Minutes of the CCinS working group

2^nd meeting on Friday 20/11/2009 (11h00, 6/2/004)

Present: Rama Calaga (RC), Nicolas Delruelle (ND), Nicolas Gilbert (NG), Elias Metral (EM), Joachim Tuckmantel (JT),  Jorg Wenninger (JW) [Many thanks for coming despite the LHC start-up in the afternoon], Frank Zimmermann (FZ).

Excused: JT who might have been a bit late as he had another meeting at 10:00 (finally came almost at the beginning of the meeting).

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

1)  Comments of the previous (1st) meeting

 - NG sent an email to make a clarification concerning the "bumpers" which could be installed around the BBLR equipments: NG confirms that it has been requested to install 2 magnet "bumpers" type MDPV during the previous shutdown for the BBLR. However, due to lack of time, this request was delayed. Therefore, these 2 MDPV will certainly be installed during the next long shutdown, but this still has to be confirmed by J.P. Koutchouk => These clarifications have been added in the minutes of the 1st meeting.

2) Follow-up of the actions of the previous (1st) meeting:

- Action 1: JT will contact OB to discuss possibilities with klystrons (where can we found one as it seems KEK will not give us their klystron? Can we have the good frequency? If not, can we modify the frequency? By how much? etc.).

- Still to be done.

- JT contacted some colleagues from DESY (Dieter Proch, who is retired, and someone else) for a klystron around 500 MHz: " Hello, CERN is looking for a high power (100-200 kW, more would not harm) RF source around 500 MHz which we could use for a few weeks, maybe months in 2011/2012. Since DESY's main RF frequency is 499.xxx MHz, there might be a klystron 'available' (old or spare part) which CERN could borrow (and perhaps re-tune)? In any case CERN would pay for all efforts and guarantee a return of the borrowed equipment in perfect state as received; the upper management is very interested in this. Thanks a lot for your effort, Joachim Tckmantel, CERN-BE-RF (Background: The KEK crab cavity becomes 'available' when KEK-B stops
for upgrade work. At CERN there is a high interest to test such a cavity in a hadron machine (having no synchrotron radiation damping, ...) before committing the LHC upgrade on this path. This cavity could probably be detuned such that we could work at 508 ... 511 MHz where there is a harmonic number in the SPS allowing the required test conditions. KEK needs its present RF system elsewhere and we cannot hope to borrow it ..."

- Action 2: FZ&RC will contact KEK to check the figure of the speed for the dynamic tuning (1 kHz/s or 10 kHz/s?).

- FZ&RC sent an email to KEK and they are still waiting for the answers of actions 2-3-8-9-11.

- However, RC already confirmed that the speed for the dynamic tuning is 1 kHz/s.

- Action 3: FZ&RC will contact KEK to check the heat load (static + dynamic).

- Still waiting for clear answers from KEK, but meanwhile RC sent a talk by Nakai Hirotaka given at the 2007 MAC on the KEKB crab cavity cryogenics. Calorimetric measurements of the static heat loss of the cryostat and unloaded Q₀-factor of the crab cavity are discussed. The static loss for the HER crab cavity cryostat seems to be 32.25 W, while for the LER crab cavity cryostat it seems to be 25.73 W. The unloaded Q₀-factor of HER seems to be around 1E9 for the operating voltage of Vkick ~ 1.45 MV. The unloaded Q₀-factor of LER seems to be slightly larger. During this discussion, it was asked which crab cavity we will get from KEKB (HER or LER?). No answer yet (see Action 12 below).

- If we assume that the static heat load is the one deduced before, ND asked about the dynamic heat load. No answer yet.

- Action 4: ND will check which kind of refrigerators could be available (power capacity?, fixed or mobile? etc.).

- ND checked that the only refrigerator we have is the old one (installed in 1986) used by COLDEX in LSS4 called TCF20 (100 W, 4.4 K). It was also mentioned that we could reduce the dynamic loss by decreasing the field.

- ND thought another refrigerator of 400 W was available but it is not the case anymore as it was given to DESY few years ago.

- It can be moved from LSS4 to LSS5 but one needs to move the refrigerator + compressor + He storage vessel (+ ?) and a full maintenance is needed (as all these equipments were not used for some years) and it takes time (few months) and money (> 300 kCHF). Therefore, if possible it would be better to keep these equipments where they are (in LSS4) and install the crab cavity close to it.

- ND will show some slides about the LSS4 cryogenics installation during the next (3rd) meeting (see Action 13 below).

