This study presents a comprehensive investigation of electrode erosion and discharge behavior in spark gap switches over long switching cycle lifetimes. Brass, copper–tungsten (CuW), and stainless steel electrodes are tested under controlled conditions to quantify material degradation, debris accumulation, and changes in breakdown voltage. High-resolution imaging and statistical analysis of spark channel locations and gap breakdown voltages reveal how surface evolution influences long-term performance and reliability. These results provide essential data for lifetime modeling and inform design strategies for pulsed power systems in emerging applications such as private sector fusion energy and large-scale facilities like Sandia’s Z Machine and proposed ZX upgrades, where high repetition reliability and predictable behavior are critical.

Linear transformer drivers (LTDs) offer significant advantages for pulsed power applications, but solid-state implementations typically rely on MOSFETs or IGBTs that impose current handling limitations. Thyristors provide substantially higher current handling capability compared to other solid-state switches, making them highly attractive for high-current pulsed-power LTDs. However, because they cannot be turned off through gate control, conventional pulse-width modulation is not possible, limiting their use in applications that require tunable pulse durations. This paper presents a method for achieving pulse width control in thyristor-switched LTDs by exploiting controlled magnetic core saturation. By varying the magnetic reset applied to the cores prior to discharge, the available flux swing and the resulting output pulse duration can be precisely controlled. A 10-stage thyristor-switched LTD was designed and constructed to validate this approach, utilizing SP245-03 thyristors and nanocrystalline magnetic cores. The results demonstrate continuous pulse width control from 540 ns to 1.7 µs at nominal 10 kV output voltage, with the output pulse duration exhibiting a linear relationship with applied reset time up to core saturation. The measured maximum pulse width agrees well with theoretical predictions based on Faraday’s law. This work demonstrates that thyristor-based LTDs can achieve flexible pulse width modulation while benefiting from the higher current ratings these devices offer, enabling new design possibilities for high-current pulsed power systems.

This article describes the experimental characterization of small form factor gyromagnetic nonlinear transmission lines (NLTLs). These NLTLs have a highly compact coaxial geometry, with the outer conductor having an inner diameter of 3 mm. The mechanism for RF formation in these devices is gyromagnetic procession, necessitating the use of a very fast high-voltage input excitation. Three different avalanche transistor-based pulse generators are used to excite the NLTLs with negative-going pulses of either a 420 V, 280 ps, or 1000 V, 350 ps, or 1200 V, 570 ps amplitude and rise time, respectively. The performance characteristics of NLTLs of varying lengths (15, 20, or 38.1 cm) and varying axial bias field (17-44 kA/m) are presented and compared for each of the electrical input excitations. Based on the test conditions presented, RF formation in a short NLTL (15 cm) was achieved. The shorter NLTLs detailed in this work demonstrate RF production in the range of similar to 1 GHz with tuning capabilities upward of 100 MHz (>10% bandwidth) and RF output power peaking at 1.5 kW for single-shot operation. However, a reduction in tuning bandwidth (<5%) and RF output power is observed when using physically longer NLTLs. A distinct correlation is subsequently identified between the electrical specifications of the high-voltage driver and the characteristics of the compact NLTLs presented.

Pressurized gas discharge switches, commonly known as spark gaps, are fundamental to the operation of pulsed power facilities, enabling power amplification by switching enormous off-state voltages and on-state currents. Because pulsed power accelerators typically employ hundreds or even thousands of spark gaps, low-probability $(\mathrm{p}<0.001)$ failure modes significantly impact the reliability or operational limitations of such facilities. The self-breakdown voltage of a spark gap is characterized by a statistical distribution (typically Weibull or normal) attributable to the collective impact of material and interface modifications from previous discharges. Unfortunately, spark gaps are prone to anomalous self-closures at voltages well below the primary statistical distribution, which can initiate pre-fires even at substantially de-rated operating conditions. These events are difficult to study in the laboratory due to their low rates of occurrence.

Pulsed electron field emission is measured from an assortment of plastic insulators with various surface preparations. The emission is markedly stochastic in nature. Generally, there is a spatially diffuse, baseline level of emission which is observed after a few repeated pulses on a sample. In addition, localized, highly emissive sites contribute sporadically, with the estimated current for those excitations sometimes exceeding the baseline emission by orders of magnitude. Under 40-ns pulse excitation, Rexolite produces measurable currents spanning from tens of nA up to hundreds of mu A. These measurements mark a first step toward understanding initial plasma formation in anode-initiated vacuum flashover.

