Pseudospark-sourced Electron Beam for Millimeter Wave and Terahertz Radiation Generation

Abstract

The production and propagation of an electron beam from both a multi-gap and a small-scale single-gap pseudospark discharge are investigated. From a three-gap pseudospark, a beam up to 680 A was measured at the anode at an applied dc voltage of 23 kV. This beam can propagate downstream as far as 20 cm in a gaseous environment with no guiding magnetic field, which confirms that the transport of the electron beam was based on the neutralization of the space-charge of the electron beam due to the ionization of the gas molecules by the beam itself. The beam is of very small size of 1-3 mm in diameter and is ideal to drive high frequency radiation. Higher energy electron beam pulses were generated using a 14-gap pseudospark discharge powered by a cable pulser capable of producing 120 ns duration and 170 kV voltage pulses. The beam measured had a current of up to 110 A. A Ka-band Cherenkov maser and a W-band backward wave oscillator from the produced beam were simulated and experimentally studied. Millimeter wave pulses were detected successfully from both devices. In an effort to show the effects of scaling down the size of the pseudospark discharge on beam performance, a single-gap 1mm aperture pseudospark electron beam experiment was conducted, based on which a 206 GHz microklystron was designed and simulated.In recent years pseudospark discharges [1-6] have attracted significant attention from diverse fields such as pulsed-power switching, electron and ion beam generation, free electron masers, extreme-ultraviolet radiation sources and microthrusters due to their unusual and interesting discharge properties. A pseudospark is an axially symmetric, self-sustained, transient, low pressure (typically 50-500 mTorr) gas discharge in a hollow cathode / planar anode configuration which operates on the low pressure side of the hollow-cathode analogy to the Paschen curve. A potentially useful property of this type of discharge is the formation of an electron beam during the breakdown process [7,8]. During a pseudospark discharge, low temperature plasma is formed as a copious source of electrons and ions and can be regarded as a low work function surface that facilitates electron or ion extraction by applying voltages of different polarity.

Experimental Analysis of Pseudospark Sourced Electron Beam

“…Due to the absence of a hot electrode, the plasma cathode system is basically more reliable, with a longer life time, and can generate electron beams at much higher background gas pressure, even in the fore-vacuum pressure range. A characteristic feature of this type of discharge is the generation of distinctive electron beams, before and at the time of voltage collapse [7][8][9][10]. These high-power high-brightness electron beams [11] were successfully tested for applications such as thin-film deposition, plasma processing, intense pulsed charged particle sources, and X-ray sources [12].…”

“…H.Yin and colleague [7][8][9][10] had developed pseudospark plasma electron gun with a single hole channel for microwave applications. But little work has been done on the analysis of electron beam profile inside the drift space in gaseous atmosphere.…”

Numerical investigation of pseudospark discharged electron beam and propagation for W-band radiation

“…To drive a W-Band micro-klystron, the planar anode with a 0.2 mm diameter hole is utilized in the experimental setup. About a 20 mA electron beam has been obtained, which is enough to feed the W-Band micro-klystron [5][6][7][8].…”

“…A Klystron can provide high efficiency radiation and it can be scaled down in size to achieve high frequency operation in the THz band [2]. The scaled down klystron will need a high current density, high brightness electron beam to produce THz radiation [3]. A pseudospark discharge is one possible solution to provide the required very thin electron beam.…”

Design of a 0.35 THz Extended Interaction Oscillator Based on Pseudospark-Sourced Sheet Electron Beam

“…In VEDs high quality intense electron beams are required as the frequency increases. This has resulted in the pseudospark (PS) discharge attracting a lot of attention as a promising source of high quality, high intensity electron beam pulses as the beam current densities of up to 10 8 A m -2 and brightness up to 10 12 A m -2 rad -2 have been reported [3][4][5][6][7]. A PS-sourced electron beam does not require the use of an external guide magnetic field as the beam is selffocused by ion channel focusing.…”