Minutes April 17th, 2008
Present: Gianluigi Arduini, Rama Calaga, Fritz Caspers, Elias Métral, Federico Roncarolo, Giovanni Rumolo, Benoit Salvant, Elena Shaposhnikova.
Agenda
- Benoit Salvant
"HeadTail simulations of SPS bunch with the kickers" (slides, minutes)
and
"SPS impedance webpage" (minutes)
- Rama Calaga
- AOB (minutes)
Minutes (taken by Elias --> Many thanks!)
Email sent by Elias Métral for the invitation (to Gianluigi Arduini; Benoit Salvant; Giovanni Rumolo; Rama Buchi Rao Calaga; Elena Chapochnikova; Fritz Caspers; Federico Roncarolo on 09/04/08):
“Dear colleagues, I would like to invite you to our 2nd SPS impedance informal meeting on 17/04 in room 6/2-004 from 14:00 to 16:00, where one will discuss:
1) Localization of the transverse impedance in the SPS and RHIC by Rama.
2) Status of the SPS impedance web page by Benoit.
3) Status of Bruno Spataro's simulations by Elias.
4) Where we stand in the actions (mainly for Benoit and I) below (from the previous meeting).
Please tell me if you would like to discuss other items.
Cheers,
Elias.
PS: I remind you below the actions (mainly for Benoit and I) of the last minutes (meeting held on 05/03/08):
1) Continue the comparison between parabolic and Gaussian bunches for Sacherer’s formula (mode 0 only) => Effective and real impedance.
2) Produce a table of effective impedance deduced from Helmut’s measurements over the year (Gaussian bunch, Parabolic bunch and HEADTAIL simulation).
3) Simulate the TMCI with the MKE kickers only (with the real wakefield) => Was done already in the past by Giovanni to see the threshold. Now one wants to look at the evolution of the different modes, which modes are coupling etc., and what is missing to explain the measurements.
4) Start HEADTAIL simulation for the longitudinal plane => Quadrupolar oscillation vs. intensity with a broad-band impedance first and then we will use the wakefield that we already have.
At the last meeting, there was also a question from Elena, who wants to know the way the incoherent band is shifting with intensity when emittance Blow up is made with some band limited noise (double RF bucket in SPS and single RF bucket in the LHC). After discussion with Gianluigi and Giovanni it is believed that Giulia Papotti could perhaps perform this study with HEADTAIL => To be discussed at the next meeting”.
Comment before the meeting by Fritz (09/04/08):
“We should make sure that there are no bad surprises in the SPS from kicker heating related trouble [outgassing , going beyond the Curie point] (like we had it in 2004) in particular when we have to run full blast to fill the LHC (and the beam is lost or dumped in the LHC thus requesting frequent refills).”
Elias sent an email to Laurent Ducimetiere today (on 17/04/08) to ask him some more info about the heating reduction with the shielded kicker etc.
Action 1:
Elias will send the answer (when it comes) to everybody to see if one
can run all the nominal operational beams (nominal LHC but also FT, CNGS
etc.). Elena also mentioned that there will be a presentation at the SPS
upgrade meeting on 13/05 to see the limitations from the SPS kickers
heating etc. for upgrade scenarios.
Action 2: Benoit and
Elias will try and solve this possible discrepancy as well as the issue
of Parabolic/Gaussian distribution to make a consistent data analysis.
- Suggestions for MDs in 2008: (i) Take data for different bunch lengths, and (ii) Take data at a different energies (26 and 37 GeV/c and MD cycle available in the supercycle or higher, if needed. This should allow measuring the detuning with intensity and phase advance vs. intensity for different bunch length – by varying the RF voltage – and get some possible information on the frequency spectrum of the impedance).
Action 3: Rama will
perform HEADTAIL simulations to try and understand what happens starting
with the simplified case of a single localized impedance, looking at the
horizontal and vertical planes for a round and flat structure etc. On
the basis of these results the type of constraint to be imposed will be
defined and the analysis of the data should be done. Rama will ask Frank
Zimmermann whether he has the 2003 data and/or whether he can redo the
analysis with the constraints that will be defined so to have a
comparison of the measurements in different years.
- In some analyses Rama has a peak exactly at an electro-static septum. Gianluigi mentioned the current simulations from Bruno Spataro on the electro-static septum (only the tank for the moment!). However, equivalent septa (also in numbers) were in point 6 in the past, and no huge effects were observed when they were removed during the 2004 and 2006 long shutdown.
- Elena mentioned that the single-bunch longitudinal instability threshold is again closed to the transverse one (without 800 MHz and at 26 GeV/c). This will be studied in detail by Benoit as it is part of his PhD thesis.
Action 4: Benoit will study the longitudinal plane in the same way as the transverse one taking the “real impedance” instead of a Broad-Band impedance model, starting with the wake-field from all the kickers. The situations in 2007 should be taken – i.e. with MKQH shielded and the “shielded” MKE kickers (up to now these shieldings were not taken into account).
- Fritz reminded us also to keep an eye on the coherent spectrum above 1.5-2 GHz.
- Finally, concerning last meeting's request from Elena (study the way the incoherent band is shifting with intensity when emittance blow up is made), Elias proposed (after discussions with Gianluigi and Giovanni) that Giulia Papotti could maybe perform this study. Elena replied that Giulia has some other commitments and that she will certainly not be able to perform it. Elias said that Benoit is also in the same situation.
Action 5: Gianluigi and Elena will try and find someone to perform this study.
Author: Benoit Salvant CERN
AB/ABP-LIS