The 5th video conference meeting for the SPL cavity working group took place on May 31st 2010.

Participants:
CERN: R. Garoby, F. Gerigk, S. Atieh, G. Arnau Izquierdo, S. Calatroni, P. Santos Silva, K. G. Lindell<o:p></o:p>

TRIUMF: R. Laxdal<o:p></o:p>

The proposed agenda was:<o:p></o:p>

·        Approval /follow up of minutes of previous meeting<o:p></o:p>

·        CERN Safety requirements for sc cavities and cryomodules (Phillip Miguel Santos Silva)<o:p></o:p>

·        Specification of niobium sheets (Said Atieh)<o:p></o:p>

·        Longitudinal HOM power estimations for pulsed beams (Wolfgang Weingarten)<o:p></o:p>

·        AOB<o:p></o:p>

·        Date of next meeting and agenda topics <o:p></o:p>

<o:p> </o:p>

Detailed discussions:<o:p></o:p>

·        Approval /follow up of minutes of previous meeting<o:p></o:p>

o    The minutes are approved<o:p></o:p>

·        CERN Safety requirements for sc cavities and cryomodules (Phillip Miguel Santos Silva)<o:p></o:p>

o   Philip gave an overview of the basic guidelines. It is stressed that even in the framework of worldwide collaboration the relevant applicable standards (ie pressure vessels) are the EU ones, and that equipment manufactured abroad should comply with those. If these are guaranteed, no destructive test is necessary. All manufacturing steps must be performed by qualified operators according to regulations. To a specific question, Phillip replied that the definition of the interface delimiting the pressure vessel (the cavity itself?) must be clearly stated in the design report<o:p></o:p>

·        Specification of niobium sheets (Said Atieh)<o:p></o:p>

o   The basic choices have been made: 3.5 mm thickness, square sheets, all tested by the manufacturer by US and/or eddy currents. Specifications are in line with DESY’s for RRR 300, reviewed by EN/MME. B. Laxdal reminds that at each machining / welding step a thickness of 20 microns is chemically removed. S.C. underlines that intermediate annealing during cavity forming should be avoided, or deep chemistry should be needed in order to avoid contamination diffusion. The amount of spare Nb to purchase has been discussed: 25% seems reasonable (4+1 5-cell cavity). It will be left to the cavity manufacturer to propose the fabrication of one (or more) single cell cavity as a fabrication test. Following a question on geometrical tolerances E. Chiaveri, contacted after the meeting, reminds that the choice of 0.2 mm for LEP cavities was due to frequency accuracy.<o:p></o:p>

·        Longitudinal HOM power estimations for pulsed beams (presented by Sergio Calatroni on behalf of Wolfgang Weingarten) <o:p></o:p>

o   W.W. included the duty cycle in his simulations: the dissipated power just scales with it, without introduction of other Fourier components. Discussions went on  as to the physical mechanism behind the decrease in radiated power at high Qext, for out-of-line modes. Beam noise tends to level this out for high detuning. The message conveyed is that high Qext could be the right way to go. It is reminded that plastic detuning-tuning of the cavity fundamental mode may help getting HOMs out of machine lines. <o:p></o:p>

·        AOB: none<o:p></o:p>

·        Next regular meeting will be skipped due to the SPL collaboration workshop. Following meeting  will be on July 26<o:p></o:p>