Use of the BFCPIC and BFCRAY codes to describe space charge limited emission in electron guns for gyrotrons |
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Authors: | E Borie S Illy and T Westermann |
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Institution: | (1) Forschungszentrum Karlsruhe, ITP, Association EURATOM-FZK, P.O. Box 3640, D-76021 Karlsruhe, Germany;(2) Fachhochschule Karlsruhe, P.O. Box 2440, D-76012 Karlsruhe, Germany |
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Abstract: | Numerical modelling of an electron gun in the space charge limited regime requires determining the current density distribution
as well as the electric fields and electron trajectories. This is a rather complicated self-consistent problem, since the
space charge influences the electric field, which in turn influences the electron trajectories. Previous simulations of magnetron
electron guns using the BFCPIC and BFCRAY codes used a simple emission model (constant current density) that is approximately
valid for thermionic emission. The code has been modified to include space charge limited emission. Several different ways
of doing this are considered.
One of the models considered uses Gauss’s law to force the electric field on the emitter to vanish; it was used in the original
version of BFCPIC for the simulation of ion diodes. A second is based on the use of Child’s law (locally), which may be more
appropriate for extension to fully electromagnetic particle-in-cell (PIC) codes. Calculations were performed with both models,
and the results compared with each other and with experiments performed at FZK. |
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Keywords: | |
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