Investigation of the characteristics and mechanism of subnanosecond switching of a new type of plasma switches. I. Devices with counter-propagating electron beams—kivotrons

Abstract

Novel opportunities of waveform tailoring for controlling plasma parameters based on the development of a high-voltage gas-discharge switch with a subnanosecond breakdown time and high pulse repetition frequency are discussed. The studies of characteristics and breakdown development mechanisms of the switch based on an 'open' discharge-kivotron are summarized. The discharge in the switch is carried out in conditions when counter-propagating electron beams in high electric field are generated. In this case, when using helium as an operating medium, firstly, atoms are effectively excited into the resonance state by fast particles. Secondly, due to the Doppler effect, resonant photons without reabsorption reach the cathode surface, maintaining the discharge current due to photoemission. Thirdly, fast heavy particles modify the cathode surface, thereby significantly (up to an order of magnitude) increasing the photoemission coefficient. The combination of these processes leads to an increase in the switching rate with an increase in the operating voltage U and helium pressure p He . At U > 20 kV and p He > 10 Torr, the switching time becomes less than 100 ps both in the experiment and according to the simulation. It is preferable to use planar geometry without a drift space as a switching device, in which, on the one hand, the most complete use of EB energy is realized in creating a plasma with a high charge density, on the other hand, a small wave impedance of the switch is realized. As a result, currents of tens of kiloamperes are achieved at voltages up to 100 kV. In an interpulse period plasma in the discharge gaps recombinates fast. As a result, switches can operate up to pulse repetition frequency 100 kHz. Together these achievements open new opportunities to control plasma parameters.

Operating characteristics of open discharge-based plasma switches with helium, nitrogen and oxygen

“…They are used for fast switching of high voltage pulses, generation of vacuum ultraviolet (VUV) and x-ray radiation, forming of high intensity electron beams, pumping of gas and solid-state lasers and other applications [1][2][3][4][5][6]. This class of devices also includes recently developed open discharge switching devices [7][8][9][10][11][12]. Their use makes it possible to improve the output characteristics of a number of devices and facility, in particular, copper vapor lasers [13], to generate high-frequency oscillations with a frequency of several GHz and the duration of a few pulses [8], etc.…”

“…extended drift space. A structure with two oppositely spaced discharge gaps and consequently counter propagating electron beams being generated in the discharge can function as a voltage sharper-a kivotron [7][8][9]11] with the number of commutated pulses up to at least 10 11 [6,9,14,15]. Fast switching, up to a switching time of ∼80-100 ps, is provided mainly by photoemission under the influence of resonant VUV radiation from fast helium atoms, having a large Doppler shift relative to the line center, and at the final stage of current development, due to secondary electron emission [16], which determine the long lifetime of the devices.…”

Особенности Пробоя И Развития Тока В Импульсном Открытом" Разряде

“…Тем самым ток разряда определяется в основном эмиссией электронов с катода и внешней электрической цепью. Физика разрядов подобного типа привлекает интерес благодаря их способности с высокой эффективностью генерировать электронный пучок keV-энергий с быстрым развитием тока, что позволяет на их основе создавать эффективные плазменные коммутационные устройства субнаносекундного диапазона, функционирующие при частотах следования импульсов десятки-сотни килогерц [6,7]. Данный механизм инициирования и развития тока в ОР ставит вопросы об особенностях пробоя в таких разрядах.…”

Peculiarities of breakdown and current development in a pulsed open" discharge

“…Thus, the discharge current is determined mainly by the emission of electrons from the cathode and by the external electrical circuit. The physics of discharges of this type attracts interest due to their ability to generate an electron beam of keV energies with high efficiency with a rapid current development, which allows them to be used as a basis for creating efficient subnanosecond plasma switching devices operating at pulse repetition rates of tens to hundreds of kilohertz [6,7]. This mechanism of current initiation and development in the OD raises questions about the features of breakdown in such discharges.…”

“…In this case, a glow appears in the drift space. Since at high voltage the range of electrons is by many times greater than the linear dimensions of the cell, fast electrons, accelerating in the discharge gap, then oscillate between the cathodes until complete deceleration [5,6].…”