Minutes of the CCinS working group

5^th meeting on Wednesday 16/12/2009 (09h00, 6/2/004)

Present: Nicolas Delruelle (ND), Elias Metral (EM), Joachim Tuckmantel (JT), Frank Zimmermann (FZ).

Excused: Rama Calaga (RC), Nicolas Gilbert (NG), Jorg Wenninger (JW).

Absent: Olivier Brunner (OB), Giovanna Vandoni (GV).

1)  Comments of the previous (4th) meeting

 - None.

2) This meeting was devoted to prepare our answer(s) to the management

- No real showstoppers were identified. However, many issues remain to be studied in detail. The crab cavity will be used in KEKB until June 2010 (at the earliest) or end of the year 2010 (at the latest). Knowing that it will then have to be removed from the tunnel, modified to have the frequency of 511 MHz etc., we believe that the crab cavity could be used/tested in the SPS only in 2012.

- The best location for the KEKB Crab Cavity is the location of COLDEX.41737, which is not used anymore and which can be removed. The 2 main reasons are the space (a cavern is required) and the available cryogenics.

- EM mentioned that he met Tobias Dobers (for the integration), who recently made a seminar on laser scanning at CERN. The idea is to have with this method a cloud of points of the region of COLDEX: the instrument takes 2000 point/s in 3 D and with a precision of 6 mm over a distance of 60 m; a software is delivered with the scanner, which enables the 3D navigation and which is called Cyclone. Then we could make a mesh with CATIA (Yvan Muttoni), removing the points from COLDEX, and if we have the CATIA model of the CC we could see if we have integration interferences or not. I asked him to have +- 5 m from the centre of COLDEX. This could be done in ~ 1/2 day. However, Tobias checked that he already scanned this area (see laser scanning picture of COLDEX area by Tobias). However, a part of it is missing (behind the COLDEX experiment) and Tobias will do it on 21/01/2010 (already planned with Nicolas Gilbert).

- As collimation could be an issue with crab cavities and as a 2nd collimator (from SLAC) should be installed in the SPS (in 2010 or 2011), the best location of the SLAC collimator was studied and a request from the CCinS working group was made (after the meeting, on 17/12/09). Note that the Crab Cavity is horizontal and the 2 collimators are also horizontal. With the proposition, the phase advances are such that almost no crab effect is seen at the 1st (SLAC) collimator, whereas the full crab effect is seen at the second (CERN) collimator. However, to do so the vertical Ionization Profile Monitor needs to be moved before the QD.517 (the relevant people were informed: Nicolas Gilbert contacted Gerard Tranquille). Pictures of the area around QD517 were taken by Oliver Aberle on 18-12-2009: 1 and 2.

- A first time estimate to remove COLDEX is ~ 2-3 weeks.

- A first estimate to change the PLC and for the supervision of the old cryogenics system (TCF20) is ~ 200 kCHF.

- Concerning the IOT(s), Eric Montesinos could buy the 1 or 2 that we would need (1 might be enough if Qext is high enough) together with the IOTs he will buy to replace the SPS klystrons (the cost of 1 is ~ 400 kCHF). We have to tell him asap. Another issue is the space needed.

- As the Crab Cavity will come from Japan after a long trip and some modifications, it would be wise first to test it somewhere at CERN (SM18?) before installing it in the SPS. The cryogenics should be already there (at SM18) but an amplifier would be needed (may be the same as the one we will use in the SPS). However, it could be that there is no much space there (to be checked).

- Concerning the measurements in the SPS, it was agreed that one of the most important ones is the effect of the RF noise. To study this, one needs first to have a beam with good "horizontal emittance lifetime" (and not only the usual beam lifetime) of may be few 10s of h. Furthermore, the tilt from the CC should be at least of the order of the horizontal beam size to see something (which would ideally mean to use bunches with a horizontal rms. norm. emittance of 2 microm and a beam momentum of 55 GeV/c => See request from the CCinS working group). Therefore it is proposed to perform some MDs in 2010 in the SPS to study the horizontal emittance lifetime in coast (at 55 or 120 GeV/c) with few bunches (first, and then few batches to challenge the RF, introducing transients) spaced  by 4 25 = 100 ns (to be more precise 4 24.95 = 99.8 ns which is compatible with a frequency of the Crab Cavity of 511 MHz). The good news is that the 100 ns bunch spacing beam will be prepared next year to satisfy a request from ALICE. Note that beams with 25 ns and 50 ns could also be used, but in this case, some bunches would be crabbed and others not, which could in fact be used to study the phase stability.

- Concerning the new CERN collimator which will be installed for 2010 (with integrated BPMs), it was asked if we could measure bunch by bunch. This has to be checked as this could be very interesting.

- Concerning the Machine Protection, it was agreed that the SPS should be used to make only observations, but one should not make interlocks. In principle, there could be in fact 2 kinds of interlocks: slow (on BPMs) and fast (on RF). One might have in 2011 a BPM interlock post-mortem, i.e. the last 1000 turns, to study what happened, but the resolution is not so good. Ideally, we would need to put a fast RF interlock. What could be studied is the effect of the Qext to see if the phase cannot go rapidly wrong etc. However, it seems that we will not be able to play with the Qext as it is fixed for KEK. A new design would be required to have different Qext.

- Concerning the SPS availability for the other high-intensity beams, it is proposed to use a bypass (as was used in the past with COLDEX). We could even imagine to leave the Crab Cavity in the physics beams if there is no problem, but in this case we need to keep the cavity cold, which will require a piquet etc. Therefore, this does not seem feasible. The issue is to study in detail the motorization to move the Crab Cavity (~ 5 tons, compared to ~ 0.5 ton for COLDEX).

Minutes by E. Metral, 18/12/09