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Title: An improved analytic model of electron back-bombardment in thermionic-cathode RF guns

Authors:
 [1]; ORCiD logo [2];  [1];  [1];  [1]
  1. Colorado State Unviersity, Fort Collins, CO
  2. Los Alamos National Laboratory
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
Universities/Institutions
OSTI Identifier:
1392788
Report Number(s):
LA-UR-17-28082
DOE Contract Number:
AC52-06NA25396
Resource Type:
Conference
Resource Relation:
Conference: 2015 International Particle Accelerator Conference ; 2015-05-03 - 2015-05-03 ; Richmond, Virginia, United States
Country of Publication:
United States
Language:
English
Subject:
Accelerator Design, Technology, and Operations; electron thermionic cathode back bombardment

Citation Formats

Edelen, J. P., Lewellen, John W. IV, Biedron, S. G., Harris, J. R., and Milton, S. V. An improved analytic model of electron back-bombardment in thermionic-cathode RF guns. United States: N. p., 2017. Web.
Edelen, J. P., Lewellen, John W. IV, Biedron, S. G., Harris, J. R., & Milton, S. V. An improved analytic model of electron back-bombardment in thermionic-cathode RF guns. United States.
Edelen, J. P., Lewellen, John W. IV, Biedron, S. G., Harris, J. R., and Milton, S. V. Fri . "An improved analytic model of electron back-bombardment in thermionic-cathode RF guns". United States. doi:. https://www.osti.gov/servlets/purl/1392788.
@article{osti_1392788,
title = {An improved analytic model of electron back-bombardment in thermionic-cathode RF guns},
author = {Edelen, J. P. and Lewellen, John W. IV and Biedron, S. G. and Harris, J. R. and Milton, S. V.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Sep 08 00:00:00 EDT 2017},
month = {Fri Sep 08 00:00:00 EDT 2017}
}

Conference:
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  • 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.
  • Preliminary calculations using the computer code PARMELA indicate that it is possible to achieve peak currents on the order of 1 kA using a thermionic-cathode rf gun and ballistic bunch compression. In contrast to traditional magnetic bunching schemes, ballistic bunch compression uses a series of rf cavities to modify the energy profile of the beam and properly chosen drifts to allow the bunching to occur naturally. The method, suitably modified, should also be directly applicable to photoinjector rf guns. Present work is focusing on simultaneously compressing the bunch while reducing the emittance of the electron beam. At present, the calculatedmore » normalized rms emittance is in the neighborhood of 6.8 {pi} mm mrad with a peak current of 0.88 kA, and a peak bunch charge of 0.28 nC from a thermionic-cathode gun.« less
  • DC high voltage GaAs photoguns are key components at accelerator facilities worldwide. New experiments and new accelerator facilities demand improved performance from these guns, in particular higher current operation and longer photocathode operating lifetime. This conference submission explores bulk GaAs photocathode lifetime as a function of beam current, active photocathode area, laser spot size and the vacuum of the gun and beam line. Lifetime measurements were made at 100 microamps, a beam current relevant for accelerators like CEBAF, and at beam currents of 1 milliamps and 5 milliamps, a regime that is interesting for high current Free Electron Laser (FEL)more » and Energy Recovery Linac (ERL) operation.« less
  • 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 thatmore » 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.« less
  • Energy degradation due to back-bombardment effect is quite serious to produce high-brightness electron beam with long macro-pulse with thermionic rf gun. To avoid the back-bombardment problem, a laser photo cathode is used at many FEL facilities, but usually it costs high and not easy to operate. Thus we have studied long pulse operation of the rf gun with thermionic cathode, which is inexpensive and easy to operate compared to the photocathode rf gun. In this work, to reduce the energy degradation, we controlled input rf power amplitude by controlling pulse forming network of the power modulator for klystron. We havemore » successfully increased the pulse duration up to 4 {mu}s by increasing the rf power from 7.8 MW to 8.5 MW during the macro pulse.« less