Minutes of the LRFF Task Force
10th meeting on Tuesday 12/06/2012 (09:00-11:00 max, 6-R-018)
LRFF members: Alessandro Bertarelli (AlessandroB), Alexej Grudiev (AG), Benoit Salvant (BS), Elias Metral (EM), Fritz Caspers (FC), Giuseppe Bregliozzi (GB), Hugo Alistair Day (HD), Jose Miguel Jimenez (JMJ), Marco Garlasche (MG), Mike Barnes (MB), Olav Ejner Berrig (OB), Oleksiy Kononenko (OK), Oliver Aberle (OA), Ralph Assmann (RA), Raymond Veness (RV), Rhodri Jones (RJ), Roberto Losito (RL), Sergio Calatroni (SC), Stefano Redaelli (SR), Vincent Baglin (VB), Vittorio Parma (VP), Wim Weterings (WW).
Present/Excused: AlessandroB, AG, BS, EM, FC, GB, HD, JMJ, MG, MB, OB, OK, OA, RA, RV, RJ, RL, SC, SR, VB, VP, WW.
1) Comments on the last minutes + Actions
- None.
- Status of the VMTSA in 2012 compared to 2011 (VB):
- The vacuum spikes observed in 2011 are not observed anymore this year => Excellent so far!
- Maybe one should check the temperatures at the TDI.
- VB informed us that they are building a bench to perform impedance measurements.
2) Past impedances studies with the RF fingers for some collimators (AG): pdf
- AG explained the few slides in showed in 2005 during a Collimation Working Group meeting on "On rf-finger heating and trapped mode damping in LHC collimator".
- Only the LHC secondary collimator of phase 1 is discussed (i.e. TCS with carbon jaw). The results of the simulations of longitudinal and transverse impedances of trapped modes in LHC secondary collimator are summarized in the AB-Note-2005-042 RF (http://cdsweb.cern.ch/record/911962/files/ab-note-2005-042.pdf).
- AG simulated 1/4 of the structure => 7.5 RF fingers as we have 15 per jaw and 2 jaws. The distribution of the RF-losses on the RF-fingers due to longitudinal mode at 1.247 GHz is shown on slide 2. Note also that on the figure, we see also other RF fingers connected the flanges and which are fixed. The RF fingers are referred to as follows: #1 is on the side while #8 is in the middle of the jaw. The result is that the loss density is higher for 1 than 8. Note that the magnetic field goes around the RF fingers azimuthally.
- One discusses the RF fingers connecting the beam pipe and the jaw and the jaw moves.
- Gap simulated: from 60 mm diameter down to ~ 5 mm.
- Question raised on the heating of the RF fingers. There is no cooling on RF fingers but they are clamped to the jaw which is cooled => There is come cooling but it is not very effective.
- Ag-coating is 5μm thick what is "much" bigger than the skin-depth in Ag at 1.247 GHz which is 2μm => Can be considered as solid Ag for this particular frequency.
- The usual formula for power loss with Gaussian distribution has been considered for the power loss computation and the results are given in slide 3.
- Then AG wanted to have an estimate of the RF finger sliding contact resistance and found that we are not dominated by the contact resistance, which is much smaller than the rest (with Rc < 7.5 mOhm, which was a given number at that point => To be checked). The purpose of his slide on the sliding contact resistance was to show that if the contact resistance is within specification then there is no issue. Reminder: in HFSS, one cannot simulate contact resistance.
- The damping of the transition mode was finally studied by putting some ferrite or SiC rings. The conclusion at that time was that we don't need damping (as the power from beam loss was believed to be higher that this RF power loss), so nothing was done.
- Question from AlessandroB: how does it compare to recent results for new collimators? AlessandroB showed the picture from lhctcs__0016-vAD.pdf. MG is studying this subject form the thermal point of view and will include also the radiation power and not only the RF power.
4) Actions to be taken for the next meeting
- Old actions.
5) Miscellaneous
- The next (11th) meeting will take place on 26/06/2012 between 09:00 and 11:00 (max.) in room 6-R-018 => Agenda:
1) More information about the wake field suppressor in the LHCb VELO (Massimiliano Ferro-Luzzi, PH-LBD).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 26/06/2012.