Suppression of Multipass, Multibunch Beam Breakup in Two Pass Recirculating Accelerators
Beam Breakup (BBU) occurs in all accelerators at sufficiently high currents. In recirculating accelerators, such as the energy recovery linacs used for high power FELs, the maximum current has historically been limited by multipass, multibunch BBU, a form that occurs when the electron beam interacts with the higher-order modes (HOMs) of an accelerating cavity on one pass and then again on the second pass. This effect is of particular concern in the designs of modern high average current energy recovery accelerators utilizing superconducting technology. In such two pass machines rotation of the betatron planes by 90a, first proposed by Smith and Rand in 1980 [1], should significantly increase the threshold current of the multibunch BBU. Using a newly developed two-dimensional tracking code, we study the effect of optical suppression techniques on the threshold current of the JLAB FEL Upgrade. We examine several optical rotator schemes and evaluate their performance in terms of the instability threshold current increase.
- Research Organization:
- Thomas Jefferson National Accelerator Facility, Newport News, VA (US)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 828677
- Report Number(s):
- JLAB-ACP-04-270; DOE/ER/40150-2864
- Country of Publication:
- United States
- Language:
- English
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