Minutes of the SPL steering group

meeting no. 10

date: 6 June 2008

present: O. Brunner, E. Ciapala, R. Garoby, F. Gerigk, R. Losito, V. Parma, C. Rossi, M. Vretenar, W. Weingarten
excused: A. Lombardi, S. Calatroni


1. General news and facts
2. Cost optimisation (W. Weingarten)
3. Beam loading and power consumption (F. Gerigk)
4. Round table
5. Next meeting

1. General news and facts (R. Garoby)

  • RG asked if we can get a 704 MHz elliptical cavity from Saclay, and they offered a 1-cell low-beta cavity. SC confirmed that this would be an interesting test object and so we will try to get this cavity.
  • RL mentioned that he has a 200 W wide-band amplifier, which could cover 704 MHz and which would be sufficient for single cavity tests.
  • RG will contact INFN if they have other 704 MHz cavities, which could be used for tests and surface treatments at CERN.
  • RG has requested budgetary numbers from VP and SC to establish how much more funding we need to re-establish R&D on SC cavity treatment and testing at CERN and to finance 6 more cavities for the planned SPL-type cryo-module.
  • From the money that is available from the white paper (3 MCHF), some money was shifted from high-power modulator development at CERN towards cavity development at CERN. There is a chance that the modulator development can be done outside CERN (e.g: UK or US).

2. Cost optimisation (W. Weingarten)

A verification of the underlying physics models was made, which is used in WWs cost optimisation tool and the one which was used to calculate the numbers in the last SPL yellow report. For this purpose Frank and Wolfgang both simulated a defined part of the SPL using the same low- and high-power duty cycle with the same currents and cavity parameters for 704 and 1408 MHz. WW presentation summarises the calculated values for the RF power (at the point where it enters all cavities) and the cryogenics power for a 2K system (normalised to cooling power at 4.5 K). For the HPSPL the numbers are basically identical, while for the LPSPL there remains a differences in cryo-power, which could not be explained. However, since the parameters of the HPSPL will be used to optimise the facility, it was felt that we can be confident that WWs optimisation tool is perfeclty suited for the task.

Furthermore WW has included a field dependent Q-slope in his tool, following a forumula that was provided by SC. The formula matches well the measured curves for several cavities but there was a difference when comparing with an electro-polished 508 MHz cavity from KEK, where the actual measurements show higher Q values than the formula. It was concluded that the formula is probably too pessimistic for electro-polished cavities. Taking into account the Q-slope one finds a sharper decline in the grid-beam transfer efficiency for rising cryogenic temperatures, especially in the case of 1408 MHz.

3. Beam loading and power consumption (F. Gerigk)

FG calculated the beam loading in the SPL SC cavities for the various chopping schemes, which are under discussion for a neutrino facility. He showed that even for exotic chopping schemes there will be only negligible effects on the cavity voltage (variation <0.04% for both frequencies). Even though the voltage swing is always ~twice as high for 1408 MHz than for 704 MHz, the impact on the beam will be negligible. For Linac4 the maximum voltage swing was found be ~0.3%, which is still below the expected 0.5% for the PIMS, which is expected for injection into the PSB with 222 filled and 133 empty buckets.

The results of the comparison of power consumption numbers for the SPL (see WWs presentation above) highlighted that operation at 704 MHz will need approximately 30-40% more RF power than operation at 1408 MHz. The cryogenics power (assuming 2K for both frequencies) rises by more than 70%!

4. Round table

SC sent a few notes prior to the meeting, because he was unable to attend:
  • could not find, either in JLAB, SNS or INFN-MI a 800 MHz RF amplifier available for lending to us
  • The proposal from S. Chel to lend us a single cell 700 MHz cavity is very good. Always better to start with single cell and then move on to multicells. However we should still keep open the JLAB offer (for the SNS 805 MHz cavity).
  • Sent Wolfgang the new formula for the RBCS(E,T) that he should use for his new calculations
  • Made a quick budget estimate for electropolishing of SPL-type Nb cavities and sent to RG. In this budget estimate I forgot to mention that in the FP7 request regarding quarter wave Nb/Cu cavity development we have asked for money for the EP computer simulation program.
  • Info related to the Nb/Cu FP7 request. It should be mentioned that all the (electro-polishing) hardware (in the request) will be adapted to copper and not niobium, so it will not be compatible

RF stressed that we should have a draft summary of the recent SPL review for the next steering group meeting on July, 11th. Around 4 pages from every one should be enough.

Conference papers: there will be a general SPL paper at Linac'08 and the summary of the review and the final SPL choice for HB'08. There should be several contributions for SCRF'09 in Berlin.

5. Next meeting

July 11th, 2008, 16:00 in 866-1-D15

next general SPL meeting July, 4th 2008, 9:00 in 354-1-001

-- FrankGerigk - 09 Jun 2008

Topic attachments
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PDFpdf SC-cav.pdf r1 manage 756.4 K 2008-06-13 - 16:48 FrankGerigk  
PDFpdf SPL_steering_group_June08.pdf r1 manage 1313.5 K 2008-06-13 - 15:54 FrankGerigk  
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