Minutes of the LRFF Task Force
7th meeting on Tuesday 08/05/2012 (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 + VittorioV.
1) Comments on the last minutes + Actions
- Should come soon.
2) Equipment review: some equipments from TE/ABT (MB and WW): pptx
- All the infos has been summarized at http://emetral.web.cern.ch/emetral/LRFF/InfoOnLHCEquipmentsWithRFfingers/RFContactFingersInLHCABTEquipments/RFContactFingersInLHCABTEquipments.htm.
- Mike => MKI:
- 320 deg bake-out, ~ 100 h (slowly 5 deg / h usually).
- ~ 3m long tube of Al2O3 etc. => Thermal expansion of SS 403L tank of 17.3 microm / m deg.
- RF fingers have to accomodate at max 17 mm.
- SS RF fingers instead of CuBe due to Sergio's picture on stress.
- Old RF fingers (based on PIMs) for 7/8 installed MKI. 17 RF fingers with 6 mm gap (for pumping of tubes).
- Spacing between RF fingers larger than PIM for pumping.
- Injected beam in the ceramic and circulating beam in one of the 2 pipes on the sides.
- New RF fingers (design based on warm interconnects) => MKI2.B installed during TS in 2010-2011, because of some few breakdown. The new MKI that could be installed in August will have these RF fingers. 36 RF fingers with 1.59 mm gap (for pumping of tubes)
- We had 2 breakdown in April this year with the MKID.
- Main motivation to change the design of the RF fingers:
- Due to the 8 mm (or worse 17 mm) needed which would lead to some deformation with the old type and they thought it was better to have sliding contacts.
- There is a spring for the new RF fingers and not for the old.
- 3 contributions in the real part of the longitudinal impedance: 1 part is coming from the capacitive coupling (leading to some resonances), 1 from the RF fingers etc. leading to another set of resonances and the 3rd is the leakage of the fields to the ferrite leading to the broad-band behaviour => the main part is coming from the ferrite.
- If the spring is lost, it opens a gap to the vacuum tank and then low frequencies can appear.
- Inside of the tank is quite shiny, with very poor emissivity => Plan to increase it.
- VittorioV mentioned that we are below cut-off and that there could be a larger resonance in reality (could be factor 5) => VittorionV will present that in the future.
- VincentB mentioned that we have 3 types of heating from measurements => Can we understand something?
- This is coming from my Chamonix2012 talk, page 39: MKI2, MKI8 and MKI-8D and 8 which are heating more.
- Only 1 MKI with 24 (15 full line and 9 are short) and all the others are 15 => We cannot disentangle.
- MikeB mentioned that the only reliable measurements is coming from the strength of the kicker.
- Another reason could be the emissivity of the tank and maybe 1 or 2 have a lower one.
=> Should work on 3 points:
1) Increase strip number.
2) Increase the emissivity. Assuming the power loss of Hugo and the ferrite heating would lead to a value of emissivity very close to 0.1.
3) Be careful of the RF fingers.
- MKI dissipation vs. the number of conductors => Going to 19 (out of 24) would already help a lot.
- Radiography of installed MKI RF fingers is difficult (poor access due to valves, etc) – hence results are inconclusive.
- Even with the new RF fingers, the real part of the longitudinal impedance goes up after bakeout.
- WW => TCDS - TCDQ:
- point 6, beam dump extraction.
- All tanks have undergone a bake-out cycle of 24h@300ºC in an oven. Furthermore, they are baked in the tunnel @250ºC.
- In the TCDS, Circulating beam on the right, and extracted on the left. Graphite, CC, etc. for the absorber block in the middle.
- Again spring and if it is gone there is nothing to contain it.
- We don't expect movements.
- In the TCDQ we don't have the extracted beam. 0.7 mm gap of the blocks => All this has been simulated in the past by AlexeyG (will be reviewed in a future meeting).
- There is cooling but there is no noticeable heating observed. Cooling capacity should be 1 kW (tbc by WW).
- TCDS is static while the TCDQ is moving while ramping close to the beam (~ 15 mm from the beam at injection and ~ 5 mm at top energy).
- Proposed upgrade for LS1. VB mentioned that we have issues with losses in point 6 on Q4. Is it linked to this? Yes. TCDQ has never been upgraded (the TCDS was installed in the past after discover that it was not enough for the nominal beam). Right now, what is the limitation? 1.4E11 p/b with 25 ns at 7 TeV. In case of asynchronous dump we could destroy the graphite blocks.
- TCDQM and TCLIM:
- No RF fingers with seal.
- VMTAB => Big bellows. There should be a spring. Bellows accomodate misalignments => Look at the design. Very long RF fingers. Large movements laterally so this is very critical!!! We have a spare and we should measure it (see Action 1 below).
- Installed VMTAB bellow in 4R6, showing problem with bulged out contact fingers.
- Summary of the ABT equipments:
- WITH contact fingers:
- Injection MKI: Contact fingers between tank & ceramic chamber and between tank & copper chamber.
- Extraction TCDS: Contact fingers between tank & Absorber.
- Extraction TCDQ: Contact fingers between tank & absorber and between beam screen & absorber blocks; Special Bellow VMTAB.
- WITHOUT contact fingers:
- Injection TCLIM and Extraction TCDQM: No contact fingers, Cu metallisation of the St. Steel chamber.
- Extraction MKD and Measurement MKQ: No contact fingers, Ti metallisation of ceramic chamber directly connected to flanges.
- Extraction MKB: Not on the circulating beam, no metallisation, no contact fingers.
3) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (HD and OB): Perform a bench impedance measurement of the VMTAB module with a wire.
4) Miscellaneous
- The next (8th) meeting will take place on 29/05/2012 between 09:00 and 11:00 (max.) in room 6-R-018 => Agenda:
1) Some impedance results (OK).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 28/05/2012.