Participants:
CERN: R. Calaga, O. Capatina, J. Chambrillon, E. Chiaveri, M. Schuh, W. Weingarten.
Rostock: H.-W. Glock.
CEA-Saclay: S. Chel, G. Devanz, J. Plouin.
 
The proposed agenda was
. Approval/follow up of minutes of previous meeting
. Towards the upgrade of the CERN SRF preparation and assembly stations at SM18 (J. Chambrillon)
. Towards the technical specification for cavities, helium tank and magnetic shielding (O. Capatina)
 
. The minutes were approved without modifications. H. W. Glock will briefly present new results on the HOM coupler design at the end of the meeting
 
. Towards the upgrade of the CERN SRF preparation and assembly stations at SM18
Wolfgang presented Janic as a newly recruited fellow being charged, as his first task, with the implementation of clean work conditions and diagnostic tools for quality assurance for the manufacture of SRF cavities. Janic gave a status of the present SM18 SRF clean room installation (slides attached). Based on recommendations given during the power coupler workshop*), according to experience in other labs, all assembly work of elements that are in connection with the cavity vacuum must be performed in a class 10 (ISO 4) clean room. Otherwise the envisaged acc. gradient of 25 MV/m cannot be guaranteed. There were questions about whether this is really necessary because the operator is the main source of contamination irrespective of the quality of the clean air. Janic responded that precautions will be foreseen to minimize the influence of the operator ( fog generator to visualize the air flow, local particle counter with alarm, overpressure by Ar gas injection for the protection of sensible surfaces from dust). Enrico recommended to establish a very detailed record for the sequence of actions to be taken in the clean room (no acting on impulse allowed). Janic was invited by Stephane to take into account the experience of Saclay in addition to that of DESY's (by joining in to the planned trips to Saclay and DESY). He also presented his plans for optical inspection (camera set-up developed at Kyoto University for KEK/DESY). His next task is a cost estimation of the proposed refurbishment of the SM18 clean areas.
 
. Towards the technical specification for cavities, helium tank and magnetic shielding
Ofelia summarized the planned objects to be manufactured (Nb cavities, Cu cavities, He tanks, cryo-module, etc.) as decided after the approval by the CERN Council of the new Medium Term Plan (MTP) including target dates, cf. her slides. (The MTP foresees a reduction of R&D related resources for the SPL study by about 1/3, but, on the positive side, states a firm commitment of CERN for the high power SPL in view of future neutrino factories). Only one copper cavity will be manufactured for HOM studies (so there will unfortunately be no 2nd Cu cavaity available for RHU in London, unless payed by them). Ofelia raised several questions on the recipe to be followed for the manufacture/processing of SRF cavities for the SPL study. The guideline for the first iteration was based on the sequence of treatments as developed at DESY for FLASH/XFEL. However, several steps have to be modified or adapted to our needs. They are, among others:
 
- will the electro-polishing (EP) be done at CERN?
Action: Sergio to give his advice on the details, availability, thickness of removal, etc.;
- will there be a 2nd EP needed after 800 °C annealing and tuning; advantage/disadvantage with respect to a buffered chemical polishing (BCP) or is high pressure water rinsing (HPWR) sufficient, as Rama proposes?
 - field flatness measurement to be done at industry or CERN? Preference for industry with CERN personnel and RF equipment;
- is baking at 120 °C, as at DESY, really necessary? For what reason?
- can the 800 °C annealing be done with NbTi flanges already mounted?
 
It was also said, that on the long term, we must learn and understand the rationale of any treatment step (e.g. what is the annealing good for? etc). We shall also adhere to the logic that the vertical test of the cavity is a qualification test for the surface, and that thereafter, if the cavity is performing according to the specification, no alteration of the cavity surface is allowed (i.e. no chemical or electrochemical treatment, but water rinsing or degreasing shall be possible).
As to the sequence as mentioned in her slides, the “3rd stage” (800 °C annealing) should be executed before the 2nd stage (test in cold cryostat).
Action: Wolfgang will contact DESY people to clarify these questions.
 
. AOB
- Hans-Walter reported on the recent RF simulations of the HOM coupler. The LEP/LHC "hook" coupler, as originally built, can only provide the notch filter at the fundamental mode frequency of 704 MHz after modification. The capacitance has to be made bigger. Hans-Walter is not convinced whteher this design is mechanically feasible. Action: He is invited to send the model to Ofelia for evaluation with the CERN design office. Hans Walter proposes a second version, without lHe dead end to be studied. Enrico mentioned the need to preserve dismountability of the HOM coupler. Rama added that at BNL a HOM coupler has been designed for 704 MHz, which should be looked at.
- A visit to Saclay is deemed necessary to conclude on the final drawings for the He tank
- Marcel announced that he has drafted a report on the HOM related discussions we had in this working group and elsewhere :
 
Date of next meeting
Next regular meeting will be on 18th October, a day before the short cryo-module review.
[P.S. This meeting was cancelled in between. So the next meeting will take place on the 15 November 2010. WW 5/10/2010]
WW 23/9/2010