Multipass Beam Breakup in Recirculating Linacs
Multipass beam breakup, a transverse beam instability generated by coherent excitation of cavity higher order modes in a recirculating linac, is a particular concern in designs utilizing superconducting technology.In this paper, an analytic model is presented that includes a description of this effect for a distribution of cavities along the linac with several recirculations in an impulse approximation.For N passes and M cvities, solution of the resulting equations reduces in general to finding M zeros of a 2(N-1) dimensional determinant or equivalently the M eigenvalues of an M-dimensional matrix.The parametric dependence of this system on higher order mode frequencies and Q, lattice functions, and transit times is discussed.Numerical examples are presented to clarify these issues and to model the CEBAF superconducting linac, where threshold currents are found to exceed design currents by more than an order of magnitude.
- Research Organization:
- Thomas Jefferson Lab National Accelerator Facility
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 954098
- Report Number(s):
- CEBAF-PR-87-07
- Country of Publication:
- United States
- Language:
- English
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