Coupler Design for the LCLS Injector S-Band Structures

The LCLS injector is required to provide a 1-nC, 10-ps bunch with a normalized rms transverse projected emittance of less than 1 micron. The LCLS beam is generated and accelerated in a 1.6-cell S-band RF gun at 120 MV/m up to 6 MeV. The gun is followed by two SLAC 3-m S-band accelerator structures t...

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Bibliographic Details
Main Authors: Zenghai Li, Jose Chan, Bentson, L.D., Dowell, D.H., Limborg-Deprey, C., Schmerge, J.F., Schultz, D.
Format: Conference Proceeding
Language:English
Subjects:
Acceleration
Contracts
Feeds
Finite element methods
Linear particle accelerator
Optical coupling
Particle beams
Radio frequency
Scattering parameters
US Department of Energy
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Summary:The LCLS injector is required to provide a 1-nC, 10-ps bunch with a normalized rms transverse projected emittance of less than 1 micron. The LCLS beam is generated and accelerated in a 1.6-cell S-band RF gun at 120 MV/m up to 6 MeV. The gun is followed by two SLAC 3-m S-band accelerator structures to further accelerate the beam to 135 MeV which moves the beam out of the space-charge dominated regime. In the SLAC S-band structures, the RF power feed is through a single coupling-hole (single-feed coupler) which results in a field asymmetry. The time dependent multipole fields in the coupler induce a transverse kick along the bunch and cause the emittance to increase above the LCLS specification. To meet the stringent emittance requirements for the injector, the single-feed couplers will be replaced by a dual-feed racetrack design to minimize the multipole field effects. We will present detailed studies of the multipole fields in the SLAC linac RF coupler and the improvements with the dual-feed ractrack design using the parallel finite element S-parameter solver S3P.
ISSN:1944-4680
2152-9582
DOI:10.1109/PAC.2005.1591048