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

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 pHe. At U > 20 kV and pHe > 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.