date: Wednesday, 22/June/2022
7:15am - 8:15amBreakfast
Location: Ballroom AB
7:15am - 8:15amAuthors' Breakfast
Location: 300AB
9:30am - 10:00amCoffee Break
Location: Ballroom AB
10:00am - 12:00pmRepetitive Pulsed Power
Location: Ballroom C
Session Chair: Jacob Stephens, Texas Tech University
10:00am - 10:20am
Repetitive Pulsed Power: 1

Spark Gap with integrated triggering Laser

J. C. Pouncey

Naval Surface Warfare Center Dahlgren Division, United States of America

The use of pulsed lasers to trigger the operation of spark gap switches has a long history in pulsed power applications [1]. However, the application of this technology to compact low-energy modulators has been hampered by the size and complexity of the typical laser and optical systems. In previous work [2], the author described early experiments using a commercial diode-pumped solid state micro-laser to trigger pressurized spark gap switches. The small size of this laser made it feasible to integrate the laser directly into the body of the spark gap switch, thus reducing the complexity and providing improved ruggedness. However, the laser used in the initial experiments featured an integrated pump diode, which requires driving from a low-voltage electronic circuit. Integrating this laser directly into the spark gap would negate the principal benefit of laser triggering: the galvanic isolation of the triggering system from the high voltage circuitry of the modulator. This challenge has been addressed through a configuration in which the pump laser is fed to the solid-state laser resonator via an optical fiber. Since the pump is several orders of magnitude lower in power than the pulse from the resonator, efficient coupling through a fiber is greatly simplified compared to attempting to deliver the high-power trigger pulse through it. This configuration retains the close coupling of the laser resonator with the switch, while enabling the remote location of the low-voltage pump laser diode. An experimental switch has been constructed according to this configuration, and preliminary test results have validated the usefulness of this concept for the triggering of switches in compact modulators.

[1] A. H. Guenther and J. R. Bettis, "A review of laser-triggered switching," Proc. IEEE, vol. 59, no. 4, pp. 689-697, 1971.

[2] J. C. Pouncey and J. M. Lehr, "Triggering of Pressurized Gas Switches With a Class I Laser," in IEEE Transactions on Plasma Science, vol. 48, no. 7, pp. 2531-2537, July 2020

Distribution Statement A. Approved for public release. Distribution is unlimited.

10:20am - 10:40am
Repetitive Pulsed Power: 2

COBRA DANE Radar Transmitter Group Replacement

M. Kempkes, T. Hawkey, L. Jashari, K. Vaughan, Y. Francis, M. Gaudreau, R. Simpson

Diversified Technologies, Inc., United States of America

In 2019, Diversified Technologies, Inc. (DTI) delivered a transmitter group replacement (TGR) for the COBRA DANE ground-based radar facility at Eareckson Air Station, Shemya Island, Alaska. This individual L-Band transmitter group is part of the twelve transmitter groups housed at the facility. Each transmitter group energizes, controls, and protects eight high-power, ring-bar type traveling wave tubes (TWTs). Individual RF outputs from each tube are input to a space-fed phased array antenna. At the system core is the modulator which manages the operation of high-speed solid-state opening switches, tube filament/grid supplies, and grid switch for each of the eight TWTs in the group; minimizing the impact of any single TWT failure on the group’s performance.

The Group Controls Cabinet houses the Programmable Logic Controller (PLC) with graphical interfaces provides enhanced control, fault handling and diagnostic capabilities thereby increasing overall system sustainability and maintainability. A Power Distribution Unit feeds the group’s two high voltage power supplies (HVPSs) which power the Capacitor Bank. The Capacitor Bank feeds the modulator opening switches to provide the full beam current for the group of 8 TWTs.

The Cobra Dane TGR effort was built for the USAF under subcontract to Raytheon Intelligence and Information Systems. This unit is the first group upgrade for the replacement of all 12 TWT groups in the radar (96 TWTs total). The contract for the remaining 11 Groups was awarded directly to DTI by the USAF in September, 2020.

10:40am - 11:00am
Repetitive Pulsed Power: 3

Microscale Gas Breakdown for Microwave Fields: Theory and Simulation

S. Mahajan1, A. M. Loveless1, A. Semnani2, A. Venkattraman3, A. L. Garner1

1Purdue University, West Lafayette, IN 47906 USA; 2The University of Toledo, Toledo, OH 43606 USA; 3University of California, Merced, Merced, CA 95343 USA

Several studies have utilized theory and particle-in-cell (PIC) simulations to examine the unification of field emission and Townsend avalanche for DC gas breakdown in microscale gaps [1]. While similar techniques have been used to study field emission driven microscale gas breakdown for radiofrequency (RF) and microwave (MW) fields [2,3], these studies have not applied the asymptotic approaches used to derive closed form solutions for DC microscale gas breakdown [1] to obtain scaling relationships between pressure, frequency, and gap distances for AC fields.

This study will use PIC and theory to characterize breakdown conditions for RF and MW conditions for various pressures, frequencies, and gap distances. Following previous studies [2,3], we incorporate field emission and collisional effects into the force law for the theory. We perform PIC simulations using the code XPDP1, which is one-dimensional in space and three-dimensional in velocity and modified to incorporate field emission [1], to determine breakdown voltages under various conditions to benchmark the theory and to elucidate particle behavior, most notably charge density and ion drift velocity, for incorporation into the theory. Specifically, we use theory and simulation to characterize critical scalings, most notably pd and f/p, where p is the pressure, d is the gap distance, and f is the frequency, for gap distances from 100 nm to 10 µm and frequencies from 0.1 to 10 GHz. Modifying the integration of field emission into the MW breakdown theory [2,3] by using approach developed previously for DC [1] enables us to perform asymptotic analyses in the limits of low (i.e., field emission) and high ionization (i.e., Townsend avalanche) to determine the implication of the dominant breakdown mechanism on the scalings mentioned above. Implications on device operation, plasma parameters, and extensions to larger devices will be discussed.

1. A. L. Garner, A. M. Loveless, J. N. Dahal, and A. Venkattraman, “A tutorial on theoretical and computational techniques for gas breakdown in microscale gaps,” IEEE Trans. Plasma Sci., vol. 48, pp. 808-824, 2020.

