4GLS Cavity considerations for BBU

Emma WooldridgeAccelerator Science and Technology Centre

ERL’07, 21st to 25th May 2007Emma Wooldridge

Ferrite Dampers Perturbed cavities Linac focusing

ERL’07, 21st to 25th May 2007Emma Wooldridge

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 2007Emma Wooldridge

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 2007Emma Wooldridge

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 2007Emma Wooldridge

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 2007Emma Wooldridge

Linac Focusing

Three linac focusing schemes designed with Singlet Doublet Triplet

of quadrupoles between each module

ERL’07, 21st to 25th May 2007Emma Wooldridge

Linac Focusing Continued 1

ERL’07, 21st to 25th May 2007Emma Wooldridge

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 2007Emma Wooldridge

Future Work

Investigate the HOM damper Model realistic damper and investigate effect on

BBU threshold Verify cavity perturbation results