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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• Morikawa is going to produce a stack of 10 cells reproducing the last regular

cell in order to fix machining procedure (mid September): a big thank to CLIC Structure Mechanical Design Group who supervised, together with KEK, the technical design during these last months

• There is the intention of performing RF measurements on this stack of cells: to be agreed with KEK

• High Power Tests are foreseen as soon as we will get the full structure (end of this year)

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CLIC_DDS_A last cell from VDL

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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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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Reflections only from one side of the structure

Ref_down=0, Ref_up=1Ref_down=Ref_up=0 (Original wake)

Ref_down=1, Ref_up=0Ref_down=Ref_up=0 (Original wake)

Full Structure (8-fold interleaved)

Circuit Model shows that only one HOM coupler downstream is enough. Further analysis shows also that the matching band must be centered @17GHz. The full band can be mapped out and this is ongoing.

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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

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

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HOM coupler matching technique

OLD

NEW

S11@17GHz

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Fields

odd Even

The field is flowing from one coupler to the other (low reflections) independently on the electrical length of the structure. A further improvement is still possible but what matters now is to map out the full reflection band

17GHz

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Conclusions• CLIC_DDS_A: despite of the tremendous events in Japan, Morikawa and KEK are

able to start the cell production• CLIC_DDS_A: we expect the first stack of 10 cells (all equal 24th regular cell stack)

for mid/end September • CLIC_DDS_A: RF measurements on this stack of cells to be agreed between

Manchester and KEK• CLIC_DDS_A/CLIC_DDS_B: compared analysis of the wakefields in GdfidL and

Circuit Model done for CLIC_DDS_A (presented in an IPAC11 paper)• CLIC_DDS_B: previous point confirms the reliability of the Circuit Model from

which the fundamental parameters to design CLIC_DDS_B as well as HOM couplers, will be derived

• CLIC_DDS_B: Study and design of the HOM coupler started• CLIC_DDS_B: Further studies on the impact of the wakefields on beam dynamics in

CLIC started (Inna Nesmiyan, Manchester PhD student)