2. M. U. Lee, J. Lee, J. K. Lee, and G. S. Yun, “Extended scaling and Paschen law for micro-sized radiofrequency plasma breakdown,” Plasma Sources Sci. Technol., vol. 26, 2017, Art. no. 034003.

3. A. Semnani, A. Vankattraman. A. A. Alexeenko, and D. Peroulis, “Frequency response of atmospheric pressure gas breakdown in micro/nanogaps,” Appl. Phys. Lett., vol. 103, 2013 Art. no. 063102.

11:00am - 11:20am
Repetitive Pulsed Power: 4

Synthesis of Pulsed Forming Systems for Electromagnetic Manufacturing Process

D. Kaushik, J. T. Meledath

Indian Institute of Science Bangalore, India

Electromagnetic(EM) manufacturing systems utilize an intense transient current pulse generated by discharging of a pulsed power source into the tooling coil (actuator coil) through a suitable closing switch. This induces strong eddy currents in the workpiece and their interaction with the current flowing through the tooling coil produces the necessary force required for the workpiece deformation. Electromagnetic manufacturing has wide range of applications for processes ranging from electromagnetic forming, magnetic pulse welding, electromagnetic crimping, embossing, deep metal drawing, sheet metal sheering etc. to name a few.

The essential components of a manufacturing system consist of a suitable pulsed power source, tooling coil, die and the workpiece. The essential figure of merit that affects the deformation in the workpiece is the embedded features of the magnetic pressure waveform. The tooling coil produces the necessary magnetic pressure on the workpiece and its geometrical configuration is responsible for the spatial distribution of the magnetic pressure on the workpiece. The parameter of the pulsed power source controls the temporal behavior of the magnetic pressure on the workpiece. Finally, the die design determines the final shape of the deformed workpiece. Therefore, there exists a limiting approach for the design of the pulsed electromagnetic forming system for the workpiece depending on the final objective of the process. If the goal is to form shallow features on the workpiece such as free forming process etc., the essential figure of merit is the temporal variation of pressure profile and the maximum pressure on the workpiece. However, if significant deformation is required where the workpiece is made to impact a die in processes like embossing or magnetic pulse welding, which produces substantial impact pressures, the essential figure of merit in this case is the maximum velocity or the impact velocity of the workpiece. Nonetheless, the determination of the temporal behavior of magnetic pressure profile on the workpiece becomes the starting point.

The spatial features of the magnetic pressure on the workpiece are fixed once the geometrical assembly has been finalized. However, the pulsed electromagnetic manufacturing methods provide a high degree of flexibility for the control of temporal features of the magnetic pressure acting on the workpiece. The paper describes a novel approach to design and synthesize the pulsed power systems starting from either the target pressure profile or the velocity profile of the workpiece, and then presents a suitable methodology for synthesizing the pulsed power circuit. A suitable topology of circuit elements is first defined, and then important design parameters are identified for the synthesis of the pulsed circuit. Curve fitting methods along with unconstrained optimization techniques are used to find the optimized values of design parameters. The deformation in the workpiece is also simulated for the target and computed profiles and the designed pulsed power system is experimentally validated for the given tooling coil and workpiece system under consideration. The results obtained are found to be in good agreement for the designed parameters.

11:20am - 11:40am
Repetitive Pulsed Power: 5

Acoustic energy from exploding wire generated chemical reaction

T. Frost, B. M. Novac, P. Senior

Loughborough University, United Kingdom

The exothermic chemical reaction between aluminium and water is well known for a long time. However, this presentation will focus on a study representing the first stage of development of a repetitive exploding wire-based pressure source for industrial applications. The practical arrangement and the diagnostic tools will both be presented, together with data showing amount of chemical energy transferred to the acoustic pressure wave.

11:40am - 12:00pm
Repetitive Pulsed Power: 6

Explosive Pulsed Power: Milling operation limits of PBX 9501 and PBX 9502

E. Weeks1, J. Williams1, R. Clark1, S. Watkins1, R. Albin1, J. Dickens1, J. Mankowski1, J. Brikman2, A. Neuber1

1Texas Tech University, Lubbock, TX; 2CNS Pantex, FM2373 and HWY 60

Explosive-driven pulsed power performance benefits from modern polymer-bonded explosives. Owing to the explosives’ fast reaction, high voltage pulses with microsecond to nanosecond duration may be produced. In the fabrication of explosively driven devices, high precision in the dimensional shape is required in practical application, and high machining speeds are desired. The range of allowable machining speeds is dictated by the US DOE-STD-1212-2019 with general coverage of all explosive materials. As previously demonstrated for lathing, the machining of the new polymer-bonded explosives may be safely exceeded. To establish new, safe boundaries, the thermalresponse of PBX 9501/9502 under conventional milling methods is studied. The presented work focuses on face milling performed with dry machining on a CNC, remote-controlled milling machine. Spindle RPM, feed rate, step size, and depth of cut were chosen as the primary parameters of interest. While pushing some parameters a factor 4 higher than presently allowed in the standard, the temperature was monitored via high-speed IR videography and with a K-type thermocouple inserted into the endmill’s through coolant holes. A 6-axis force sensor mounted beneath the HE samples records operational forces and torques. Force and temperature curves are examined as a function of time, revealing behavioral differences for each material. Overall, milling regimes exist outside of DOE-STD-1212-2019 for which milling temperatures remain well below the HE critical temperatures. Characterization by the material removal rate allows for the generalization of the temperature trends and, more significantly, identification of milling regimes that maintain low temperatures and low cutting forces while allowing for relatively quick milling cycles. The analysis of empirical equations enables assessing the theoretical limits of the different parameters.

