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Higher-Order-Modes and beam breakup simulations in the Jefferson Lab FEL recirculating linac

Conference ·
OSTI ID:754517
Measurements were performed of the frequencies and external Q's of the first two Higher-Order Mode (HOM) dipole passbands in the eight superconducting cavities of the cryomodule used in the recirculating linac of the driver accelerator of Jefferson Lab's IR FEL. Anomalous high-Q resonances were found, which could lead to beam instabilities at currents close to the operating current of the machine. These results led to more detailed simulations of its beam breakup (BBU) behavior. The analysis indicates that a few modes are responsible for the relatively low value of 27 mA of the threshold current. A simple modification of the superconducting cavities could lead to an increase of the threshold current by an order of magnitude.
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:
754517
Report Number(s):
DOE/ER/40150-1355; JLAB-ACC-98-09
Country of Publication:
United States
Language:
English