- Action 5: NG will start checking where 5 m of equipments could be installed (with a distance between beam and outside dimensions of ~ 0.5 - 1 m).

- NG sent a cross-section of the SPS to show that, as he mentioned during the 1st meeting, the maximum distance between the centre of the beam and the maximum outside dimension of the equipments we want to install has to be smaller than 580 mm (at least on one side, as it could be asymmetric and there is more space on the other side) otherwise there will be problems with the transport.

- NG presented some slides to discuss possible locations in LSS4 or LSS5: Coldex, LSS4-, LSS4+ and LSS5.

- It was reminded that the LHC prototype collimator installed in the SPS since 2004 (TCSP.51934) will be replaced by a new one with buttons inside. Furthermore, it is also planned to install a second LHC prototype rotatable collimator from SLAC.

- NG told us that the only possibility in LSS5 is in 516 (LSS5), in front of the access tunnel (2 pieces of vacuum chamber in 51661 and 51691). The advantage is that there is a mini cavern (for the cryogenics) few meters from there.

- In LSS4, there are 2 pieces of vacuum chamber (41760 and 41779) after COLDEX (LSS4+), in 417, but JW reminded us that it is in the middle of the extraction bump (for extraction towards LHC and CNGS) and therefore the horizontal orbit would be quite large. The maximum (~ 32 mm) of the extraction bump is in 418, corresponding to the BPH number 68 called BPCE.41801 (Picture 1, 2, 3 and 4). This bump is made with 3 bumpers: MPLH4165, MPLH4199 and MPSH4219 (Picture 5). In the proposed location (417), the horizontal orbit would be ~ 10 mm. Furthermore, this extraction area is also radioactive and it will not be easy for accesses. This could be a showstopper not to install the crab cavity there.

- Another possibility could be COLDEX in 41737 (if we can remove it => See Action 14 below). It is just before the location discussed before, it is still in the extraction bump (at the start of the bump), but the horizontal orbit would be slightly smaller, which is better. Furthermore, there would be more space and the cryogenics equipments already there. Therefore, it is a very attractive location.

- NG found also a location just before the kicker, in 41439 (LSS4-). There is ~ 6 m, it is not in the extraction bump (therefore it seems ideal!) but here we are quite far (~ 15-20 m) from the cryogenics (in the middle of the tunnel) and the limit of 580 mm will have to be respected. Reminder: the longer the transfer line the longer the heat loss but it is not a fundamental issue at this stage as we could possibility buy and install a new transfer line (for the cryogenics).

- Action 6: EM (with NG and ND) will contact Miguel Jimenez and Giovanna Vandoni (Vacuum) to check what the status with the old experiment COLDEX in LSS4 is and see if we could remove it and install the crab cavity. In fact Giovanna could also make a summary at one of the next meetings.

- EM sent an email to Miguel Jimenez and Giovanna Vandoni: " Dear Miguel and Giovanna, In the frame of the CCinS working group, we want to check what the status with the old experiment COLDEX in LSS4 is and see whether we could remove it and install the crab cavity there (if needed). Could you please tell me (us) what your plans with it are? May be Giovanna could make a short report on it at the next (or at the one after the next) meeting. In summary, we are looking for a length of 5 m, close to some cryogenics equipments".

- GV answered that she "will discuss this with Miguel and Vincent. As you propose, I may present the logistics and implications in a report to the WG on the crab cavity" (see Action 14 below).

- Action 7: EM&NG&ND (and any other people) would like to go and visit LSS5 and LSS4 (in particular COLDEX) => NG will add us in the SPS access requests. We could do this access in case of SPS stop or after December 16th (i.e. on 17/12/09 or 18/12/09). 

- NG mentioned that an access is foreseen in the SPS to visit LSS4 and LSS5 on Tuesday 24/11/09 in the afternoon.

- Action 8: RC will send all the crab cavity impedance data to Elias.

- Still waiting for answer from KEK.

- Action 9: RC&FZ will contact KEK to have a description of all the feedbacks used with a crab cavity operation. 

- Still waiting for answer from KEK.

- Action 10: EM will contact FC to check if the Schottky monitor can still be used.

- It was reminded that this diagnostics could be used to study the noise, which is an important concern.

- EM contacted Fritz Caspers, Rhodri Jones, Elena Shaposhnikova and Thomas Bohl. The answers are the following:

- Fritz and Rhodri Jones told EM that the Schottky monitor (in SPS BA5) had to be taken out and was given to BNL about 5 years ago. It is now in RHIC, doing a very good job.

