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Critical Choice: Structure BPMs. PT 25-Aug-2005. Pros/Cons. Measuring the HOMs from the cavities, and feeding that information to the control room, is almost all “pro” Doesn’t have any negative impact on beam dynamics, system length… HOMs already there “for free”
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Critical Choice: Structure BPMs PT 25-Aug-2005
Pros/Cons • Measuring the HOMs from the cavities, and feeding that information to the control room, is almost all “pro” • Doesn’t have any negative impact on beam dynamics, system length… • HOMs already there “for free” • Only arguments against are cost • Digitizing hardware, controls software, etc. • Simulation studies to date have not assumed instrumented HOMs • Mostly seem to be okay
Conclusions and Caveats • PRELIMINARY indications: not needed for achieving the desired emittance • Could potentially benefit the tuning: • In the bunch compressor • In the low energy end of the linac • Can’t yet quantify this benefit • We would be especially interested in measuring the angle between the cavity’s fundamental mode and the beam axis • Assumed TESLA-like main linac • Could find that we need instrumented HOMs • If TDR cavity and module installation tolerances can’t be met • If lattice focusing is significantly relaxed • If LL or RE cavities are assumed instead of TESLA-style • Any cryomodule equipped with HOM BPMs should also be equipped with remote-controlled mover