10:00am - 10:20amRepetitive Pulsed Power: 1
Spark Gap with integrated triggering Laser
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 . 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 , 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.
 A. H. Guenther and J. R. Bettis, "A review of laser-triggered switching," Proc. IEEE, vol. 59, no. 4, pp. 689-697, 1971.
 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 - 10:40amRepetitive Pulsed Power: 2
COBRA DANE Radar Transmitter Group Replacement
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 - 11:00amRepetitive Pulsed Power: 3
Microscale Gas Breakdown for Microwave Fields: Theory and Simulation
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 . 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  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 , 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  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 - 11:20amRepetitive Pulsed Power: 4
Synthesis of Pulsed Forming Systems for Electromagnetic Manufacturing Process
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 - 11:40amRepetitive Pulsed Power: 5
Acoustic energy from exploding wire generated chemical reaction
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 - 12:00pmRepetitive Pulsed Power: 6
Explosive Pulsed Power: Milling operation limits of PBX 9501 and PBX 9502
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.