Four different configurations of plasma cathode electron (PCE) guns have been designed and developed in which pseudospark discharge concept has been used. Experimental studies have been performed to identify the dependence of geometrical design parameters like shape of aperture, distribution of apertures, and the number of gaps between hollow cathode and anode on high-energy and high-current-density electron beam emissions. The beam current density has been increased around five times by changing the shape of aperture from circular to sheet keeping the aperture area and other geometrical parameters identical. The perveance of the electron beam has also been increased by increasing the number of apertures on hollow cathode and anode surface. The beam current density from single aperture to multiple apertures has increased from 225 to 900 A/cm ² with low beam energy for the multiple-aperture case. The multiple gaps between hollow cathode and anode increase the electron beam energy. The maximum beam energy is found to be 16-14.5 keV at an applied gap voltage of 16 kV from the developed multigap PCE gun, which is much higher than that from the single gap configuration.

In this article, a trigger unit has been implemented to generate a high-current-density electron beam from a pseudospark (PS) discharge-based electron gun. A trigger pulse power supply unit has been designed and developed to provide the seed electrons from the ferroelectric cathode (FEC). The FEC has been used inside the hollow cathode cavity of a single-gap PS discharge-based electron gun. The electron gun has been operated in the self-breakdown as well as the trigger-based breakdown mode. A comparative analysis has also been performed between self-breakdown and trigger breakdown modes with the developed trigger unit's help for different applied gap voltages ranging between 0 and 16 kV. The designed trigger unit is based on a high-voltage-gain isolated dc-dc converter and a pulse-forming network. It is compact and capable of generating a negative pulse of ~-5 kV with a pulsewidth of ~500 ns. It provides better control over PS discharge to produce a high-current-density electron beam.

A nanosecond pulse generator (NSPG), with a high peak voltage, short-duration pulsewidth, high repetition rate, and fast rise/fall times, has gained traction and is now used in several applications such as plasma, biomedical, and industrial. The pulse characteristics vary with the type of application and these are affected by the choice of the switching devices in any topology and other elements of NSPG. Therefore, a variety of NSPGs have been researched, which makes the selection of any particular topology for NSPG development a challenging task. Thus, to address this gap, the literature presents a review of several conventional and state-of-the-art topologies of NSPG with high-power (HP) switching devices such as spark gap, solid-state switches, magnetic switches, and other elements for various applications. It also presents the pulse’s duration, voltage, current, power, rise/fall time, and repetition frequency for different applications. Furthermore, strategies for minimizing switching losses and other losses that substantially lower pulse generator efficiency are also discussed. Finally, a concise evaluation of available switching devices and other elements of NSPG, their pros and cons, and future directions are discussed to provide a clear understanding to designers and researchers.

For high-power and compact sub-terahertz (THz) sources, a high-current electron beam is a crucial component. In this article, a miniaturized sheet-electron-beam source has been developed for generation of the high-current-density electron beam. It consists of a hollow cathode with a 3-mm diameter circular aperture, an anode with a 1.25 mm $\times0.25$ mm rectangular aperture, and an interelectrode three-gap region with optimized dimension. The developed electron beam source has been operated in self-breakdown conditions for applied gap voltage ranging between 10 and 30 kV. The sheet electron beam has been successfully propagated for nearly 45 mm inside the drift space without the assistance of an external magnetic field due to the space charge neutralization effect. It has demonstrated good transmission characteristics with more than 50-A beam current and beam current loss of around 25%.

In this article, a comparative experimental and simulations analysis has been carried out to understand the role of tapered gap region on current density and energy of pseudospark (PS)-based electron beam emission. These studies have been performed for 5-gap and 8-gap regions in a tapered multigap multiaperture-based PS electron beam source, keeping the same electron beam fill factor, and other geometrical parameters identical. The source has been operated in a self-breakdown mode. Around four-times increase in the beam current has been observed in the 8-gap case at the fixed applied gap potential ranging between 20 and 25 kV, whereas the tapered interelectrode gap angle has been reduced from 7.5° to 4.5°. The field penetration inside the hollow cathode cavity and tapered region have also been analyzed using simulations, and the obtained results are explained based on built-up space charge in these regions.

In this article, the design approach for a V-band miniaturized oscillator with a pseudospark-based high-current-density sheet electron beam source is presented. The hollow cathode electron gun has been designed and developed. In the experiment, the ~10-A current in the hollow-cathode phase has been measured. The high-frequency structure comprised of a truncated sine waveguide slow wave structure (TSW SWS) with wideband-matched output couplers has been designed, optimized, and simulated. The simulations show good transmission characteristics of the structure. The operation of a backward-wave oscillator with the designed TSW SWS driven by a 10-A, 40-kV sheet electron beam has been investigated by using 3-D particle-in-cell simulations. The maximal output power of 70 kW has been attained in the simulation. Frequency tuning within the 10-GHz frequency band has been demonstrated.