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Research output: Thesis › Doctoral Thesis
Research output: Thesis › Doctoral Thesis
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TY - BOOK
T1 - Higher Order Modes and Dampers for the LHC Double Quarter Wave Crab Cavity
AU - Mitchell, James
PY - 2019/10/10
Y1 - 2019/10/10
N2 - This thesis initially investigates the DQW crab cavity HOM couplersmanufactured for tests in the Super Proton Synchrotron (SPS) atCERN and proposed for the HL-LHC upgrade. The coupler’s aremodelled using equivalent circuit analysis and ‘test-boxes’ are usedto measured each of the six HOM couplers for the SPS test.The DQW crab cavity’s impedance spectra and resulting HOM powergeneration as a result of excitation by the high-current HL-LHC beamis quantified. Following this, HOM measurements are used to characterise the deviations from the simulated case. Evaluation of theDQW’s impedance spectra and stochastic analysis of the foreseeableHOM power generation in the HL-LHC highlights potential issues withthe HOMs. To mitigate the issues, a re-design of the HOM coupler ispresented; The impedance and HOM power are quantified and benchmarked. In parallel, a new ‘quarter wave’ rejection filter is designedand evaluated. The operation of the HOM couplers in the presenceof the operating electromagnetic field is assessed, quantifying thermaland multipacting behaviour.Finally, first measurements of crab cavity HOMs with proton bunchesare presented and compared with simulations. The measurementsare used to evaluate the accuracy of the methods used to calculateimpedance and HOM power. Several conclusions feed-back into ancillary design and acceptance criteria for future manufacture.
AB - This thesis initially investigates the DQW crab cavity HOM couplersmanufactured for tests in the Super Proton Synchrotron (SPS) atCERN and proposed for the HL-LHC upgrade. The coupler’s aremodelled using equivalent circuit analysis and ‘test-boxes’ are usedto measured each of the six HOM couplers for the SPS test.The DQW crab cavity’s impedance spectra and resulting HOM powergeneration as a result of excitation by the high-current HL-LHC beamis quantified. Following this, HOM measurements are used to characterise the deviations from the simulated case. Evaluation of theDQW’s impedance spectra and stochastic analysis of the foreseeableHOM power generation in the HL-LHC highlights potential issues withthe HOMs. To mitigate the issues, a re-design of the HOM coupler ispresented; The impedance and HOM power are quantified and benchmarked. In parallel, a new ‘quarter wave’ rejection filter is designedand evaluated. The operation of the HOM couplers in the presenceof the operating electromagnetic field is assessed, quantifying thermaland multipacting behaviour.Finally, first measurements of crab cavity HOMs with proton bunchesare presented and compared with simulations. The measurementsare used to evaluate the accuracy of the methods used to calculateimpedance and HOM power. Several conclusions feed-back into ancillary design and acceptance criteria for future manufacture.
U2 - 10.17635/lancaster/thesis/743
DO - 10.17635/lancaster/thesis/743
M3 - Doctoral Thesis
PB - Lancaster University
ER -