This study investigated RF generation in highly compact nonlinear transmission lines (NLTLs), with a 3 mm inner diameter. The general behavior of these microwave sources can be described as a damped harmonic oscillator, requiring very fast high voltage input excitations. A $\sim-400 \mathrm{V}$ avalanche transistor-based pulse generator with sub-nanosecond fall time excitation capability was used to excite the NLTLs. The experimental characterization of several NLTL lengths are presented.

Flashover is an electrical breakdown along the dielectric-gas/vacuum/liquid interface under high electric field excitation. Surface flashover phenomena in vacuum greatly impede a variety of vacuum insulation devices and systems. Here, a comprehensive perspective of the vacuum flashover global model is provided to integrate existing understandings and highlight featured prospects of the flashover mechanisms, mitigation approaches, and applications. An overview of physical processes involved in the entire vacuum flashover process is first given. Recent advances and perspectives for the understanding of these processes are then discussed separately, including the surface discharge above dielectric, and the charge transport and breakdown within dielectric bulk and surface layer. Scaling laws and empirical formulas for flashover threshold prediction are assessed as well. The mechanisms of recent vacuum flashover mitigation approaches are analyzed, such as using physical structures and geometrical modifications, material-based approaches, and applying external electromagnetic field, and possible novel flashover mitigation methods are predicted. In addition, potential applications using vacuum flashover are discussed. Finally, promising research topics, imminent challenges, and open questions of the vacuum flashover studies are presented. It might be instructive for the fundamental and application research studies of surface flashover in vacuum in future.

This work details the development of a 10-stage solid-stage linear transformer driver (SSLTD) capable of producing 24 kV, 1 kA pulses with a rise-time of ∼10 ns utilizing SiC MOSFET switches. Throughout the development process, various design parameters were investigated for their influence on the LTD’s performance. Among these considerations was an evaluation of the behavior of several nanocrystalline magnetic core materials subject to high-voltage pulsed conditions, with an emphasis on minimizing energy losses. Another design parameter of interest lies in the physical layout of the LTD structure, particularly the diameter of the central stalk and the dielectric material, which together define the characteristics of the coaxial transmission line, as well as the overall height of each stage. The influence of each of these parameters was weighed to optimize the final design for fastest output pulse rise-time, highest efficiency, and cleanest output pulse waveform profile across varying load resistance. This work also introduces a pulsed reset technique, where repetition-rated burst testing was used to find the maximum operational frequency of the LTD without driving the magnetic cores into saturation.

Electron field emission from highly stressed electrical insulators has been suggested as a possible initiating mechanism of anode-initiated flashover. A testbed designed to isolate the electron emission process from other physical effects has been fielded to investigate this behavior. Early measurements from this setup using an electron multiplier tube are reported for as-machined and graphite-contaminated Rexolite® insulator samples. With this diagnostic, emission was detectable for the contaminated samples. However, diagnostic limitations hindered measurements for the clean samples, even at large fields (>700 kV/cm) and extended pulse lengths (200 ns width), motivating the development of a higher sensitivity diagnostic.

This study reports on progress in developing high voltage pulse generators (HVPGs) for driving small printed circuit board and gyromagnetic nonlinear transmission lines (NLTLs). Two main pulse generator topologies are reported. The first is a solid-state Marx generator (SSMG), which is a new iteration on previously developed designs. This SSMG is a 5-stage device, capable of generating more than $\sim 2 \text{kV}$, with risetimes on the order of 10 ns. The second pulse generator is an inductive storage circuit topology utilizing a drift step recovery diode (DSRD) opening switch. This system has produced up to $\sim 10 \text{kV}$ with rise times on the order of a few nanoseconds. When paired with a silicon avalanche shaper (SAS), this device has produced 10 kV pulses with $\sim 1 \text{ns}$ risetime.

This work demonstrates a modeling technique focused on reproducing the behavior of magnetic cores subject to high voltage pulses. The working principle of the model is based on a magnetic circuit with additional elements that influence the model’s behavior. The elements include a function that defines the response of the model depending on the applied pulse voltage and a component that dominates the transient response. These elements are necessary to replicate the experimentally observed behavior of magnetic cores. The model was developed based on the measured behavior of three nanocrystalline magnetic materials subject to a range of pulse voltages. This modeling technique was created to address the limitations of other models in accurately capturing fast pulse responses. The key limitation of traditional modeling techniques that the proposed model addresses is their inability to capture variations in core response under different applied pulse voltages (magnetization rates). The proposed model has been shown to produce accurate results for magnetization rates between 1 T/μs and 8 T/μs, with potential for further expansion. Implemented in LTspice, this model is both fast and accurate, effectively replicating the behavior of the magnetic core while maintaining simplicity. This work outlines the foundation of this modeling technique, the trends in the parameters that influence its behavior, and its application within a simple pulsed power system. The most notable feature of this model is its ability to operate across a wide range of pulse voltages without requiring adjustments to the model parameters.

