Minutes RF structure meeting on PIMS mechanics 10.04.2008

present: P. Bourquin, G. Favre, F. Gerigk, J-M. Lacroix, I. Sexton, M. Vretenar, R. Wegner

excused: R. De Morais Amaral, Eric Page, Giovanna Vandoni

news & facts:


  • after several optimisation steps Ricardo sent us his latest results, which indicate that i) one does not need to cool the cylinders, cooling on the discs is sufficient, ii) the increase in temperature yields frequency changes that are well within the tuning range (verified by Rolf), iii) the maximum material stresses are in the range of 35 MPa,
  • these simulations were done assuming an RF duty cycle of 10%, whereas according to the lates scenarios for a high-power SPL it is unlikely that Linac4 will ever operate at duty cycles higher than 6%,
  • water flow is at 300 l/s per module, 1.4 m/s with a constant water temperature of 21 deg in the simulations,


  • according to Stephano Sgobba, the yield strength of the copper (where we have omitted the last forging step) is expected to be in the range of 40 - 60 MPa, if the last forging step is added (standard CERN specifications) then we can have a yield strength in the range of 200 - 240 MPa,
  • considering than we can reduce the applicable duty cycle by a few %, it was agreed with Maurizio that we still assume that the reduced copper specs are safe enough, Pierre came to the same conclusion,
  • now that it is clear that all brazing operations can be avoided, Pierre will look at the required thickness of the copper cylinders. It is expected that the thickness can be reduced, which will save material and make the welding simpler,


  • Eric Page has sent his requirements for the vacuum system to Jean-Michel: 2 pumping ports for each structure at the radial outer surface of the end-cells, and 2 small ports in the vacuum pipe in between the cavities for measurements,
  • probably using one pump/cavity for Linac4 will be sufficient,


  • Gilles pointed out that the structure can not be cleaned after the welding to avoid that liquids get trapped in the internal slots next to the e-beam welding, and that
  • the current support of the e-beam welding machine can only support ~600 kg, which is not enough for the PIMS,
  • Jean-Michel will give us an updated estimate of the weight soon,
  • the structure will be measured (low-level RF and metrology) before the welding,
  • a PIMS prototype needs to be constructed at CERN to make sure that all technologies are mastered and known here, for this we will use the high-quality copper, which is already ordered for the prototype,


  • construction of the series has to start in the middle of 2010 (see planning), which means that ideally the PIMS prototype should be ready for testing in the beginning of 2009, so that there is still a possibility to modify the drawings for the series construction.
  • The copper for the series production is expected to arrive at the end of 2009/beginning 2010 and a final order has to be given at least 6 months in advance.
  • planning for PIMS series production:


next meeting

8. May 2008, 10:00 in 6-2-002

minutes by Frank Gerigk

-- FrankGerigk - 11 Apr 2008

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