Efficiency Enhancement of Reflex Triode Virtual Cathode Oscillator Using the Carbon Fiber Cathode

Abstract

This paper presents the investigation on the reflex triode (RT) virtual cathode oscillator (vircator) using a carbon fiber cathode. Experimental results show that the carbon fiber cathode can obviously improve the electron beam quality and dramatically enhance the beam-to-microwave efficiency of the RT vircator. It was found that the beam-to-microwave efficiency increased from about 4%-6% in the case of the stainless steel cathode to over 10% in the case of the carbon fiber cathode. In order to understand the phenomenon of efficiency enhancement, experimental studies on the plasma formation on the surface of carbon fiber cathode were also done using the facility of the RT vircator. Physically, the electron emission of the carbon fiber cathode is attributed to the plasma formation due to the surface flashover along the whole surface of carbon fiber. This mechanism is different from the conventional explosive emission of metal cathode. Experimental results clearly show that the electrons emitted not only from the top of the carbon fiber but also from the side surface. Particularly, the plasma is more uniform for carbon fiber cathode due to the side surface flashover of the carbon fibers, and plasma expansion velocity is slower than that for conventional metal cathode, which significantly improves the electron beam quality of the carbon fiber cathode.Index Terms-Carbon fiber cathodes, electron beams, highpower microwaves (HPMs).

Shot to shot variation in perveance of the explosive emission electron beam diode

“…1 It was shown that the beam-tomicrowave efficiency can be increased by improving the electron beam quality with the use of a carbon fiber cathode. 1 It was also shown that there is a statistical correlation between emission uniformity and the shot to shot variation in diode current.…”

“…1 It was shown that the beam-tomicrowave efficiency can be increased by improving the electron beam quality with the use of a carbon fiber cathode. 1 It was also shown that there is a statistical correlation between emission uniformity and the shot to shot variation in diode current. 4 This paper reports on experimental investigation of shot to shot variation in perveance of a planar diode under nanosecond voltage pulses.…”

High power microwaves generation from intense relativistic electron beam using Kali-1000 pulse power system

“…Intense relativistic electron beams has received considerable attention during last 50 years due to its use in diverse applications such as high-power microwave generation (HPM) [1,2], free electron lasers [3], flash X-ray (FXR) generation [4], and surface modification [5]. The intense relativistic electron beam (IREB) with powers ranged in gigawatt is generated from the cold cathode by explosive electron emission process, and the electron emission occurs from the plasma which is formed on the cathode surface when the strong electric field in the order of ~10 7 V/cm is applied to the anode-cathode gap [6].…”

“…The vircator can be one of the most promising high-power microwave sources due to its conceptual simplicity, high-output power capability, and tunability. The frequency bandwidth of the vircator is known to be wide and its energy conversion efficiency is generally less than 10% [2].…”

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

“…As a low-impedance device, a vircator depends more sensitively on plasma expansion, furthermore on cathode material [8]- [13]. 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.…”