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DDS design status

Alessandro D’Elia on behalf of Roger M. Jones

CLIC_DDS_A

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• In October 2009 it has been decided to produce a first prototype to be tested at input power of 62 MW to ascertain the suitability of the structure to sustain high e.m. field gradients

• RF and mechanical design completed in Summer 2010• 4 qualification disks machined by VDL received in Oct

2010• The 4 disks have been successfully bonded by Bodycote• The whole structure will be machined in Japan by

Morikawa under the supervision of KEK• High Power Tests are foreseen as soon as we will get the

full structure

CLIC_DDS_A

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CLIC_DDS_A some further detail

VDL

BODYCOTE

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CLIC_DDS_B

• The study of a further structure (CLIC_DDS_B) is already started

• This structure will be based on CLIC_DDS_A but will be provided with HOM couplers and with a compact coupler for fundamental mode

• Both wakefield suppression and high power performances will be tested

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First steps toward CLIC_DDS_BWakefield 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.

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Comparison between GdfidL and Circuit Model

NB: GdfidL does not include Ohmic losses which are present in Circuit Model

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Recalculation of Kicks and external Q’s from the impedance

Lorentzian fit of the peaks

QextKick factor

Procedure

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Introduction of Ohmic Q in GdfidL reconstructed wake

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Comparison of fsyn, Q’s and Kicks

<Qload GdfidL>=1947<Q Circuit Model>=1647

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As a first approach I decided to reproduce the same as done at for NLC/JLC:1) HOM coupler attached at first and last regular cells2) Only Matching cells uncoupled

PEC PML

Port1Port2

Port3

Port4

SLAC

A possible geometry for the HOM CouplerJ. W. Wang and al. “Progress toward NLC/JLC prototype accelerator structure”, LINAC04

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Reflections only from one side of the structure

RPrimen=0, RPrime1=1RPrimen=RPrime1=0 (Original wake)

RPrimen=1, RPrime1=0RPrimen=RPrime1=0 (Original wake)

f=1.9874GHz8-fold, 3.48 (Original structure)

Circuit Model shows that only one HOM coupler downstream is enough

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HOM coupler matching technique

Same technique as for matching cells

No com

mon m

inim

a yet

Conclusions

• Due to tremendous earthquake in Japan, we had some delay in CLIC_DDS_A production; which will be terminated for the end of this year

• Comparison between circuit model and GdfidL is done showing a very similar behavior

• Studies on HOM coupler for CLIC_DDS_B are ongoing

• Studies on a structure with a lower Q in order to minimize the number of interleaved structures and to relax the requirements of the HOM coupler