Design and Simulation of a Multi-Sheet Beam Terahertz Radiation Source Based on Carbon-Nanotube Cold Cathode.

Yifan Zu,Hailong Li,Matthew T Cole,Yong Yin,Xiaotao Xu,Bin Wang,Yang Yan,Yu Zhang,Xuesong Yuan

doi:10.3390/nano9121768

Abstract

Carbon nanotube (CNT) cold cathodes are proving to be compelling candidates for miniaturized terahertz (THz) vacuum electronic devices (VEDs) owning to their superior field-emission (FE) characteristics. Here, we report on the development of a multi-sheet beam CNT cold cathode electron optical system with concurrently high beam current and high current density. The microscopic FE characteristics of the CNT film emitter is captured through the development of an empirically derived macroscopic simulation model which is used to provide representative emission performance. Through parametrically optimized macroscale simulations, a five-sheet-beam triode electron gun has been designed, and has been shown to emit up to 95 mA at 3.2 kV. Through careful engineering of the electron gun geometric parameters, a low-voltage compact THz radiation source operating in high-order mode is investigated to improve output power and suppress mode competition. Particle in cell (PIC) simulations show the average output power is 33 W at 0.1 THz, and the beam–wave interaction efficiency is approximately 10%.

Highlights

Due to its wide bandwidth, good directionality, high spatial and temporal resolution, terahertz (THz) technology has attracted wide interest in a range of applications, such as high data rate communications, radar systems, electronic countermeasures, biomedical diagnostics, and security inspection [1,2,3,4,5,6]
The gap between the emitter and the HF system will be dramatically shortened in a cold cathode electron optical system, thereby relaxing design difficulties associated with the need for precise alignment of the beam
In the study of the Carbon nanotube (CNT) film emitters, prepared by Yan et al [32], we found that the chemical vapor deposition (CVD)-deposited CNTs greatly improved the emission current density compared to slurry based methods, which we attribute to the enhanced adhesion between the CNTs and the substrate

Summary

Introduction

Due to its wide bandwidth, good directionality, high spatial and temporal resolution, terahertz (THz) technology has attracted wide interest in a range of applications, such as high data rate communications, radar systems, electronic countermeasures, biomedical diagnostics, and security inspection [1,2,3,4,5,6]. As the device gets smaller, a smaller electron beam with high current is used to keep the beam diameter sufficiently smaller than the device operating wavelength This is becoming increasingly difficult to engineer, as almost all commercially available modern THz VEDs employ thermionic cathode electron guns. Due to their high operating temperature, thermionic cathodes must be kept at comparatively long working distances and be placed sufficiently distant from the HF system so as to not induce thermal damage. As a result, it has proven especially challenging for the electron beam to enter the HF system, which is necessary to achieve efficient beam–wave interaction required for THz generation. The gap between the emitter and the HF system will be dramatically shortened in a cold cathode electron optical system, thereby relaxing design difficulties associated with the need for precise alignment of the beam

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Conclusion