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Title: Inverse Marx modulators for self-biasing klystron depressed collectors

Abstract

A novel pulsed depressed collector biasing scheme is proposed. This topology feeds forward energy recovered during one RF pulse for use on the following RF pulse. The presented ''inverse'' Marx charges biasing capacitors in series, and discharges them in parallel. Simulations are shown along with experimental demonstration on a 62kW klystron.

Authors:
 [1]
  1. SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
US DOE Office of Science (DOE SC), Basic Energy Sciences (BES), High Energy Physics (HEP)
OSTI Identifier:
1149329
Report Number(s):
SLAC-PUB-16052
Journal ID: ISSN 0013-5194
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Electronics Letters; Journal Volume: 50; Journal Issue: 18
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; ENG

Citation Formats

Kemp, Mark A. Inverse Marx modulators for self-biasing klystron depressed collectors. United States: N. p., 2014. Web. doi:10.1049/el.2014.1237.
Kemp, Mark A. Inverse Marx modulators for self-biasing klystron depressed collectors. United States. doi:10.1049/el.2014.1237.
Kemp, Mark A. Thu . "Inverse Marx modulators for self-biasing klystron depressed collectors". United States. doi:10.1049/el.2014.1237. https://www.osti.gov/servlets/purl/1149329.
@article{osti_1149329,
title = {Inverse Marx modulators for self-biasing klystron depressed collectors},
author = {Kemp, Mark A.},
abstractNote = {A novel pulsed depressed collector biasing scheme is proposed. This topology feeds forward energy recovered during one RF pulse for use on the following RF pulse. The presented ''inverse'' Marx charges biasing capacitors in series, and discharges them in parallel. Simulations are shown along with experimental demonstration on a 62kW klystron.},
doi = {10.1049/el.2014.1237},
journal = {Electronics Letters},
number = 18,
volume = 50,
place = {United States},
year = {Thu Jul 31 00:00:00 EDT 2014},
month = {Thu Jul 31 00:00:00 EDT 2014}
}
  • Depressed collectors have been utilized successfully for many years to improve the electrical efficiency of vacuum electron devices. Increasingly, pulsed, high-peak power accelerator applications are placing a premium on electrical efficiency. As RF systems are responsible for a large percentage of the overall energy usage at accelerator laboratories, methods to improve upon the state-of-the-art in pulsed high-power sources are desired. This paper presents a technique for self-biasing the stages in a multistage depressed collector. With this technique, the energy lost during the rise and fall times of the pulse can be recovered, separate power supplies are not needed, and existingmore » modulators can be retrofitted. Calculations show that significant cost savings can be realized with the implementation of this device in high-power systems. In this paper, the technique is described along with experimental demonstration. (auth)« less
  • A three-dimensional (3-D) package for simulation of asymmetric and crossed-field multistage depressed collectors for microwave tubes has been developed. This package is based upon the 3-D finite-difference code KOBRA3-INP. The main features of the package are a user-friendly input interface, post-processors for collector analysis and calculation of secondary electron trajectories, and versatile output graphics. Both PC and mainframe versions of the package have been developed. The results of simple benchmark tests and those of simulation and analysis of asymmetric and crossed-field collectors including the effects of secondary electrons are presented. It is found that the asymmetric hyperbolic electric field collectormore » shows very low backstreaming. It is shown that the representation of trajectories in energy space gives a better insight into the behavior of individual trajectories than plotting in coordinate space. The package will be useful for designing novel types of depressed collector.« less
  • Two 140 GHz gyrotrons with a single-step depressed collector have been operated. The different position of the isolating collector gap in the stray magnetic field causes the electron motion in the retarding region to be in one case adiabatic and in the other case nonadiabatic. The kind of motion within the retarding field influences strongly the behavior of the gyrotron with a depressed collector. In the case of nonadiabatic motion a significant amount of transverse momentum is given to the electrons reflected at the collector potential. This causes the reflected electrons to be trapped between the magnetic mirror and themore » collector. The electrons escape from the trap by diffusion across the magnetic field to the body of the tube thus contributing to the body current. Despite the high body current there is no observable influence of the collector voltage on the RF output power. In the case of adiabatic motion the reflected electrons do not gain a sufficient amount of transverse momentum to be trapped by the magnetic mirror. They pass the cavity toward the gun and they are trapped between the negative gun potential and the collector. The interaction with the RF field by electrons traveling through the cavity enhances the diffusion in the velocity space thus enabling the trapped electrons to overcome the potential barrier and escape toward the collector. Therefore the body current stays at low values since in this case the reflected electrons do not contribute to it. However, at higher collector voltages a reduction of RF power occurred and some noise in the electron beam was observed. The main motivation for the development of gyrotrons in the frequency range above 100 GHz with power levels in excess of several hundreds kW per tube, is the application in magnetic fusion devices for plasma heating and for electron current drive.« less
  • An e-gun, depressed collector, and guide-field solenoid have been designed and tested for operation at a maximum of 400 kV and 38 A in order to simulate key components of a typical low-voltage free electron laser (FEL). Detailed beam-energy-spread analyses and computer simulations are presented for the e-gun and the drift regions. The results of experiments with the depressed collector show beamcurrent-recovery efficiencies of over 90 percent for e-beam voltages from 160 to 400 keV. The authors have also set up and confirmed computercode predictions that a space-charge depression in the collector (which is essential for efficient collection) forms atmore » a collector-voltage setting of 1 percent of the beam voltage. These results demonstrate the validity of substantially increasing the efficiency of systems by using depressed collectors to recover the bulk of the energy which is left in the e-beam after it leaves the laser resonator. The recovery-efficiency parameter (recovered current/cathode-emission current) is shown to be a function of the relativistic-orbit parameter (B/..beta gamma..) and reaches a maximum of 94 percent. These results imply that FEL system efficiencies can be achieved which are an order of magnitude higher per stage than would be possible without the use of depressed collection.« less
  • An analytic and numerical study of the feasibility of depressed collectors for gyrotrons for accelerator applications was performed and a specific design for a 10-GHz 30-MW gyroklystron was realized. The conclusion of the study is that depressed collectors are feasible for gyrotrons of interest for accelerator applications (i.e., P [<=] 100 MW, 10 GHz < [line integral] < 35 GHz), and that their use would reduce capital costs for the RF system for a typical large accelerator by roughly 40%. In addition, scaling studies indicate that depressed collector are feasible for fusion-related gyrotron oscillators, such as the 1-MW, 280-GHz devicesmore » being developed for use on the Compact Ignition Tokamak (CIT).« less