This study examines the high-voltage nanosecond pulsed breakdown performance of C4F7N compared to SF6 in volumetric breakdown and surface flashover conditions. While SF6 is extensively used in the pulsed power community, Novec 4710TM, C4F7N, is being considered as an alternative to SF6 owing to its lower estimated global warming potential. A coaxial testing apparatus enables the measurement of single digit nanosecond fast breakdown events. Volumetric breakdown testing was performed across a 2.2 mm gap using hemispherical electrodes within a pressure range of $150 \text{kPa}-450 \text{kPa}$. Mixtures of $\mathbf{2 0} \%$ and 50% C4F7N were tested with CO2 and N2 as buffer gases, and the results are compared to pure SF6 under the same conditions. Surface flashover testing involved placing a polycarbonate insert across the midplane of the spark gap electrodes.

A new test stand for spark gap switching performance testing has been developed to capture the changing surface conditions of spark gap electrodes over their lifetime. This test stand features dual-axis imaging of the discharge and the ability to image both electrode surfaces between each successive switching event by moving one of the two electrodes. The apparatus operates with adjustable gas pressure, gap distance, and electrode profile, featuring a maximum design pressure of 304 $\mathbf{k P a}$ absolute for tested gases such as synthetic air and SF6. Bipolar charging is used to apply potential differences of 80 kV across the test gap, applied via a linear voltage ramp until breakdown occurs, delivering over 1 kJ of energy per switching event with a Coulomb transfer of typically 0.1 C.

Simulated and experimental results for X-band high-power microwave (HPM) sources using split-cavity oscillators (SCO) are reported. Coaxial and rectangular SCOs are driven by a $-500 \text{kV}, \sim 10 \text{kA}$ electron beam using no guiding magnetic field in particle-in-cell (PIC) simulations and have achieved tens to hundreds of megawatts of average output microwave power at frequencies ranging from $\sim 6 \text{GHz}$ to $\sim 12$ GHz. This paper details the design, materials, and experimental results of the two tested SCO geometries.

An experimental platform supporting X-band highpower microwave (HPM) generation is reported. The platform is designed to operate with a split-cavity oscillator (SCO) HPM source, driven by a $-500 \text{kV},-10 \text{kA}$ electron beam. This work focuses on the design, construction, and implementation of the supporting systems essential for HPM generation, including the Marx generator, high-voltage feedthrough, vacuum system, and diagnostics. Over 150 shots, the platform operated without interruption and consistently delivered the required pulses, enabling successful testing of the HPM sources.

A discrete-element, printed circuit board (PCB)-based nonlinear transmission line was investigated to characterize its RF output characteristics for varying dc bias current and input pulse voltage. The device demonstrated both forward-wave and backward-wave RF formation, with each mode of operation exhibiting RF frequency and power characteristics. The forward-wave operational mode yielded a wider range of frequency tunability via variation of the applied dc bias. In contrast, the backward-wave operational mode depended more strongly on the input pulse voltage. The forward-wave operational mode generated higher instantaneous RF output power; however, the backward-wave operational mode featured longer RF pulse duration. The backward-wave mode produced consistently higher output frequency, achieving an output frequency of approximately 240 MHz for a 2.5 kV input pulse.

The breakdown behavior of insulating gases above atmospheric pressures and electric fields approaching 1 MV/cm is studied using optical emission spectroscopy. Concern surrounding the environmental impacts of Sulfur Hexafluoride (SF6) has driven significant research into using more environmentally friendly insulating gases to replace SF6 for electrical distribution and pulsed power applications. One such gas is the perfluoronitrile NovecTM 4710 (C4F7N), which is capable of twice the DC holdoff voltage of SF6 at atmospheric pressure. Optical emission spectroscopy permits observation of the performance of a subject gas during electrical breakdown, offering the ability to identify decomposition products of the gas, as well as their internal energy distribution. In this work, the optical emission spectra of NovecTM 4710, and SF6 under pulsed electrical breakdown are presented and compared at above atmospheric pressures, and an overview of the apparatus used to acquire these spectra is provided. The effects of varying gas pressure and, thus, gap voltage are explored and observed; atomic decomposition products are compared to the available literature.