10:00am - 12:00pmBiomedical and Applications
Location: 301B
Session Chair: Ram Anand Vadlamani, Virginia Tech
10:00am - 10:20am
BioMed and Applications: 1

Pulsed Electric Field Activation of Platelet Rich Plasmas with Different Levels of Platelet Enrichment and Red Blood Cell Content

B. Neculaes1, A. Garner2, E. Longman2

1GE Research, Niskayuna, NY, United States of America; 2Purdue University, West Lafayette, IN, United States of America

Ex vivo platelet activation is being explored for a variety of regenerative medicine and wound healing applications. Activating the platelets releases multiple proteins and growth factors with key roles in the wound healing cascade. Platelet rich plasma (PRP) is typically obtained by centrifugation from the whole blood drawn from the patient. Bovine thrombin, a biochemical agent derived from animal sources, is then used in the clinic as the state of art platelet activator. The activated PRP, called platelet gel, is applied topically on the wound to be treated. Several studies have examined pulsed electric fields as a physically based method for platelet activation with several key advantages over bovine thrombin, including an easier workflow, the ability to standardize the method, reduced cost, enhanced tunability, and independence from animal sources that may cause immune response. Pulsed electric fields of various pulse durations [1] and delivery modality (capacitive or conductive coupling; various concentrations of extracellular calcium) [2] have been successfully used for ex vivo platelet activation in several biological matrices, including whole blood [3] and platelet rich plasma with red blood cell (RBC) content. This study presents the first results of pulsed electric field activation using three types of platelet rich plasmas from four human donors – one with RBC content and two others with minimal RBC content. Two types of microsecond pulsed electric fields have been used in this study, along with negative (no activation) and positive (activation using bovine thrombin) controls. Experimental results confirm growth factor release with pulsed electric fields for all three types of PRP – opening the door for wide clinical adoption of this novel pulsed power based biomedical approach.

[1] A. L. Garner, A. S. Torres, S. Klopman, and B. Neculaes, “Electrical stimulation of whole blood for growth factor release and potential clinical implications,” Med. Hypotheses, vol. 143, 2020, Art. no. 110105.

[2] A. L. Garner, A. L. Frelinger III, A. J. Gerrits, T. Gremmel, E. E. Forde, S. L. Carmichael, A. D. Michelson, and V. B. Neculaes, “Using extracellular calcium concentration and electric pulse conditions to tune platelet-rich plasma growth factor release and clotting,” Med. Hypotheses, vol. 125, pp. 100-105, 2019.

[3] B. Neculaes, A. L. Garner, S. Klopman, C. Morton, and A. S. Torres, “A multi-donor ex vivo platelet activation and growth factor release study using electric pulses with durations up to 100 microseconds,” IEEE Access, vol. 9, pp. 31340 – 31349, 2021.

10:20am - 10:40am
BioMed and Applications: 2

Analysis of the Role of Cellular Heating in Microsecond Irreversible Electroporation

W. J. Milestone1, Q. Hu2, A. M. Loveless3, A. L. Garner3, R. P. Joshi1

1Texas Tech University, Lubbock, TX 79409, USA; 2Eastern Michigan University, Ypsilanti, MI 48197, USA; 3Purdue University, West Lafayette, IN 47906, USA.

Irreversible electroporation (IRE) involving tumor ablation presents a minimally invasive treatment and has found a niche in oncological applications. It has proven to be a safe and effective procedure for treating many unresectable tumors. However, the use of a series of high frequency sinusoidal bipolar electric pulses, in the context of cellular drug delivery and/or irreversible electroporation, has not been studied to the best of our knowledge. This scheme, similar to the High Frequency Irreversible Electroporation (HFIRE) protocol, could prove to be of utility and synergistic effects of local membrane heating might well be beneficial in the context of this long wavetrain. In the present simulation study, two aspects of interest will be probed: (i) the role of cell heating in possibly promoting the successful uptake of drugs for treatment, and (ii) the possible synergistic interplay between the electric field and local membrane heating in reducing the required electroporation threshold.

In this work, membrane electroporation will be simulated based on a Smoluchowski continuum analysis discussed elsewhere by our group, together with spatio-temporal heating due to the power dissipation from the external bi-phasic source. We will consider two-dimensional transient heat flow with azimuthal symmetry in a single spherical cell. The following aspects will be analyzed and discussed in this presentation: (i) Changes induced by including heating, especially effects on pore formation dynamics. (ii) Quantitative assessment of the magnitude of heating caused by the applied electric fields and its dependence on wavetrain and field characteristics. This could define safe-operating limits and/or provide guidance towards optimum parameter space. Given that the vast parameter space depends on multiple factors, including cell size, pulse characteristics, electrical and thermal parameters of the biological system, applied waveforms, and number of pulses, only a few test cases will be probed. (iii) The present simulations will allow predictions and mechanistic insights into the level of electric field threshold reductions possible due to synergistic heating. (iv) And finally, the possibility of establishing large thermal gradients at the membrane for thermo-diffusive transport will also be quantitatively assessed.

10:40am - 11:20am
BioMed and Applications: 3

Enhanced inactivation of Gram-negative bacteria using Gram-positive antibiotics and nanosecond electric pulses

R. A. Vadlamani1, A. Dhanabal2, D. A Detwiler3, R. Pal1,2, J. McCarthy3, M. N Seleem1,2, A. L Garner2

1Virginia Tech; 2Purdue University; 3Nanovis

Physically disrupting microorganism membranes with electric pulses renders the resistance mechanisms that inhibit or excrete antibiotics inert, reducing the antibiotic dosages required and making ineffective antibiotics effective. The growing threat of antibiotic resistant infections combined with a lack of drugs in the discovery pipeline necessitates novel ways for enhancing existing antibiotic effectiveness [1]. Nanosecond electric pulses (NSEPs) can make Gram-positive antibiotics, which are abundant, effective against Gram-negative resistant strains of bacteria, for which new and effective medicines are sorely lacking, on a sufficiently short timeframe to prevent resistance mechanisms from developing. We demonstrate the synergistic inactivation of a Gram-positive (Staphylococcus aureus) and two Gram-negative (Escherichia coli, and Pseudomonas aeruginosa) bacteria by combining various antibiotics with different mechanisms of action with 222 30 kV/cm or 500 20 kV/cm, 300 ns duration electric pulses (EPs) [2], energy matched [3] but selected such that the lower electric fields had minimal impact on viability, but reacted synergistically in combination with antibiotics. Combining NSEPs with antibiotics induced several log-reduction of colony forming units for antibiotics that induced no inactivation following 10 minutes of exposure in solution without NSEPs. Staphylococcus aureus inactivation improved compared to EPs alone when we combined 2 mg/L or 20 mg/mL of rifampicin with the 30 kV/cm EPs; however, only a few of the other combinations enhanced inactivation. E. coli inactivation improved compared to EPs alone by combining either EP pulse train with 2 mg/L or 20 mg/mL of mupirocin or rifampicin or by combining the 30 kV/cm EPs with either 2 mg/L or 20 mg/mL of erythromycin or vancomycin. These results indicate that EPs can make Gram-positive antibiotics efficient for inactivating Gram-negative bacteria.

