High efficiency inductive output tubes with intense annular electron beams

A Ting,R Ray,T M Antonsen,D Matthew,A Narayan,G S Nusinovich,J Appanam Karakkad,B L Beaudoin

doi:10.1063/1.4986006

Abstract

For mobile ionospheric heaters, it is necessary to develop highly efficient RF sources capable of delivering radiation in the frequency range from 3 to 10 MHz with an average power at a megawatt level. A promising source, which is capable of offering these parameters, is a grid-less version of the inductive output tube (IOT), also known as a klystrode. In this paper, studies analyzing the efficiency of grid-less IOTs are described. The basic trade-offs needed to reach high efficiency are investigated. In particular, the trade-off between the peak current and the duration of the current micro-pulse is analyzed. A particle in the cell code is used to self-consistently calculate the distribution in axial and transverse momentum and in total electron energy from the cathode to the collector. The efficiency of IOTs with collectors of various configurations is examined. It is shown that the efficiency of IOTs can be in the 90% range even without using depressed collectors.

Highlights

Heating the ionosphere with Radio Frequency (RF) waves is of interest for a variety of scientific and practical reasons
A promising source, which is capable of offering these parameters, is a grid-less version of the inductive output tube (IOT), known as a klystrode
It is shown that the efficiency of IOTs can be in the 90% range even without using depressed collectors

Summary

INTRODUCTION

Heating the ionosphere with Radio Frequency (RF) waves is of interest for a variety of scientific and practical reasons (see, e.g., Ref. 1). 103116-2 Appanam Karakkad et al. Frequency (MHz) Output power (kW) Beam voltage (kV) Beam current (A) Efficiency (%) Operating regime. Shown in the figure are the path of the beam electrons on top and the normalized momentum of the electrons (p0 1⁄4 p=mc) below, as functions of their position in the device as they pass from the cathode to the collector For this simulation, the RF voltage has been made as large as possible without reflecting any electrons. The difference between the cathode potential and the RF voltage, VSC 1⁄4 VAK À VRF;max, is due to space charge primarily in the region near the collector where the decelerated beam is slow. We can introduce Il 1⁄4 lcVA3=K2 and estimate dependence of the maximum instantaneous efficiency on current to be gI;max 1⁄4

À VSC VAK

BEAM CHARACTERIZATION

COLLECTOR DESIGN

DISCUSSION AND SUMMARY

Potential depression in a uniform pipe

Findings

Potential depression in a gap