Effect of cathode and anode materials on the high-energy electron beam in the nanosecond-pulse breakdown in gas-filled diodes

Abstract

High-energy electron beam can be generated during the breakdown process in a gas diode at elevated pressures. The design of electrodes in the gas diode affects the parameters of these electron beams. In this paper, investigation on parameters of the runaway electron beam (REB) in air and nitrogen excited by nanosecond pulsed generators are presented. Experiments were carried out with gas diodes by using cathode and anode made of different materials, including stainless steel, aluminum, copper and titanium. Experimental results show that, in the case of nanosecond-pulse breakdown, the cathode material significantly affects the amplitude of the REB current pulse when either pressure or gap spacing are small. When the pressure is low, the REB current is highest for the stainless steel cathode due to its small electron work function. However, the REB current for the aluminum, copper and titanium cathodes is higher than that of stainless steel cathode at atmospheric pressure because of the Malter effect on their surfaces. The dependence of the amplitude of the REB current on the anode foils is investigated by using aluminum, titanium, copper and tantalum. The experimental results show that the atomic number of the metal, as well as mass mean free path of the electron in it contribute to the amplitude of the REB current pulse. Based on the REB currents of different anode foils, energy distribution of runaway electrons is estimated. Electron distribution with an average energy of ~55 keV is obtained when the amplitude of the applied voltage pulse across the discharge gap is 110 kV. The results may contribute to the design of the gas diode for the generation of high-energy electron beams in nanosecond-pulse breakdown.

Mode transition and plasma characteristics of nanosecond pulse gas–liquid discharge: Effect of grounding configuration

“…Some common methods have been presented to prevent the instability and the transition from streamer to spark modes. Being recognized as fast‐rising but short duration, high voltage pulse power is an effective candidate to restrict the discharge mode transition . The fast‐rising time results in a high rate of variation of voltage ( dV / dt ) in the gas gap, and free electrons are greatly accelerated, leading to the fast ionization and uniform discharge .…”

“…The fast‐rising time results in a high rate of variation of voltage ( dV / dt ) in the gas gap, and free electrons are greatly accelerated, leading to the fast ionization and uniform discharge . Meanwhile, the energy of the pulse power is consumed for generating active species, instead of heating gas, and thermal instability of the gas–liquid discharge can be avoided . Furthermore, the short duration time is also beneficial for discharge stability because the plasma can extinguish before the instability occurs …”

“…Being recognized as fast-rising but short duration, high voltage pulse power is an effective candidate to restrict the discharge mode transition. [10,11] The fast-rising time results in a high rate of variation of voltage (dV/dt) in the gas gap, and free electrons are greatly accelerated, leading to the fast ionization and uniform discharge. [12] Meanwhile, the energy of the pulse power is consumed for generating active species, instead of heating gas, and thermal instability of the gas-liquid discharge can be avoided.…”

“…[12] Meanwhile, the energy of the pulse power is consumed for generating active species, instead of heating gas, and thermal instability of the gas-liquid discharge can be avoided. [10,11] Furthermore, the short duration time is also beneficial for discharge stability because the plasma can extinguish before the instability occurs. [13] Inserting a dielectric in the discharge circuit may be another possible way to restrict the discharge instability.…”

Fabrication of iron carbide by plasma-enhanced atomic layer deposition

“…Hydrogen plasma was used as a co-reactant. It is well known that the use of plasma in PEALD results in a significant decrease in the deposition temperature due to the high reactivity of the active species generated in plasma [31,32,33]. In this case, highquality iron carbide film can be produced at a low temperature down to 90°C.…”