[1] D. S. Davies and E. S. Verde, “Antimicrobial resistance,” Search Collab. Solut. World Innov. Summit Health Doha, pp. 1–36, 2013.

[2] A. Vadlamani, D. A. Detwiler, A. Dhanabal, and A. L. Garner, “Synergistic bacterial inactivation by combining antibiotics with nanosecond electric pulses,” Appl. Microbiol. Biotechnol., vol. 102, no. 17, pp. 7589–7596, 2018.

[3] K. Schoenbach, R. Joshi, S. Beebe, and C. Baum, “A scaling law for membrane permeabilization with nanopulses,” IEEE Trans. Dielectr. Electr. Insul., vol. 16, no. 5, pp. 1224–1235, Oct. 2009.

11:20am - 11:40am
BioMed and Applications: 4

Using intense pulsed electric fields for the sterilization of solid pre-packed food – the design and preliminary testing of a practical MV-class system

M. Woodyard, B. Novac, P. Senior, J. Stobbs

Loughborough University, United Kingdom

A pulsed power MV-class system for generating intense pulsed electric fields in a very large volume of water was designed, manufactured and tested. This is a first and essential step towards the proof-of-principle demonstration of a novel technique for the non-invasive sterilisation of pre-packed food. The pulsed power system, based on MV Tesla transformer technology, is capable of producing pulsed electric fields in excess of 100 kV/cm in a massive volume (≈1 L) of water. The electric field distribution in the processing volume is obtained using a commercially available electrostatic solver, benchmarked using an electro-optic Kerr-effect assembly. The paper presents a detailed analysis of the unique processing unit and theoretically explores a possible scenario related to processing pre-packed food.

11:40am - 12:00pm
BioMed and Applications: 5

Resonant Charging Circuit for a Semiconductor-based Marx Generator for an Electropoation Device

M. Sack, D. Herzog, J. Ruf, G. Mueller

Karlsruhe Institute of Technology, Germany

Electroporation devices for the treatment of plant material in a continuous flow may employ a Marx circuit featuring parallel charging and a complete discharge of the capacitors during each pulse. Thereby, the use of semiconductor switches rather than spark gap switches allows for a modern design without the need of recurring maintenance of the spark gap switches. However, the use of semiconductor switches demands for an adaptation of the circuit to the properties of these switches being able to operate at lower voltage and current but higher pulse repetition rate compared to spark gap switches. For such a design, resonant charging turned out to be of advantage because it combines a fast energy transfer from a DC-link capacitor as part of the power supply to the stage capacitors of a Marx generator with a charging circuit having no active switches. Moreover, it enables an increase in the charging voltage by a factor of approximately two with respect to the DC-link voltage.
An 8-stage Marx circuit with a stage voltage of 1 kV has been set up to study resonant charging. Its charging path has been equipped with current-compensated chokes having a low inductance during charging and a high inductance for transient insulation of the stages during the pulse generation. The charging circuit has been designed for a peak current of 70 A and a charging time of 800 µs. A separate inductance between the DC-link capacitor of the power supply and the generator serves as the inductive component for the resonance circuit. As pulse switches IGBTs have been employed. In the course of the charging process, they serve as opening switches allowing for fine tuning of the charging voltage in repetitive operation. The generator has been operated either with a ground connection at its negative output terminal or grounded at its center to deliver a ground-symmetric output voltage. In both cases the magnetic energy stored inside the current-compensated chokes has been either degraded or recycled to prevent the cores from saturation. In the latter case, measurements revealed oscillations in a resonant circuit comprising the stray capacitance of the current-compensated chokes. A series diode avoids these oscillations. The paper describes selected details of the circuit design and presents measurements of the charging process.

12:00pm - 1:30pmLunch (on your own)
1:30pm - 3:00pmIPMHVC Plenary Lecture - R. Joshi
Location: Ballroom EF
Session Chair: Allen Garner, Purdue University
1:30pm - 2:30pm

Modeling electric-field driven nonequilibrium phenomena for applications to pulsed power, electron beam generation, transport in materials, and electromanipulation for biomedicine

R. P. Joshi, M. Brown, W. Milestone, M. Sanati, J. Mankowski, J. Dickens, A. Neuber

Texas Tech University, United States of America

This talk will briefly touch upon the many innovative applications involving nonequilibrium and ultrafast processes in areas of pulsed power and high power microwaves driven by high electric fields. Many applications either involve the use of high electric fields to help enhance system currents or power generation (as in high power microwave systems), or to take advantage of non- equilibrium transient phenomena which can produce larger responses (e.g., the transient drift velocity overshoots in photoconductive switches), or be used to curtail the role of slower processes (such as dynamic shielding based on charge transport that typically require longer times), or help attain high internal electric fields in a targeted manner through robust displacement currents (e.g., the field penetration into sub-cellular organelles in biomedical applications). It is, therefore, possible that somewhat different system responses and outcomes can be achieved due to the ultrashort temporal regimes, or under the influence of high local electric fields. This operating domain can often trigger novel physics, or lead to effects dominated by nonequilibrium processes, or simply bring certain mechanisms to the forefront that might otherwise have remained negligible under near-equilibrium conditions.

This presentation will focus on our efforts at modeling and simulations of phenomena dominated by high electric fields, with inclusion of the transient processes. The goal is towards a better understanding for successful and more efficient applications to pulsed power, high power microwave generation, and biomedicine. The talk would include aspects of electron emission, outgassing in high power machines, operation of ultrafast photoconductive switches, materials engineering to curtail deleterious effects, electrochemotherapy and possible nerve stimulation, etc. The connection between engineering and the underlying science will also be discussed that can then lead to optimization.

