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4GLS Cavity considerations for BBU

4GLS Cavity considerations for BBU. Emma Wooldridge Accelerator Science and Technology Centre. Ferrite Dampers Perturbed cavities Linac focusing. Ferrite Dampers. By including ferrite dampers near the cavity power can be removed from the Higher Order Modes

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4GLS Cavity considerations for BBU

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  1. 4GLS Cavity considerations for BBU Emma Wooldridge Accelerator Science and Technology Centre

  2. Ferrite Dampers • Perturbed cavities • Linac focusing ERL’07, 21st to 25th May 2007 Emma Wooldridge

  3. Ferrite Dampers • By including ferrite dampers near the cavity power can be removed from the Higher Order Modes • Dampers are placed on each end of the cavity at 80K to minimise cryogenic load • In a module dampers alternate diameter between larger and smaller ERL’07, 21st to 25th May 2007 Emma Wooldridge

  4. Dampers continued • Tiles are made from three different materials, each optimised to absorb HOMs at different frequencies. • One good at low frequencies <10GHz (Ferrite TT2-111R) • One good at middle and high frequencies >10GHz (Ferrite HexMZ) • One good at higher frequencies >25GHz (Ceramic ZR20CB5) ERL’07, 21st to 25th May 2007 Emma Wooldridge

  5. Effect of Dampers on the BBU threshold • Basic model created with two loops of TT2-112R ferrite • Increase in BBU threshold of around 30% ERL’07, 21st to 25th May 2007 Emma Wooldridge

  6. Altering the Cavity • Introduce small defects in each cell to split the degeneracy of dipole modes • Early results suggest that alternating the perturbation in x then y produces significantly higher thresholds • Further tests required • Could this be errors in the model or a real effect? ERL’07, 21st to 25th May 2007 Emma Wooldridge

  7. Linac Focusing • Three linac focusing schemes designed with • Singlet • Doublet • Triplet of quadrupoles between each module ERL’07, 21st to 25th May 2007 Emma Wooldridge

  8. Linac Focusing Continued 1 ERL’07, 21st to 25th May 2007 Emma Wooldridge

  9. Linac Focusing Continued 2 • Idealised recirculation used in all threshold calculations • K value of the magnets scanned to find optimum value • Tesla 9 – cell cavity HOMs used • Will be updated as the 4GLS lattice design settles ERL’07, 21st to 25th May 2007 Emma Wooldridge

  10. Future Work • Investigate the HOM damper • Model realistic damper and investigate effect on BBU threshold • Verify cavity perturbation results ERL’07, 21st to 25th May 2007 Emma Wooldridge

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