Virtual cathode emission of an annular cold cathode

S.-D Park,J.-H Kim,J W Shin,S Y Park,J Han,M Yoon,D W Choi,J H So

doi:10.1103/physrevstab.12.113502

Abstract

Recent measurement of voltage $V$ and current $I$ of the electron gun of a relativistic klystron amplifier revealed that the resulting current-voltage relationship appeared to differ from the usual Child-Langmuir law ($I\ensuremath{\propto}{V}^{3/2}$) especially during the initial period of voltage increase. This paper attempts to explain this deviation by examining the emission mechanism using particle-in-cell simulation. The emission area in the cathode increased stepwise as the applied voltage increased and within each step the current and voltage followed the Child-Langmuir law. The electron emission began when the voltage reached a threshold, and the perveance increased with the emission area. Furthermore, an apparent virtual cathode was formed which was larger than the cathode tip. This occurs because, above a certain voltage, the emission from the edge and the side of the cathode surface dominates the emission from the front-end surface.

Highlights

A high power microwave (HPM) source is a device which generates an intense electromagnetic wave such that it can disable electronic equipment
Among many devices which have been developed as HPM sources, the relativistic klystron amplifier (RKA) generates a wave of high power, wide bandwidth, high efficiency, and stable phase and amplitude
For RKA to be used in practice, it must emit an electromagnetic wave of very high power which is sufficient to damage a circuit

Summary

INTRODUCTION

A high power microwave (HPM) source is a device which generates an intense electromagnetic wave such that it can disable electronic equipment. The SCL current estimated from the measured voltage was very close to the current measured by a beam-current monitor (BCM), but it revealed some differences, especially during the initial phase when the current increased To analyze such a behavior, we performed a particle-in-cell (PIC) simulation by dividing the cathode of 2-mm thickness into meshes of 0:1 mm, a size limited by computer capability. This simulation provided several quantities, including the voltage-dependent perveance of the cold cathode gun, the threshold voltage for emission, the rate of emission, and change in the emission area.

EXPERIMENT

MODELING AND ANALYSIS

Findings

CONCLUSIONS