Minutes of the ICE section
40th meeting on Wednesday 28/09/2011 (08:40-10:30, 6/2-004)
ICE members: Benoit Salvant (BS), Christian Hansen (CH), Carlo Zannini (CZ), Hugo Alistair Day (HD), Elena Benedetto (EB), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Iadarola (GI), Giovanni Rumolo (GR), Jean-Luc Nougaret (JLN), Kevin Shing Bruce Li (KL), Nicolo Biancacci (NB), Nicolas Mounet (NM), Olav Ejner Berrig (OB), Tatiana Pieloni (TP), Werner Herr (WH), Xavier Buffat (XB).
Present/Excused: BS, CH, CZ, HD, EB, EM, EW, FS, GI, GR, JLN, KL, NB, NM, OB, TP, WH, XB, Alexey Burov, Georges Trad, Giuseppe Bregliozzi, Hannes Bartosik, Mike Barnes.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 39th meeting + Actions
- Will come soon.
3) General infos
- Discussion on impedance from NEG coating and roughness (also with FritzC by email) => ~ the same result is obtained if the NEG's layer is equal to the roughness depth (due to the distance between the induced charges and induced currents).
- SL meeting: No meeting last week.
- News on the LHC:
- Talk by Laurent Tavian at yesterday's LBOC on beam screen's heating => Seems OK in the arcs (meaning also the impedance should be fine) but seems that there is a factor ~ 2 more in the triplets => To be understood.
- Discussion this afternoon after the LMC with SteveM etc. to decide on the TCTP collimators (BS gave also a talk last week at the collimation design meeting).
- Floating LHC MDs being discussed, 24 h blocks, from week 39 to 42.
4) TDI heating and TDI8R observations since the last Technical Stop with added thermocouples (Giuseppe Bregliozzi for Vincent Baglin): pptx
- Both TDIs behave similarly during injection, they are sensitive to particle loss => At each injection, there are particle losses and small spikes.
- TDI8R has a systematic slow transient since beginning of May, with a delay of few hours after stable beams.
- Most of the time, TDI2L pressure decreases or is constant. However, some transients are occasionally observed since the beginning of August and confirmed since then.
- Following transient, equilibrium pressures are observed at both TDIs for long fills.
- During the TS 4, wk 35, the TDI.8R and TCTVB.8R were equipped with many thermocouples at several locations (note that the pressure is measured at TDI by VGPB.231.4R8.X).
- Transient pressure is correlated with temperature increase of at least 15 deg as measured at TDI8R extremity.
- A temperature increase of ~ 50 degrees increase the outgassing rate by one order of magnitude.
- MikeB mentioned several times that the thermal time constant is an important ingredient for the understanding and that we should try and have an estimate of it.
- Interesting discussion after the meeting (in the PS cafeteria) on the difference between impedance and ecloud effects:
- With an impedance: induced currents are responsible for the power loss / heating and as a consequence there is outgassing and pressure increase.
- With an ecloud: both ecloud formation (and therefore vacuum degradation) and heating happen at the same time (is it really the case? To be followed up).
5) Transverse constant wake field contribution (KL): ppt
- Scope: Constant transverse wake field kick when the beam axis and the electromagnetic axis are not congruential → transverse potential well distortion, beam takes on a banana-like shape.
- Example of an SPS extraction kicker magnet => Horizontal "constant" wake-field (in fact wake potential) from CZ. It seems there is a shift in the negative coordinate which needs to be understood (causality!) => Might not have a big influence for the rest of the talk (to be checked).
- Hamiltonian:
- Shifted harmonic oscillator,
- Neutral position shift.
- => Slide-dependent orbit distortion.
- Without synchrotron motion this leads to a flapping tail in phase space.
- With synchrotron motion this leads to an alternatively flapping tail and head in phase space.
- The slice emittance is preserved. Any non-linearities will cause the beam to thermalise and the emittance to increase.
6) Actions to be taken for the next meeting
- Old actions.
7) Miscellaneous
- The next (41th) meeting will take place on 12/10/2011 => Agenda:
1) Highlights from IPAC11 (IPAC participants) => Few slides on an activity of interest for the section (impedance or beam-beam etc.).
2) Summary of Fermilab's MDs (FS).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 02/10/2011.