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Title: Current transmission and nonlinear effects in un-gated thermionic cathode RF guns

Abstract

Un-gated thermionic cathode RF guns are well known as a robust source of electrons for many accelerator applications. These sources are in principle scalable to high currents without degradation of the transverse emittance due to control grids but they are also known for being limited by back-bombardment. While back-bombardment presents a significant limitation, there is still a lack of general understanding on how emission over the whole RF period will affect the nature of the beams produced from these guns. In order to improve our understanding of how these guns can be used in general we develop analytical models that predict the transmission efficiency as a function of the design parameters, study how bunch compression and emission enhancement caused by Schottky barrier lowering affect the output current profile in the gun, and study the onset of space-charge limited effects and the resultant virtual cathode formation leading to a modulation in the output current distribution.

Authors:
 [1];  [2]
  1. Fermilab
  2. Air Force Weapons Lab
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1358102
Report Number(s):
arXiv:1705.01386; FERMILAB-PUB-17-083-AD
1598071
DOE Contract Number:
AC02-07CH11359
Resource Type:
Journal Article
Resource Relation:
Journal Name: TBD
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS

Citation Formats

Edelen, J. P., and Harris, J. R. Current transmission and nonlinear effects in un-gated thermionic cathode RF guns. United States: N. p., 2017. Web.
Edelen, J. P., & Harris, J. R. Current transmission and nonlinear effects in un-gated thermionic cathode RF guns. United States.
Edelen, J. P., and Harris, J. R. 2017. "Current transmission and nonlinear effects in un-gated thermionic cathode RF guns". United States. doi:. https://www.osti.gov/servlets/purl/1358102.
@article{osti_1358102,
title = {Current transmission and nonlinear effects in un-gated thermionic cathode RF guns},
author = {Edelen, J. P. and Harris, J. R.},
abstractNote = {Un-gated thermionic cathode RF guns are well known as a robust source of electrons for many accelerator applications. These sources are in principle scalable to high currents without degradation of the transverse emittance due to control grids but they are also known for being limited by back-bombardment. While back-bombardment presents a significant limitation, there is still a lack of general understanding on how emission over the whole RF period will affect the nature of the beams produced from these guns. In order to improve our understanding of how these guns can be used in general we develop analytical models that predict the transmission efficiency as a function of the design parameters, study how bunch compression and emission enhancement caused by Schottky barrier lowering affect the output current profile in the gun, and study the onset of space-charge limited effects and the resultant virtual cathode formation leading to a modulation in the output current distribution.},
doi = {},
journal = {TBD},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 5
}
  • In this paper we derive analytical expressions for the output current of an un-gated thermionic cathode RF gun in the presence of back-bombardment heating. We provide a brief overview of back-bombardment theory and discuss comparisons between the analytical back-bombardment predictions and simulation models. We then derive an expression for the output current as a function of the RF repetition rate and discuss relationships between back-bombardment, fieldenhancement, and output current. We discuss in detail the relevant approximations and then provide predictions about how the output current should vary as a function of repetition rate for some given system configurations.
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