3:00pm - 3:30pmCoffee Break
Location: Ballroom AB
3:30pm - 5:30pmHigh Voltage
Location: Ballroom C
Session Chair: Howard Sanders, Sanders Pulsed Power LLC
3:30pm - 3:50pm
High Voltage: 1

Influence of Low Pressure on Thermal Limit of MVDC Power Cables Used in All Electric Aircraft

A. Azizi1, M. Ghassemi1, J. Lehr2

1Virginia Tech, United States of America; 2University of New Mexico, United States of America

An electric power system (EPS) with high power delivery and low system mass is required for wide-body all-electric aircraft (AEA). Cables are an essential component of this future EPS. The pressure at the cruising height of a wide-body aircraft is around 18.8 kPa. At that pressure, heat transfer to the ambient air by convection is strongly limited, so the temperature field distribution across the aircraft cables is expected to be different from atmospheric pressure. The temperature field across the cable depends on the velocity field of the ambient air, which is a function of pressure and temperature. Also, to obtain the electric field of the DC cables in the electric aircraft power system, the conductivity of the insulation, a function of temperature and electric field, should be calculated. Therefore, a coupled multi-physics study should be conducted to calculate the temperature field and electric field across the cable. In this paper, a 5 kV DC cable is studied at 18.8 kPa pressure to compare the cable's temperature field and electric field at low pressure to the atmospheric pressure. The voltage level considered was resulted from our previous studies where we proposed new EPS architectures for a wide-body AEA. Moreover, the maximum permissible flowing current of the cable is investigated at the pressure of 18.8 kPa regarding the thermal limits of the cable. It is shown that at low pressures the temperature of the cable is highly increased compared to atmospheric pressure, so the maximum permissible flowing current is lower than the rated current.

3:50pm - 4:10pm
High Voltage: 2

An innovative approach to the design of medium voltage power electronics printed circuit-boards

Q. Yang, C. Diendorfer, D. Nath, M. Steurer, G. C. Montanari

Center for Advanced Power Systems, Florida State University, United States of America

Going towards maximization of power density and dynamics, the supply of electrical and electronics components in industrial, electrified transportation and renewable electrical assets is shifting from sinusoidal AC to modulated AC and DC, involving voltage and load transients.

Voltage is increasing to the MV range so that power electronics boards must be designed to withstand, for the specified operation life, high electric fields and temperatures. Very fast switching time and high modulation and carrier frequencies have to be also managed.

This determines electrical, thermal and mechanical stress profiles which can change significantly with supply voltage and time. They can affect (increasing) electrothermal and mechanical aging rate regarding both intrinsic and extrinsic aging factors.

As an example, the electric field in bulk insulation defects or on the PCB surface can incept partial discharges, PD, for some stress conditions, with different PD amplitude and repetition rate from AC to DC. This impacts on extrinsic aging rate, so that life reduction can be dramatic even if PD activity would be discontinuous.

This paper introduces an innovative approach to power electronic board design which should allow an optimized design of PCB insulation systems as regards their reliability, life, shape and dimensions/weight, taking into account the risk of generating extrinsic aging phenomena. The so called “three-leg approach” is based on the comparison and match of results coming from electric stress profile simulation, discharge modelling and partial discharge, PD, measurements under the type of waveform that a PCB can experience, specifically modulated AC and DC. It consists of extracting the information of maximum bulk and surface (tangential) electrical stress (field) at operating temperatures, comparing them with models for partial discharge inception that associated the stress to PD likelihood and linking such results with PD measurements (particularly the partial discharge inception voltage, PDIV). This would provide a PD-free design allowing inference on connector technology and shape, as well as quantities as creepage and clearance. The focus in this paper is describing how to deal with the first leg approach on a 5 kV PCB, showing electric field simulation results and explaining how discharge modelling and PD measurement will complete the whole optimized design.

4:10pm - 4:30pm
High Voltage: 3

Breakdown Characteristics of Printed Circuit Board Based Transformer Windings

R. E. P. Frost1, P. L. Lewin2

1QinetiQ, United Kingdom; 2University of Southampton, United Kingdom

Further to work presented at IPMHVC 2018 [1], this paper examines printed circuit board (PCB) based transformer winding technology that can be used in a new generation of UHV power supply. Transformer windings printed on PCBs have several advantages over conventional windings. In addition to being robust and convenient to handle, they are easy, and relatively cheap, to manufacture. For these reasons they have enjoyed limited use in low voltage applications.
In the last few decades, PCB windings have begun to be used in HV applications. James Cross took advantage of their compact size, and ease with which power electronics could be mounted to them, when designing his 750 kV insulated core transformer [2]. However, despite their increasing use in HV applications, until now there has not yet been a comprehensive investigation into the voltage handling limits of PCB windings. This paper seeks to redress this shortage.
To do this an investigation was carried out, which began by dividing any potential winding into separate areas in which breakdown may occur, and then simulating the electric field around each one in order to identify areas of increased electrical stress. Possible breakdown mechanisms are discussed based on these results.
Practical experiments were then undertaken to verify the results of these simulations. Experiments were also carried out after the initial breakdown occurred, in order to determine the effect that the solder mask has on breakdown voltage. It was shown by simulation and experimental results that adjacent tracks, separated by 0.5 mm, could withstand a voltage potential of several kilovolts.
This research suggests that PCBs are an ideal technology for constructing transformer windings, and provides an insight into a possible future of HV power supply design. Future publications concerning this project will focus on the effects that the distance between tracks, operating frequency, and environmental factors have on the breakdown voltage between windings.

[1] R. E. P Frost, J. A. Pilgrim, P. L. Lewin, M. Spong, "An Investigation into the Next Generation of High Density Ultra High Voltage Power Supplies", Int. Power Modulators and High Voltage Conference (IPMHVC), 2018.
[2] J. D. Cross, Modular High Voltage Power Supply with Integral Flux Leakage Compensation, US6026004A, 1998.

4:30pm - 4:50pm
High Voltage: 4

Reliable, Low-Jitter 100-kV Trigger Generator

R. E. Beverly III

R. E. Beverly III and Associates, United States of America

Large pulsed power systems require multiple trigger generators that are synchronous and accurate. Spark gaps having up to 200 kV across the electrodes are often utilized. Precise system triggering requires a comparable open-circuit peak voltage for low jitter operation and high certainty of gap commutation. "Low jitter" is typically σ ≤ 3 ns relative to a fast rise, 5-V command signal. One standard deviation σ is calculated using sampled delay-time measurements, where td is defined as the time between the leading edges of the input command and generator output signals.

The trigger generator must be highly reliable. Large systems carry enough energy to damage the load or other components even if one sub-module unintentionally pre-fires. Large systems are also degraded by misfires because most experiments have specific requirements for amplitude and temporal shape of the load current. Collectively these constraints place severe demands on trigger generators.

