Electron beam generation in a diode with a gaseous plasma electron source I: Plasma source based on a hollow anode ignited by a multi-arc system

Abstract

We report on the operation of an electron diode with a cathode based on a hollow plasma anode (HPA) design. Six arc sources placed inside the anode cavity were used to produce a preliminary plasma. The latter was used to produce a high-current (up to 4 kA) gaseous discharge without formation of plasma spots at the anode wall and output grid. The plasma parameters inside the HPA were measured for different N2 and Xe gas pressures and discharge current amplitudes. It was found that the HPA operation is characterized by a negative anode potential fall and that the plasma density and temperature inside the anode are ≈6×1012 cm−3 and ≈9 eV, respectively. The characteristics of an electron diode and the generated electron beam were studied under an accelerating voltage amplitude ⩽250 kV and 400 ns pulse duration for different parameters of the HPA. It was found that in the beginning of the accelerating pulse the diode operates in a plasma prefilled mode while later the diode current is determined by the emission capability of the HPA plasma. It was shown that this source allows generation of an electron beam with a cross-sectional area of 100 cm2 and a current amplitude up to 1.2 kA, without the formation of explosive plasma at the surface of the HPA output grid.

Drastic changes in the plasma potential inside a hollow anode during an applied accelerating pulse

“…We used an experimental setup similar to that described in refs. [3] and [4]. However, in the present case the HA was grounded and the collector was at high-voltage (HV) positive potential (see fig.…”

“…One of the main advantages of the hollow-anode (HA) plasma source is that one can control the parameters of the plasma by changing the amplitude of the discharge current I d or the pressure inside the HA [1,2]. Our experiments with the HA [3][4][5] showed that the use of either an arc or a magnetron-like plasma source or a ferroelectric plasma source (FPS) allows one to achieve reliable ignition and sustainment of the discharge with amplitude of I d ≤ 4 kA and pulse duration of ∼ 2 × 10 −5 s at background pressure of P ∼ = 2 × 10 −2 Pa and without formation of plasma spots at the HA walls and at the HA output grid. It was found that the plasma acquires a positive potential of ≤ 40 V with respect to the HA and that the plasma density and electron temperature are n ≤ 10 13 cm −3 and T e ≤ 10 eV, respectively.…”

“…Also, it was shown that the incorporated FPS serves as a powerful electron source and that it allows one to decrease significantly the overall dimensions of the HA [5]. These HAs were used as cathodes in a diode for the generation of 100 cm 2 cross-sectional area electron beams with amplitude of I b ≤ 2 kA under an accelerating pulse of ϕ ac ≤ 400 kV and pulse duration of τ p ≤ 400 ns without formation of explosive plasma at the HA grid [3][4][5].…”

Non-disturbing measurements of hollow-anode plasma parameters

“…It was shown that continuous (of several microseconds) operation of the HA becomes possible owing to the formation of a dense plasma on the surface of the ferroelectric samples. This plasma formation can be considered a self-consistent process because of the absence of additional power supplies which are commonly used in cases of thermionic [5], multiple-arc and magnetron [4,6] electron sources. At present we do not know the exact mechanism of the continuous plasma formation.…”

“…This FPS-assisted HA plasma source served as a cathode in a diode generating electron beams with current amplitudes up to I b ≈ 1.5 kA and electron energies up to 300 keV [3]. It was shown that the FPS-assisted HA plasma source is the most efficient pulsed electron source among other investigated plasma sources owing to the high efficiency of electron beam extraction (I d ≈ I b ), the simplicity of the HA discharge ignition and its sustenance without the requirement of additional powerful sources of current and voltage [4][5][6]. It was found that the parameters of the generated electron beam (current amplitude and cross-sectional current density uniformity) depend on the parameters of the plasma produced by the HA.…”