- Elena told me that the best person to ask about Schottky diagnostics in the SPS is Thomas Bohl and that she seemed to remember that there is still one in the SPS for transverse measurements (in BA2?). This was indeed confirmed by Thomas that some equipment (kicker, PU, cables) is still available in the SPS for transverse Schottky measurements. What is missing - control of device on the surface. To bring it back even to the old state a serious consolidation work will be needed.

- I asked Thomas that what I would like to know is: Do we have Schottky monitors? (longitudinal and transverse?, how many?, In which positions in the SPS are they?, Do they work? If not, what shall be done to make them work? How much will this cost? etc.). I am waiting for his answers.

- Action 11: RC&FZ will provide a detailed list of what we want to measure (precisely) and how, with (if possible) numbers and pictures without and with the effect of the crab cavity (for instance coming from KEK measurements).

- RC&FZ said that we will do a commissioning of the crab cavity, beam set-up, scan of the RF phase (+- 180 deg), impedance measurements, tune shifts measurements, scans introducing some noise (modulation of phase), etc.

- FZ said that we have to show that we do not blow up the beam with nonlinearities.

- FZ said that it was already discussed during the 1st meeting but EM replied that it was a bit vague and that more precise measurements (with rough estimates of the order of magnitudes etc.) would be highly desirable. RC suggested that we write (with FZ and EM) a small document for the next (3rd) meeting.

- EM asked if we need for instance to install a streak camera to be able to make such measurements (as it is done in KEKB). However, a streak camera needs synchrotron radiation, which is much smaller in the SPS (hadrons machine) than in KEKB (leptons machine). Therefore, this cannot be used. One needs instead a (working) HEADTAIL monitor.

- RC said that except the measurements with the streak camera, one should be able to redo all the measurements performed in KEKB.

- JT reminded us that one should measure first all the things one wants to measure before the crab cavity is installed, and then after, to be able to make a meaningful comparison. 

3) Other discussions:

- Discussion with Karel Cornelis outside the meeting: One of the most important measurements is the study of the beam lifetime in coast with some spread and also perhaps the BBLR ON.

- Jorg asked whether when the crab cavity is OFF (the cavity has to be passive) one can allow orbits of ~ 5-10 mm, as the SPS orbit is quite large. FZ reminded us that the impedance of the crab cavity is very small and could not be measured by KEKB. Furthermore, the crab cavity could also be warm. RC reminded us that the idea would be to detune the crab cavity and have active feedbacks. JT said that we detune the crab cavity to stay between 2 lines of the revolution frequency (which is 43 kHz). The effect of the detuning could be checked by simulation (RC, see Action 15 below).

- Jorg asked what is the maximum kick voltage we can have. FZ replied that the integrated maximum value is ~ 2 MV (it was designed for this value).

- FZ asked if there was any preference from RF. JT replied that if we have a klystron of ~ 400 kW, one might  need ~ 1 MW of power. The question is: where do we have this power? JW reminded us that point 4 is a critical point electrically. NG will follow this up (see Action 16 below).

- FZ asked how we could check the failure mode. JT said that he can compute quite precisely what could happen (JT will present his analyses on few slides during the next 3rd meeting, see Action 17 below). JT said that we need the feedbacks for the impedance: the power limit the maximum orbit deviation one can have, while the gain is for the beam stability. JW said that one should attack this issue from 2 sides: (i) by measurements with beam, (2) by bench measurements on a cavity. RC reminded us that the situation of an RF phase shift of 180 deg never happened in KEKB.

- Jorg reminded us that one needs to separate beam quality and machine protection: if the worst effect is not dangerous then we have to look at the beam quality (is there some blow-up?). 

- JT said that one needs a cooling if 1 (HOM) mode is drived as there will be heating. For this matter, a cold cavity is preferred compared to a warm one.

- NG said that if we have He in the tunnel, we need the same system of protection as in the LHC (=> ODH = Oxygen Deficiency Hazard, some info). NG will follow it up (see Action 18 below). For this, NG needs the total amount of He underground. After the meeting, RC said that he will ask the KEK people. Naively he would say ~ 50 l, but one needs a confirmation from KEKB (RC is waiting for it). NG checked after the meeting the SPS ventilation and found that the air is not extracted in point 4 but it is injected there, which does not go in the good direction for us. Therefore LSS5 is better than LSS4 in this respect.