In simplest terms, the problem is one of amplification of the command pulse with a power gain of ~85 db. In practice, this must be done in multiple steps. In our approach, the command pulse is amplified to ~1 kV using a proprietary solid-state driver. Voltage multiplication is accomplished by a four-stage inductive adder that provides a fast-rise (17 ns) trigger pulse for a highly-compact (21 kg), 3-stage Marx generator with 19 J of stored energy. The first stage is configured as a trigatron with a surface discharge trigger.

The load (field-distortion switch, railgap, etc.) is connected through either a 6-m RG-220/U or 21-m RG-218/U coaxial cable. When driving a cable matched load (50 Ω), the peak voltage is ≈100 kV with a rise time <5 ns and e-folding time ≈150 ns. A peak voltage of 180 kV, rise time of <3 ns, and e-folding time of 190 ns are observed with a higher-impedance load (190 Ω). The self-break fraction (f) is defined as the ratio of Marx generator operating voltage (Vop) and median self-breakdown voltage (Vsb), where Vsb is a function of the internal gas pressure. td decreases rapidly to a lower asymptote as f→1 and σ < 4 ns when f ≥ 0.83. The probability of a pre-fire is extremely low as long as f ≤ 0.90, therefore the trigger generator affords both low jitter and high reliability when operating within the recommended range 0.85 ≤ f ≤ 0.89.

Compared with other commercially-available trigger generators, our design does not rely upon bulky and difficult-to-obtain thermionic devices (e.g. thyratrons). The design is fully scalable to higher voltages by incorporation of additional Marx stages and scalable to higher energies by increasing the number of capacitors per stage. The output polarity may be changed by the user. The control console accepts both fiber-optic and electrical command inputs. The trigger generator is largely impervious to load faults when properly coupled. The system is designed for long life with minimal maintenance.

4:50pm - 5:10pm
High Voltage: 5

Custom electrostatic probe diagnostics

M. LaPointe1, B. Esser1, I. Aponte1, Z. Cardenas1, J. Dickens1, J. Mankowski1, J. Stephens1, D. Friesen2, N. Koone2, D. Hattz2, C. Nelson2, A. Neuber1

1Texas Tech University, United States of America; 2Pantex, Amarillo Tx. United States of America

A custom electrostatic probe design for the mapping of surface charge is presented. The coaxial geometry capitalizes on capacitive voltage division, allowing for a simple design and rapid prototyping abilities. Previously a coaxial probe was designed with a 9.4 mm diameter inner conductor to reduce field enhancements to surpass commercially available probe thresholds of +/- 20 kV. Designing the inner conductor to reduce field enhancements that could reach +/- 30 kV at 1 cm distances in air resulted in a reduced resolution compared to commercially available probes when compared directly without post-processing. This work focuses on an updated design where the inner conductor diameter was reduced to 1.6 mm, yielding an improved resolution by a factor of approximately six. The outer conductor was wrapped around the center conductor to keep the field enhancement low, leaving only an ~ 0.5 mm insulating gap between the outer, grounded conductor and the center. This effectively created a hemispherical ending with a 9.4 mm diameter since the potential difference between inner and outer conductors is only on the order of a few volts.

A post-processing procedure using an Inverse Wiener filter, often used in image processing, deconvolves the custom probe’s response and regains some of the resolution lost through the necessarily large distance from the charged surface. A COMSOL finite element simulation was used to find the spatial transfer function needed for the post-processing correction. Surface charge mapping was performed for both PTFE and Acrylic, focusing on how charging polarities and different humidities affect charge distribution to determine a relationship between charge decay and unique charge distributions. For instance, using the same triboelectric charging technique for PTFE and Acrylic resulted in negative and positive surface charging, respectively, as expected from the triboelectric series. Across the measured RH humidity range, ~ 10 to 60%, Acrylic had a slower decay rate than PTFE, which may be primarily driven by the initially higher surface potential magnitude observed for PTFE under triboelectric charging.

5:10pm - 5:30pm
High Voltage: 6

Improved Manufacturing Process for High Voltage Pulsed Diodes

A. Usenko1, A. Caruso1, S. Bellinger2

1University of Missouri-Kansas City, United States of America; 2Semiconductor Power Technologies, Manhattan, KS, USA

DSRDs - Drift Step Recovery Diodes are used as opening switches for pulse generators since 1960s. Deep diffusion into a thinned wafer have been mostly used for the DSRD fabrication. The diffusion-based process has limitations in: (1) doping profile optimization, (2) diode side surface termination, (3) diode side surface passivation, (4) stacking on wafer level. These features limit final diode performance. (1) long voltage rise time, (2) and (3) low diode breakdown voltage, (4) heavy labor at die assembly into stacks.

We have suggested and tested new DSRD fabrication scheme where (1) deep diffusion replaced by epitaxy with desired doping profile, (2) diode side termination done by anisotropic etch instead on mechanical sawing, (3) diode side passivation by silicon dioxide instead on polyimide, (4) stacking on wafer level.

TCAD simulation predicted an optimal DSRD doping profile to reach the shortest rise time on a load. The predicted profile is different from profile obtained by diffusion (complementary error function). The predicted profile can be copied into silicon by controlling dopant flow during epitaxy. We have modified epitaxy tool to achieve desired profile and successfully grown near 200-micron thick epitaxial layer. This is drastically different from known attempts to fabricate DSRD using non-controlled (flat) epitaxial doping profile.

In traditional DSRD technology, wafers are cut into diode dies mechanically - by sawing, waterjet, laser cut, etc. This result in termination of diodes by surface that is perpendicular to wafer surface (vertical wall). While beveled wall is preferable – it gives higher breakdown voltage. Thus, traditional DSRD has breakdown along the vertical wall - diode termination surface. Also, mechanical cutting inevitably produces cracks, up to 50 microns deep into silicon. These additionally lower the breakdown voltage. And requires chemical etching, typically in HNA – to dissolve the damaged silicon.

We have replaced mechanical cutting step by anisotropic etching of v-grooves through lithography mask. Advantages are beveled diode side termination wall and no cracks. These result in higher breakdown voltages of the diodes. Another advantage is – v-groves go only below the epitaxial p-n junction layers, but not to the bottom of silicon substrate. Therefore, wafer integrity is preserved. This gives us an opportunity to stack wafers, not individual dies. Finally, we get more then hundred times smaller number of stacking operations, i.e., better manufacturability.

