Abstract
A new two-dimensional beam-tracking simulation code for electron injectors using a bulk-to-point calculation technique for space charge fields was developed. The calculated space charge fields are produced not by a point charge but by a hollow cylinder that has a volume. Each tracked electron is a point charge. This bulk-to-point calculation technique for space charge fields is based on that used in the multiple beam envelope equations, which were developed by the author. The multiple beam envelope equations are a set of differential equations for investigating the beam dynamics of electron injectors and can be used to calculate bunched beam dynamics with high accuracy. However, there is one limitation. The bunched beam is assumed to be an ensemble of several segmentation pieces in both the transverse and longitudinal directions. In this bunch model, each longitudinal segmentation slice in a bunch must not warp; consequently, the accuracy of the calculated emittance is reduced in the case of a highly charged beam for calculations of a typical rf gun injector system. This limitation is related to the calculation model of longitudinal space charge fields. In the newly developed beam-tracking simulation code, the space charge field calculation scheme is upgraded and the limitation has been overcome. Therefore, the applicable range is extended while maintaining the high accuracy of emittance calculations. Simultaneously, the calculation time is markedly shortened because the emittance dependence on the segmentation number is extremely weak. In this paper, several examples of beam dynamics that cannot be calculated accurately using the multiple beam envelope equations are demonstrated using the new beam-tracking simulation code. The accuracy of the calculated emittance is also discussed.
Highlights
The emittance calculation technique is important in the design of electron injectors, very low emittance electron sources such as X-ray free-electron lasers
The calculated emittances often depend on the number of particles. These dependences are often caused by the calculation scheme of the space charge field which is produced by a point charge
For accurate emittance calculations of short bunched electron beam dynamics, the author developed a semianalytical solution [13,14], which was proposed in 2012, by combining an analytical method and a simulation method using a set of beam envelope equations with the calculation technique for the space charge field produced by a bulk charge
Summary
JASRI/SPring-8, 1-1-1 Koto, Sayo, Hyogo 679-5198, Japan (Received 11 December 2015; published 29 February 2016). A new two-dimensional beam-tracking simulation code for electron injectors using a bulk-to-point calculation technique for space charge fields was developed. Each tracked electron is a point charge This bulk-to-point calculation technique for space charge fields is based on that used in the multiple beam envelope equations, which were developed by the author. Each longitudinal segmentation slice in a bunch must not warp; the accuracy of the calculated emittance is reduced in the case of a highly charged beam for calculations of a typical rf gun injector system This limitation is related to the calculation model of longitudinal space charge fields.
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