- RC reminded us about the 2 possible schemes with crab cavities: local vs. global compensation.

- Local compensation: An ideal crab scheme would involve a local compensation with two cavities on either side of the IP, leaving the closed orbit in the rest of the ring unchanged.

- Global compensation: For the case with two IPs, two cavities are sufficient to satisfy the phase advance constraint to achieve head-on collisions at both IPs. However, an oscillating closed orbit for particles away from the center of the bunch, although not catastrophic, can pose aperture and tune shift constraints that will limit the crossing angle. In addition, the motion of particles in the bunch head and bunch tail will become more sensitive to the magnetic errors in the entire ring.

- NG asked about the RP impact, i.e. will the place where the crab cavity will be installed become hot? Jorg replied that it will not be more than now without the crab cavity. It should not be a place of losses. In fact, we should even aim at a place of minimum of losses to install the crab cavity. This could go in favour of LSS5 or LSS4 but before the extraction kickers.

- JT said that there should be nobody close to the crab cavity when it is ON. Therefore, it should may be linked to the interlocked chain 1, as suggested by NG. RC said that one should follow the similar procedures as with the main RF (there will be some X-rays etc.).

- Jorg reminded us that there is no sectorization in the SPS (contrary to the case of the LHC) yet.

- FZ asked whether we could modify the COLDEX experiment to be able to move the crab cavity (which would be then much easier from the operation point of view). The answer will certainly come from GV when she will summarize the status of the COLDEX experiment at the next (3rd) meeting.

4) Actions to be taken for the next meeting

- Action 1 (from 1st meeting): JT will contact OB to discuss possibilities with klystrons (where can we found one as it seems KEK will not give us their klystron? Can we have the good frequency? If not, can we modify the frequency? By how much? etc.).

- Action 2 (from 1st meeting): FZ&RC will contact KEK to check the figure of the speed for the dynamic tuning (1 kHz/s or 10 kHz/s?). DONE.

- Action 3 (from 1st meeting): FZ&RC will contact KEK to check the heat load (static + dynamic).

- Action 4 (from 1st meeting): ND will check which kind of refrigerators could be available (power capacity?, fixed or mobile? etc.). DONE.

- Action 5 (from 1st meeting): NG will start checking where 5 m of equipments could be installed (with a distance between beam and outside dimensions of ~ 0.5 - 1 m). DONE.

- Action 6 (from 1st meeting): EM (with NG and ND) will contact Miguel Jimenez and Giovanna Vandoni (Vacuum) to check what the status with the old experiment COLDEX in LSS4 is and see if we could remove it and install the crab cavity. In fact Giovanna could also make a summary at one of the next meetings. DONE.

- Action 7 (from 1st meeting): EM&NG&ND (and any other people) would like to go and visit LSS5 and LSS4 (in particular COLDEX) => NG will add us in the SPS access requests. We could do this access in case of SPS stop or after December 16th (i.e. on 17/12/09 or 18/12/09). DONE.

- Action 8 (from 1st meeting): RC will send all the crab cavity impedance data to Elias.

- Action 9 (from 1st meeting): RC&FZ will contact KEK to have a description of all the feedbacks used with a crab cavity operation. 

- Action 10 (from 1st meeting): EM will contact FC to check if the Schottky monitor can still be used. DONE. (still waiting for final answers by Thomas Bohl).

- Action 11 (from 1st meeting): RC&FZ will provide a detailed list of what we want to measure (precisely) and how, with (if possible) numbers and pictures without and with the effect of the crab cavity (for instance coming from KEK measurements).

- Action 12: RC&FZ will contact KEK to check which cavity (HER or LER) could come to CERN.

- Action13: ND will show some slides about the LSS4 cryogenics installation during the next (3rd) meeting.

- Action14: GV will make a presentation about the old COLDEX experiment (and the possibility to install a crab cavity instead) during the next (3rd) meeting.

- Action 15: ? will check the effect of the crab cavity detuning by simulation.

- Action 16: NG will check where we have ~ 1 MW of power available in the SPS.

- Action 17: JT will present his analyses of possible failures on few slides during the next (3rd) meeting.

- Action 18: NG will follow the ODH issue. For this, RC will contact KEK to have the total amount of He underground.

5)  Miscellaneous

- Next meeting on Friday 27/11/09 between 11:00 and 13:00 (max), in room 6/2/004.

Minutes by E. Metral, 23/11/09