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Wooldridge, E.

Paper Title Page
THPCH040 Linac Focusing and Beam Break Up for 4GLS 2871
 
  • E. Wooldridge, B.D. Muratori
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
 
  As part of the design for 4GLS the linac focusing and its effect on the beam break up (BBU) threshold have been studied. The choice of graded gradient focusing scheme is discussed and initial models of the focusing, using a triplet of quadrupoles between each of the modules within the linac, are presented. The quadrupoles were set-up in a defocusing - focusing - defocusing format with strengths of -1/2k, k, -1/2k. Using these models the BBU threshold was computed using available codes assuming a 9-cell TESLA cavity within the linac and a 7-cell design with HOM dampers. A sweep of the magnet strength with respect to the BBU threshold showed that there is an optimum setting.  
THPCH041 Alternate Cavity Designs to Reduce BBU 2874
 
  • E. Wooldridge
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
 
  An investigation was carried out on alternate cavity designs to decrease the effect of the higher order modes (HOMs) whilst maintaining the cavity accelerating gradient. The cavities were modelled in Microwave Studio and the number of cells per cavity and the number of cells per unit length were examined. HOM data from these models was used in beam break up (BBU) codes to calculate the threshold and the results are presented here. The cells of each cavity were slightly deformed alternately in the x and y planes so that the fundamental frequency of the cavity remained unperturbed, whilst minimising the HOM coupling between consecutive cells. Other patterns, such as alternating each deformed cell by several degrees, were also investigated. The data from these e-m models was also used in BBU calculations and their thresholds calculated.