Passivation in the traditional DSRD process is heavily restricted. Say, oxidation cannot be used as top, and bottom of diode dies are already covered with metal layers for Ohmic contacts. Therefore, polymer coating – polyimide or silicone used. Our v-groove diode die separation does not pose this limitation. We have option to deposit metals later in process flow. Therefore, we use thermal oxidation to passivate side surfaces of individual diodes. The silicon dioxide passivation is preferable compared to polymer coating in both, breakdown voltage and long-term device stability considerations.

DSRDs manufactured with our novel process are sent for measurement of their pulsed performance. Separate presentation will report comparison of pulsed performance between traditional and our DSRDs.

3:30pm - 5:30pmAnalytical Methods
Location: 301B
Session Chair: Amanda M. Loveless, Purdue University
3:30pm - 3:50pm
Analytical Methods: 1

Comparison of Particle-in-Cell and Continuum Simulations for RF Microscale Gas Breakdown

A. M. Loveless1, V. Ayyaswamy2, S. Mahajan1, A. Semnani3, A. L. Garner1

1Purdue University, United States of America; 2University of California Merced, United States of America; 3University of Toledo, United States of America

Understanding and accurately characterizing electron emission and gas breakdown is necessary with increasing device miniaturization. For DC voltages, Paschen’s law, which is based on the Townsend avalanche criterion, is commonly used to predict gas breakdown; however, for microscale gaps, the resulting strong electric fields at breakdown induce the release of additional electrons by field emission (FE), which considers the enhanced surface electric field due to the decreased potential barrier at the cathode [1]. Accurately predicting breakdown under these conditions requires combining field emission and Townsend avalanche. Similarly, field emission also contributes to breakdown for microscale gaps under RF and microwave fields, motivating theoretical studies and particle-in-cell (PIC) simulations [2] to account for this behavior. While effective for gaps below ~10 microns at atmospheric pressure, PIC is not computationally efficient for larger gaps due to the computational expense encountered with additional particles. Thus, this study compares RF breakdown simulations using PDP1, a 1D/3v (one-dimensional in space, three-dimensional in velocity) PIC code, to continuum simulations using SOMAFOAM [3], a finite volume framework to simulate low-temperature plasmas. The results between PDP1 and SOMAFOAM will be compared to each other and theory for various frequencies, pressures, and gap distances, particularly to assess scaling laws between these parameters in different operational regimes. The computational efficiency of the two methods and assessment to theory and experiment will be discussed.

[1] A. L. Garner, A. M. Loveless, J. N. Dahal, and A. Venkattraman, “A tutorial on theoretical and computational techniques for gas breakdown in microscale gaps,” IEEE Trans. Plasma Sci., vol. 48, pp. 808-824, 2020.

[2] M. U. Lee, J. Lee, J. K. Lee, and G. S. Yun, “Extended scaling and Paschen law for micro-sized radiofrequency plasma breakdown," Plasma Sources Sci. Technol., vol. 26, art. no. 034003, 2017.

[3] A. K. Verma and A. Venkattraman, “SOMAFOAM: An OpenFOAM based solver for continuum simulations of low-temperature plasmas,” Comp. Phys. Comm., vol. 263, art. no. 107855, 2021.

Work supported by the Office of Naval Research under Grant Number N00014-21-1-2441.

3:50pm - 4:30pm
Analytical Methods: 2

Crossed-Field Nexus Theory: Incorporating Collisions, Field Emission, Thermionic Emission, and Space-Charge

L. I. Breen1, A. M. Loveless1, A. M. Darr1, K. L. Cartwright2, A. L. Garner1

1Purdue University, West Lafayette, IN 47906 USA; 2Sandia National Laboratories, Albuquerque, NM

Understanding electron emission is vital for characterizing diode performance for numerous applications, including directed energy systems, thermionic converters, time-resolved electron microscopy, and x-ray systems. The “nexus theory” formulation may be used to predict the physical conditions where multiple electron emission mechanisms, such as thermionic, field, and space-charge limited emission, may need to be solved jointly [1]. Once nexus theory identifies such a regime, one can derive exact equations from first principles that couple the relevant physics to assess behavior. The exact model should recover the standard equations for the individual emission mechanisms under appropriate asymptotic limits [1]. Operating conditions near where these asymptotic solutions match require more complicated equations coupling the relevant mechanisms; regimes farther away from these intersections may use the simpler, well-known solutions.

A common diode design in high power applications incorporates an external magnetic field perpendicular to the electric field induced by the applied voltage. Electron trajectories in these crossed-field diodes may either cross the gap if the magnetic field is below a limiting value known as the Hull cutoff or be turned back to the cathode for magnetic fields exceeding the Hull cutoff. Above the Hull cutoff, the diode is magnetically insulated. Much as the Child-Langmuir equation characterizes planar space-charge limited current (SCLC), similar equations may be derived for the limiting current in crossed-field diodes under non-magnetically insulated [2] and magnetically insulated conditions [3]. These conditions do not strongly depend on the specific electron emission mechanism, but rather define the maximum current that may be emitted into the gap based on geometry and boundary conditions.

This presentation highlights our application of nexus theory to crossed-field diodes. We unify thermionic and field emission with the limiting current in a crossed-field diode by introducing the generalized thermal-field emission current density equation, as was previously derived for non-magnetic diodes [1]. We will next introduce collisions into the derivation of the limiting current of crossed-field diodes [2,3] to derive a collision limiting current for a crossed-field diode, equivalent to a Mott-Gurney law for non-magnetic SCLC with collisions. The implications of the transitions between these mechanisms under various conditions and the respective limits on device operation will be discussed.

1. A. M. Darr, C. R. Darr, and A. L. Garner, “Theoretical assessment of transitions across thermionic, field, and space-charge-limited emission,” Phys. Rev. Res., vol. 2, 2020, Art. no. 033137.

2. Y. Y. Lau, P. J. Christenson, and D. Chernin, “Limiting current in a crossed-field gap,” Phys. Plasmas, vol. 5, pp. 4486-4489, 1993.

