科研之友
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摘要
The existence of a structural resonance stop band caused by space charge in high-current beams, where the resonance frequency is associated with 90 degrees phase advance per focusing period, is well known and alternatively referred to in the literature as envelope instability or as fourth-order resonance. We show, however, that this stop band is actually a coincidence of a structural fourth-order resonance and the much stronger envelope instability as competing mechanisms-depending on the time scale and initial matching. A similar complexity of behavior-dependent on the distribution function-is also found between a third-order instability and a sixth-order resonance in a 60 degrees stop band. We claim that these findings are a generic property of high-intensity beams in periodic focusing; they also allow a reinterpretation of the 90 degrees linear accelerator stop band previously observed experimentally at the UNILAC accelerator.
- 出版日期2015-11-10
