Minutes of the SPL steering group (draft )

meeting no. 7

date: 14 March 2008

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

Agenda

1. General news and facts
2. Cryo-modules for different frequencies and at different temperatures (V. Parma)
3. Review of maximum surface fields at JLAB (S. Calatroni)
4. Round table
5. Next meeting

1. General news and facts

• a half day SPL review meeting will take place on April 30th, Dave McGinnis from FNAL has accepted an invitation to attend. In the morning Dave is asked to give a talk on the status of Project X.
• the main goal of the review meeting will be the frequency and cryogenic temperature of the SPL.
• the preliminary schedule for the afternoon meeting is:

Status of analysis of SPL RF frequencies and cooling temperature
Wednesday, 30 April 2008, CERN building 864/1-C02

title	subject	speaker
Cryogenics	Consequences of tunnel slope, cryo-module design, possibility to reuse ILC/XFEL experience	V. Parma
Discussion, other arguments, criteria, optimisation	how far are we from making a choics, which criteria, open questions	all
Introduction	Characteristics of the different SPL implementation stages, design constraints, meeting goals	R. Garoby
Potential linac architecture & beam dynamics	several (frequency) options for the layout and their impact on beam dynamics	F. Gerigk/A. Lombardi
RF frequency	impact on RF hardware	E. Ciapala
SC cavities	performances and overall efficiency as a function of temperature and frequency	W. Weingarten + S. Calatroni, F. Gerigk
Wrap-up		R. Garoby, F. Gerigk

2. Cryo-modules for different frequencies and at different temperatures (V. Parma)

• If possible one should avoid the use of superfluid helium (<2.17 K) in order to reduce the complexity, cost, maintenance effort,
• At 704 MHz it now seems that there is no point going to superfluid helium, at 1408 MHz in pulsed operation it seems necessary but must be studied in depth (tests!) if one really needs to be < 2.17 K.
• For 704 MHz, 4.5 K the cavities can probably fit into the ILC outer tubes, but it is likely that most of the openings will change position. However, to take into account the slope of the tunnel the interior of the tubes (helium vessels, pumping pipe, shielding) will have to be completely re-designed, so that there will be little benefit from ILC/XFEL work. Probably one can reduce the size of the pumping pipe, but then one has to make sure that the structural stability is still sufficient. Also, there may be a risk of helium dripping down the slope in one direction, while the gas is pumped in the opposite direction.
• Conclusion: at 704 MHz, 4.5 K it is very unelikely that we can profit from ILC/XFEL work on cryo-modules, at 1408 MHz, 2.1 K a reuse of this design is very likely,

3. Review of maximum surface fields at JLAB (S. Calatroni)

G. Ciovati from JLAB made a summary of cavity test data for S. Calatroni, which was distributed to the steering group members. The summary should not be distributed any further. S. Calatroni presented the main findings on a few slides ( pdf, ppt ), which show that the maximum surface fields reached with BCP treatment at JLAB were between 31 MV/m (field emission onset) and 44 MV/m (average peak surface field). Electropolishing and baking can increase these values by 20%. At DESY up to 40% better results have been achieved but it is not completely clear where the differences in the procedure are.

It was also found that the maximum peak fields for single and multi-cell cavities do not seem to be different. However, the success rate can vary considerably and confirm that it is much easier to get high gradients out of a single cell. E.g. 70 MV/m were achieved with 30% success rate, 50 MV/m with 80% (1300 MHz).

4. Round table

• A. Lombardi reported that first test have been made for the SPL layout, which changes from 352 to 1408 MHz. It seems that the transition energy has to be shifted from 160 MeV to 250 MeV to achieve acceptable beam performance. Further simulations will be done.

5. Next meeting

will take place on April, 11th 2008, 16:00 in 865-1-D17

-- FrankGerigk - 26 Nov 2007