3. P. J. Christenson and Y. Y. Lau, “Transition to turbulence in a crossed‐field gap,” Phys. Plasmas, vol. 12, pp. 3725-3727, 1994.

4:30pm - 4:50pm
Analytical Methods: 3

Novel techniques for deriving the space-charge limited current for nonplanar diodes

N. R. Sree Harsha, A. M. Darr, J. M. Halpern, A. L. Garner

Purdue University, United States of America

Space-charge-limited current (SCLC) is the maximum current that can flow in the steady-state operation of the diode. Characterizing SCLC is critical for understanding the behavior of various devices, including high-power vacuum devices, organic field-effect transistors, quantum diodes, n-i-n or p-i-p diodes, and photovoltaic devices [1]. The SCLC in a one-dimensional (1-D) planar diode was derived independently by Child and Langmuir over a century ago [1]. Recently, we applied variational calculus (VC) and conformal mapping (CM) to derive analytic solutions to SCLC for nonplanar diode geometries [2].

In this presentation, we review the application of VC and CM to obtain analytic solutions for SCLC for nonplanar diodes. The analytic solutions for SCLC in any orthogonal coordinate system can be obtained using VC by extremizing the total current in the gap [2]. While VC is a powerful technique to solve for SCLC, the calculations become tedious for diodes exhibiting curvilinear flow. For such geometries, we have applied CM to transform the curvilinear flow into a rectilinear flow, thereby obtaining analytic SCLC solutions [2]. We extend VC to obtain a mathematical relationship between vacuum potential and space-charge-limited potential in any orthogonal geometry [3]. The exact solutions for SCLC in two-dimensional and three-dimensional planar diodes with finite emitters are presented [3]. We also apply Lie point symmetries to derive SCLC with nonzero injection velocity in nonplanar diode geometries and describe how similar solutions may be obtained using VC. The practical importance of this flexibility and a comparison between these mathematically powerful techniques will be discussed.

[1] P. Zhang, Y. S. Ang, A. L. Garner, Á. Valfells, J. W. Luginsland, and L. K. Ang, “Space–charge limited current in nanodiodes: Ballistic, collisional, and dynamical effects,” J. Appl. Phys., vol. 129, no. 10, Mar. 2021, Art. no. 100902.

[2] A. L. Garner, A. M. Darr, and N. R. Sree Harsha, “Calculating space-charge limited current density for general geometries and multiple dimensions,” IEEE Trans. Plasma Sci., submitted.

[3] N. R. S. Harsha, M. Pearlman, J. Browning, and A. L. Garner, “A multi-dimensional Child–Langmuir law for any diode geometry,” Phys. Plasmas, vol. 28, no.12, Dec. 2021, Art. no. 122103.


This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-19-1-0101 and a Purdue Doctoral Fellowship.

4:50pm - 5:10pm
Analytical Methods: 4

Assessment of Techniques for Determining Space-Charge Limited Current for Non-planar Crossed-field Diodes

H. Wang, N. R. Sree Harsha, A. M. Darr, A. L. Garner

Purdue University

The maximum stable current that can flow in a diode, known as the space-charge limited current (SCLC), is essential for numerous applications, including nano vacuum transistors, electric thrusters, and time-resolved electron microscopy. Recently, several general approaches for deriving analytic solutions for non-planar and multidimensional diodes have been developed [1]. Crossed-field diodes (CFDs), where an external magnetic field B is applied perpendicular to the electric field, may also be characterized by a maximum current that depends on whether an emitted electron crosses the gap or turns back to the cathode [2]. Unlike non-magnetic SCLC, the space-charge limit does not characterize the maximum current in a CFD, which is instead determined by electron flow stability [2]. These initial studies derived solutions for the limiting current that were only valid for planar diodes [2], which are not representative of typical crossed-field devices.

This presentation assesses various approaches to derive the limiting current for non-planar diodes. We first describe the derivation of the SCLC in both magnetically insulated and non-insulated CFDs by using the Euler-Lagrange equation for planar and concentric cylinder diodes [3]. While this approach may, in principle, be extended to any general geometry, the actual mathematical application is daunting. Thus, we also apply conformal mapping, which was used to derive the mapping of the space-charge limited potential from a given geometry to the standard planar geometry, to obtain SCLC for concentric cylinders [1]. We next apply Lie point symmetries, which may be considered as a generalization of conformal mapping, to derive SCLC in other complicated geometries, including concentric spheres, which are not amenable to conformal mapping [1]. An overall assessment and comparison of the SCLC using these different techniques will be discussed, as will the extension of conformal mapping and Lie point symmetries to more complicated geometries.

[1] A. L. Garner, A. M. Darr, and N. R. Sree Harsha, “Calculating space-charge limited current density for general geometries and multiple dimensions,” IEEE Trans. Plasma Sci., submitted.
[2] P. J. Christenson, “Equilibrium, stability, and turbulence in cycloidal electron flows in crossed electric and magnetic fields,” Ph.D. dissertation, Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 1996.
[3] A. M. Darr, R. Bhattacharya, J. Browning, and A. L. Garner, “Space-charge limited current in planar and cylindrical crossed-field diodes using variational calculus,” Phys. Plasmas, vol. 28, no. 8, 2021, Art. No. 082110.

5:10pm - 5:30pm
Analytical Methods: 5

Optimization of a Set of Electron-Neutral Collision Cross Sections in Fluorinated Nitrile (C4F7N)

M. Flynn, A. Neuber, J. Stephens

Texas Tech University, United States of America

Plasma fluid models for high-voltage gaseous discharges rely on transport coefficients which are often calculated with an electron swarm kinetic model (e.g. Monte Carlo, Boltzmann equation). These calculations, however, require the input of a set of electron-neutral cross sections which are not well known for many gases. C4F7N (i.e. 3M™ Novec™ 4710) is one such gas. Owing to its short atmospheric lifespan and large dielectric strength, C4F7N has received recent attention as an insulating gas with significantly reduced global warming potential, when compared to SF6.

This report details the progress made in the development of a complete and self-consistent set of cross sections for electron swarms in C4F7N. MultiBolt, a multi-term Boltzmann equation solver, is utilized to optimize elastic and inelastic cross sections for the calculation of swarm parameters, which are compared with available literature. The cross section optimization procedure and considerations for the Boltzmann model will be discussed.

SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525


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