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DDS design status. Alessandro D’Elia on behalf of Roger M. Jones. CLIC_DDS_A. 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
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DDS design status Alessandro D’Elia on behalf of Roger M. Jones
CLIC_DDS_A • 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)
CLIC_DDS_A last cell from VDL VDL BODYCOTE
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
First steps toward CLIC_DDS_B 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.
Comparison of fsyn, Q’s and Kicks <QloadGdfidL>=1947 <Q Circuit Model>=1647
Reflections only from one side of the structure Ref_down=0, Ref_up=1 Ref_down=Ref_up=0 (Original wake) Full Structure (8-fold interleaved) Ref_down=1, Ref_up=0 Ref_down=Ref_up=0 (Original wake) 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.
A possible geometry for the HOM Coupler • J. W. Wang and al. “Progress toward NLC/JLC prototype accelerator structure”, LINAC04 Port2 Port1 Port4 Port3 SLAC PEC PML As a first approach I decided to reproduce the same as done at for NLC/JLC: HOM coupler attached to the first and last regular cells Only Matching cells uncoupled
HOM coupler matching technique OLD S11@17GHz NEW
Fields Even odd 17GHz 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
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)
