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Title: Back bombardment for dispenser and lanthanum hexaboride cathodes
Authors: Bakr, Mahmoud
Kinjo, R.
Choi, Y.
Omer, M.
Yoshida, K.
Ueda, S.
Takasaki, M.
Ishida, K.
Kimura, N.
Sonobe, T.
Kii, T.  kyouindb  KAKEN_id
Masuda, K.  kyouindb  KAKEN_id
Ohgaki, H.
Zen, H.  kyouindb  KAKEN_id  orcid (unconfirmed)
Issue Date: Jun-2011
Publisher: American Physical Society
Journal title: Physical Review Special Topics - Accelerators and Beams
Volume: 14
Issue: 6
Thesis number: 060708
Abstract: The back bombardment (BB) effect limits wide usage of thermionic rf guns. The BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during a macropulse. This paper presents a comparison of the BB effect for the case of dispenser tungsten-base (DC) and lanthanum hexaboride (LaB6) thermionic rf gun cathodes. For each, particle simulation codes are used to simulate the BB effect and electron beam dynamics in a thermionic rf gun cathode. A semiempirical equation is also used to investigate the stopping range and deposited heat power of BB electrons in the cathode material. A numerical simulation method is used to calculate the change of the cathode temperature and current density during a single macropulse. This is done by solving two differential equations for the rf gun cavity equivalent circuit and one-dimensional thermal diffusion equation. High electron emission and small beam size are required for generation of a high-brightness electron beam, and so in this work the emission properties of the cathode are taken into account. Simulations of the BB effect show that, for a pulse of 6  μs duration, the DC cathode experiences a large change in the temperature compared with LaB6, and a change in current density 6 times higher. Validation of the simulation results is performed using experimental data for beam current beyond the gun exit. The experimental data is well reproduced using the simulation method.
Rights: © 2011 American Physical Society.
DOI(Published Version): 10.1103/PhysRevSTAB.14.060708
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