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Power Overhead Reduction Considerations for RF Field Control in Beam Commissioning

Document #:
Document type:
Tech Note
Submitted by:
Rihua Zeng
Updated by:
Rihua Zeng
Document Created:
14 Mar 2013, 07:30
Contents Revised:
14 Mar 2013, 07:30
Metadata Revised:
14 Mar 2013, 07:30
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The perturbations to cavity field in ESS high beta cavities caused by different beam loading as well as corresponding power overhead consumption under feedback are analyzed for (a) beam modes with same peak current, (b) beam modes with the same pulse length, (c) beam modes with very short pulse length for RF phase and amplitude setting. The maximum peak power consumed under feedback goes up as beam peak current increases, but keeps the same if only the pulse length changes (pulse length >10μs). For the even shorter pulse (<1μs), the perturbation to cavity field is not significant and so does the power overhead consumption.
Two methods to reduce power overhead consumption are discussed (a) using a perfect limiter, (b) using individual feedforward compensation for each beam mode. The former needs more investigation with klystron linearization, while the latter seems promising along with adaptive feedforward.
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