Minutes of the ICE section
90th meeting on Wednesday 28/08/2013 (08:40-10:30, 6/2-004)
ICE members: Adrian Oeftiger (AO), Andrea Passarelli (AP), Benoit Salvant (BS), Carlo Zannini (CZ), Danilo Banfi (DB), Daria Astapovych (DA), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Iadarola (GI), Giovanni Rumolo (GR), Javier Barranco (JB), Kevin Shing Bruce Li (KL), Nicolo Biancacci (NB), Nicolas Mounet (NM), Olav Ejner Berrig (OB), Serena Persichelli (SP), Sergio Rioja Fuentelsaz (SRF), Tatiana Pieloni (TP), Werner Herr (WH), Xavier Buffat (XB).
Present/Excused: AO, AP, BS, CZ, DB, DA, EM, EW, FS, GI, GR, JB, KL, NB, NM, OB, SP, GuidoS, HannesB, JosephK, SimoneG.
1) Newcomers / visitors
- AlexeyBurov will be at CERN from 22/09/13 to 05/10/13.
- Valeri Lebedev should be at CERN from 08/10 to 15/10 (ELENA review on 14-15/10/2013).
2) Comments on the minutes of the previous 89th meeting + Actions
- No comment.
3) General infos
- No particular comment from anyone.
- SL meeting => No meeting last week.
- News from LHC => Follow-up of nonconformities with RF fingers / contacts (BS):
- Endoscopy of the interconnect QQQI.2R5 (EDMS: 993108) performed:
- It seems that the situation did not change since the last endoscopy in 2009: 4 contacts are still sticking out on the bottom external side of the pipe and it does not look like it got worse.
- Carefully looked for stripes on the beam screen surface, but it was not obvious that there were any.
- During endoscopy done from IC QBBI.A20R3 deformed contact strips protruding into aperture were found in IC QBBI.B19R3 => See picture.
- ~ 150 PIMS already opened during LS1.
=> All nonconformities to be discussed at some LBOC meetings (currently foreseen on 03/09/13).
- Idea / suggestion from Alexej Grudiev to try and increase transverse Landau damping in the LHC (if needed) => Could an RF quadrupole be useful for this? This would introduce a linearly z-dependent transverse betatron tune (a nonlinear dependence could also be created by using higher frequency) => Action 1 below.
- Anthony Hawkins internship for few months (as discussed last time)? => In contact with BS.
- DariaA => Talk at ICE meeting on 11/09/13.
- PS LIU TDR started by MauroM and finalized by BS et al. and sent to SimoneG.
4) PS TFB kicker (97) measurements (Guido Sterbini): pdf
- GuidoS reported about all the very nice measurements performed on the HW of the PS TFB (Transverse FeedBack) system. A second talk should come later about beam-based measurements and a thid one about the comparison with simulations. Seems that we learned a lot on this (important) system (many thanks GuidoS et al.!) in particular for LIU (as acknowledged also by SimoneG). Furthermore, as discussed already in the past (and as will be discussed in more detail in the future), the system proved to work beautifully last year, damping in particular the head-tail instability at injection for all the cases studied. Finally, from the theoretical and simulation side (as will be discussed in the future by KL), a lot of progress has been done over the last year and one should be therefore in good shape to perfom all the comparisons with measurements (even if a lot of detailed studies remains to be done to fully understand the effect of the TFB on the beam dynamics).
- 2 possibilities for the PS TFB:
- 1 PU (in 98) + 1 kicker (in 97) => Beam has to go from 98 to 97 (i.e. 99/100 of the PS circumference) whereas the signal has to travel only ~ 1/100 of the PS circumference (in the opposite direction to the beam).
- 2 PUs (in 98 and 02) + 1 kicker (in 97).
- Kicker has 4 plates (inner and outer).
- Damping time (adiabatic approximation): tau (f) = 2 Trev / G (f), where G (f) is called the gain (knowing is allows us to determine the damping time of the system for all the beam spectrum).
- For the moment, the gain cannot be varied during the cycle but this should change in the future.
- Reminder:
- DSPU is controlling delays and phases => Heart of the system.
- Notch filter ON for all the revolution frequency lines.
- Hilbert filter ON for the dephasing to obtain the correct (cosine) function at the entrance of the kicker.
- Observation: Dephasing is not orthogonal to the setting of the gain here as a change in the dephasing also changes the gain.
- GuidoS presented all the detailed measurements performed on all the equipment:
- Kicker (coupling H-V between plates, kicker, 125-Ohm cables and 50-Ohm resistor),
- 50-Ohm resistor,
- Matching Network,
- Power
amplifier,
- Power divider,
- Power combiner,
- Pre-amplifier,
-
DSPU,
- PUs.
- Conclusions:
- It seems that all the devices have a natural BW (defined as
usual at - 3 dB) limit at ~ 100 MHz without a significant phase rotation BUT the
DSPU and the PU present the stringent BW limitations (~ 30 and ~ 60 MHz
respectively => the limit at ~ 20 MHz of the power-amplifier is not discussed
here as it is currently being imrpoved). Possible solution are using 2-3 DSPU
and up-down mixing and using normalised PUs signals.
- Minor loss of
transmission observed at high frequency on the kicker when using the 125-Ohm
cable => Plan to replace the 125-Ohm coaxial cables with 100-Ohm ones.
- The
choice of 100 MHz for the new amplifiers is compatible with most of the HW.
-
At the moment we cannot change the loop gain in the cycle => New GFA gain
amplifier under study.
- Still a lot of post processing / check to do for the
G(f).
5) Status of the work for the internal review on the LHC performance limitations during run I (on 25-26/09/2013) => All the speakers
- Beam-beam meeting last TH and LHC review meeting on Friday => Ongoing (preliminary):
- XB => Snow flakes and adjust instabilities => Most critical is really the ~ 1.5 sigmas.
- TP => Chroma changes from BB where the max change is at ~ 1.5 sigmas also and there is strong asymmetry between the 2 planes; asymmetry observed also for chroma contribution from octupoles sign change.
- DB => Lumi from experiments and separation all the fills, bunch by bunch he can see which bunch is blown up or not.
- NM => No sign of quadrupolar line at 1 – 2*Qy on the SBI signals analysed. Shape of the instability (after the onset) is different from the one at the end of the squeeze. Losses observed at the beginning of the trains.
- JB: Up-date on Sixtrack 6D beam-beam lens.
6) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (instability team): Answer to the idea / suggestion from Alexej Grudiev to try and increase transverse Landau damping in the LHC => Could an RF quadrupole be useful for this? This would introduce a linearly z-dependent transverse betatron tune (a nonlinear dependence could also be created by using higher frequency). For which kind of instabilities could this be useful? What are the required parameters to reach a transverse (incoherent) tune spread similar to the one from the Landau octupoles?
7) Miscellaneous
- Deadlines and important dates for ICE.
- The next (91st) meeting will take place on 04/09/2013 => Agenda:
1) Status of the work for the internal review on the LHC performance limitations during run I (on 25-26/09/2013) => All the speakers.
2) Brief reports of the 4 WGs (by the WG leader or replacement) => Plan, activities, deadlines, issues, etc.: BB, SC, EC, IMP.
- See preliminary agendas for the next meetings.
- See List of Actions.
Minutes by E. Metral, 28/08/2013.
