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Minutes of SPL cavity Working Group meeting on 15 Nov. 2010
. Participants: CERN: R. Calaga, O. Capatina, E. Chiaveri, T. Junginger, M. Schuh, W. Weingarten.
Darmstadt: W. Mueller
Rostock: H.-W. Glock.
CEA-Saclay: S. Chel (no video connection)
The proposed agenda was
. Approval/follow up of minutes of previous meeting
. Magnetic shielding simulations for short cryomodule (T. Junginger)
. Qext estimations for the HOM hook coupler (HW Glock) . Open issues concerning the technical specification for the manufacture of SPL cavities . The minutes were approved without modifications. . T Junginger presented the most recent computations with Microwave Studio and compared them with approximative analytical formulae. His final proposal is: two passive shields, one inner shield per cavity, including an end cap, one outer shield per module, with 2 mm Cryoperm or Amumetal inwardly and 1 mm Mumetal outside. The magnetic field as measued in the SM18 bunker is less than 50 microtesla absolute value and is very inhomogeneous. The aim of the shielding consists to achieve less than 1 microtesla on the cavity surface. It was also mentioned that a company (Vacuumschmelze) may provide the shielding with the necessary heat treatment already included. Other shielding materials are A4K. Upon a question related to the effectiveness at low temperature, it was said that in the range mu = 10000 - 13000 the cryoperm has a nearly temperature independent permeability (to be checked by TJ!). The thickness of the shielding is still under debate, 1 mm could be sufficient. . HW Glock presented the status of the "hook" HOM coupler simulation, by using the method of "Coupled S-parameter calculation (CSC)". The results are still preliminary, because the cavity's right-left asymmetry was not yet taken into account, nor was the effect of the fundamental power coupler. The coupling to various HOMs decreases relatively steeply with frequency above 700 MHz, but are still too high for our needs (Qext < 105 were not yet achieved). [note added after the meeting: for more information consult the 5th SPL collaboration meeting's website, HWG's presentation: http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=109664] . As to the technical specification of the manufacture of cavities, WW mentioned that a discussion on tolerances has not yet taken place. However the drawings of the cavity model as received from CEA-Saclay define the dimensions after manufacture, i.e. before the chemical treatment etc., The company is requested to deliver the mechanical structure according to tolerances to be defined by CERN. All subsequent treatments are done at CERN. Possible relevant parameters are: the field flatness of cells, the frequency, the stamped cell contour, the cup axis offset, the cup axis tilt, and the linear dimensions. . Date of next meeting
Next regular meeting will be on 13th December (the meeting was cancelled and shifted to 24th January 2011).
WW 6/12/2010 |