Minutes of the LRFF Task Force
8th meeting on Tuesday 29/05/2012 (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
- Nice poster from Mark Antony Gallilee et al. at IPAC12 on new design for RF fingers => To be invited at some point (certainly next meeting).
- Review of ferrite in all the groups => Next meeting.
2) Longitudinal impedance simulation studies of VMTSA (OK): pptx
- HFSS used to try and benchmark the CST simulations made in the past by BS, who found some strange results in some cases with very low Q-factor.
- tet10 means tetrahedral with 10 points.
- Setups to be simulated:
- Conforming old fingers.
- Conforming new fingers.
- Wire, no fingers.
- Bad contact, 1st type.
- Bad contact, 2nd type.
- Ferrites IN, Philips 8C11.
- Reminder from AlessandroB: Put the ferrite (with grade) used in the drawings for better traceability in the future => Good idea indeed.
- On slide 4, in red => Simulations done and in green => Being done.
- 1) Conforming new RF fingers:
- First 2 modes (which seem to be physical) => Consistent with CST.
- For other modes (still to be checked) => Looks like numerical noise.
- Of course for this (perfect) case no ferrite is needed.
- Reminder: It is very difficult to simulate bad contacts => What can we do in the future?
- Reminder: The VMTSA issue was discovered by X-rays because they were looking for an aperture restriction.
- Reminder from RV: A note from L. Vos (Power losses in enlarged experimental chambers of the LHC) where it was decided not to damp the trapped modes, relying on the thermal expansion.
- 2) 2nd type bad contact (10 mm gap):
- Frequencies seem consistent.
- Q factors were suspicious from BS (with CST, as they were very low) and they are much higher with HFSS.
- Large shunt impedance R => 6 kW power loss expected!
- 3) With wire and no RF fingers:
- Good agreement with CST, HFSS and measurements.
- Conclusions:
- Good experience simulating RF Fingers in HFSS and convergence still to be checked for some simulations.
- It looks like CST gives incorrect Q-factors and shunt impedances for some cases. Convergence problem?
- Ferrites simulations must be accomplished.
- Next step (discussed during the meeting): Simulate with HFSS the case of the VMTSA with the old RF fingers and in particular the wire measurements done to try and benchmark these results.
- Paper from RV: Development of a bellows assembly with RF shield for KEKB (K.Kanazawa and Y.Suetsugu).
- MG => Can you look at the thermal evolution with this huge power loss?
- Reminder: Talk by VB where we saw some melted pieces in the VMTSA.
3) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (OK): Continue the simulations of the VMTSA with old RF fingers (instead of new RF fingers) with HFSS to try and benchmark the wire measurements made in the past.
- Action 2 (MG): > 6 kW of power loss were predicted by OK for the VMTSA 2nd type bad contact (10 mm gap) with the new RF fingers. What about the thermal evolution with this huge power loss?
4) Miscellaneous
- The next (9th) meeting will take place on 05/06/2012 between 09:00 and 11:00 (max.) in room 6-R-018 => Agenda:
1) Some pictures of the wake field suppressor in the LHCb VELO (EM),
2) New design for RF fingers (Cedric Garion and Mark Gallilee, TE-VSC-EIV),
3) (First) review of ferrites used at CERN to damp HOMs: references, manufacturers, thermal treatments, etc. (all the groups: TE/VSC, EN/STI, TE/ABT, BE/RF, BE/BI, BE/ABP, EN/MME etc.) .
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 04/06/2012.