Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams

Abstract

This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a approximately 450 kV, approximately 400 ns pulse. It was found that 300-400 MW, approximately 250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.

Efficiency and stability enhancement of a virtual cathode oscillator

“…A virtual cathode oscillator (VCO) with the general characteristics of simple construction, without magnetic field, broadband frequency, and low impedance, is an important high-power microwave source and a major hotspot in the field of high-power microwave research at present. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] However, because of the mode competition and the frequency instability, the VCO always suffers from low efficiency and operation instability. [1,2,5,6,11] An axially-extracted VCO with a resonant cavity is an important type of VCO, and it has been investigated in detail in our laboratory.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] However, because of the mode competition and the frequency instability, the VCO always suffers from low efficiency and operation instability. [1,2,5,6,11] An axially-extracted VCO with a resonant cavity is an important type of VCO, and it has been investigated in detail in our laboratory. [11][12][13][14][15][16] In this paper, an equivalent circuit method is introduced to analyze the resonant cavity, and a theoretical expression for the fundamental mode frequency of the resonant cavity is given.…”

Characterization of Cesium Iodide-Coated Carbon-Fiber Aluminum Cathode for an <inline-formula> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula>-Band High-Efficiency Vircator

“…Previous studies demonstrate that carbon fiber is a good candidate for vircator operation owing to its low turn-ON threshold and high beam uniformity [5], [9], [13], [14]. Recently, we successfully fabricated a carbon-fiber-aluminum (CFA) cathode [15], which is robust, vacuum-compatible, long-lived, and especially suitable for repetitive operation. Characterization indicates that the plasma expansion velocity of the CFA cathode is in excess of about 6 cm/μs [16], which is high for applying to a vircator.…”

“…The CFA needles were surrounded by a stainless steel screening ring to decrease the edge effect. It was found in the experiment that the CFA cathode was capable of generating tens of kiloampere high current with high spatial uniformity [15]. To decrease plasma expansion velocity, a CsI-coating was applied on the cathode surface.…”

“…2(a), one can clearly observe that CsI particles are uniformly deposited on the surface of carbon fibers after coating. One may note that the carbon fibers become not spatially uniform as initially fabricated [15], which is mainly due to fiber rupture, erosion, and material loss after explosive electron emission for thousands of high-current pulses.…”