DDS design status . Alessandro D’Elia. Outline. General overview of DDS working principle CLIC_DDS_A design status Towards CLIC_DDS_B: wakefield simulations and impedances HOM coupler design Some conclusion. Damped and detuned design.
rf couplerNLC/GLC DDS design
Ref: R. Jones, et al. , PRSTAB 9, 102001, (2006).
Error function distribution
Courtesy of R. M. Jones
Courtesy of V. Khan
The chose of the cell geometry is crucial to meet at the same time:
Surface fields in the specs
Consequences on wake function
Cell shape optimization for fields
Roundings enhance the magnetic field however a reduction of the slot size mitigates this enhancement and RF parameters are back within required limits. Also the wake damping is still in the limits with margins for a further improvement.
Wakefield calculations for DDS are, in the early design stage, based on single infinitely periodic cells. Though cell-to-cell interaction is taken into account to calculate the wakefields, it is important to study full structure properties using computational tools.
Lorentzian fit of the peaks
As a first approach I decided to reproduce the same as done at for NLC/JLC:
HOM coupler attached at first and last regular cells
Only Matching cells uncoupled
How much is the bandwidth?
Obviously this analysis is qualitative and in the build up we are neglecting the effect of the bunches on the following ones
My understanding is that, for first dipole band the most dangerous frequency is ~18GHz. Then I’m trying to match the HOM coupler at this frequency.
Same technique as for matching cells
No common minima yet @ 18GHz