Minutes of the CCinS working group

4^th meeting on Thursday 10/12/2009 (14h00, 6/2/004)

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

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

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

1)  Comments of the previous (3rd) meeting

 - 2 clarifications:

- 110 W for liquid N2 at 80 K correspond to only few W at 4.4 K. Therefore, the contribution to the heat load is negligible.

- If 2 IOTs are needed (to have ~ 160 kW of RF power), it will cost ~ 800 kCHF. Adding the electrical power requests from RF (~ 320 kW) and cryogenics (120 kW), an electrical power of at least ~ 440 kW is needed.

2) Follow-up of the actions of the previous (3rd) meeting:

- EM mentioned that he had several discussions with JT and Gianluigi Arduini on the possibility or not to use the bypass. EM mentioned that he sent an email to ND to ask him more information about the way we could use the bypass, i.e. move the Crab Cavity in the beam for MDs and put it back out for physics (how was it done with COLDEX?). Possible issues could be: Can we move a cold box when it is cold or do we need to warm it up first? Do we have flexible transfer lines which allow to move the Crab Cavity by ~ 1 m? etc. ND answered that we can move the Crab Cavity when it is cold (we do not need to warm it up) but we need first to empty it. Concerning the flexible transfer lines, they were used (and worked well) for COLDEX. Therefore, ~ 1 week before an MD we could have it cold (still outside the beam, injecting He gas to cool it down to 4.4 K and keep it empty, i.e. with no liquid). Then, when we want to have the MD, we move it inside the beam and fill it (~ 400 l in total) by putting liquid He => Should take ~ 1 complete day (with the stabilization). Therefore, the 1st day of a 3-day MD block could devoted to this and the MD proper could start the 2nd day (Note that during the time the cavity is filled, another MD could take place if the Crab Cavity does not perturb...). After the MD, we would then have first to evaporate the He (~ few hours) and then move it back out of the beam.

- RC asked if we could put a bellows on a waveguide (even if a frequency of 500 MHz means large size etc. ). It seems that the best would be to move the cavity in the beam and then take few minutes (in local) to attach (screw?) the waveguide and allow RF power to be injected in the Crab Cavity.

- EM said that he will meet Tobias Dobers (BE/ABP/SU) after this meeting to look at the possible integration of the Crab Cavity at the location of COLDEX.

- RC sent us more drawings (byonet drawings of the LHe and LN2) from the KEKB Crab Cavity (byoKF50-flow.dwg and byoKF50-return.dwg) for ND, i.e. for the cryogenics ports.

- JT mentioned that there is still one point to be elucidated for the RF power: "Long ago we had a single tetrode for a 400 MHz sc. cavity working there but we should check that there is room enough for 1, perhaps 2, amplifier(s) with power-supply. Each unit needs 2x2.5 m footprint and 2.5 m height, best in an area that is not directly 'sprayed' by the beam. On request Eric Montesinos thinks that maybe – needs study – one could put the power-supplies on the surface (... somewhere ...) but one would still need about 1x1 m footprint per amplifier 'close' to the cavity". NG mentioned by email that the "surface solution" might be necessary as a height of 2.5 m will certainly be a problem for the SPS "monte-charges". A possibility could be, perhaps, to use a crane via the BA4.

- NG and Simon Baird informed EM that NG will not be able to continue to participate to the CCinS working group (shutdown activities until ~ February 2010).

- RC mentioned that we could ask the KEK people to increase the Qext (when they will modify the frequency from 509 to 511 MHz) because they have a shorter coupler.

- Reminder: Operationally one prefers to have a low Qext, as in this case we are less sensitive to perturbations. But, from the Machine Protection point of view, one prefers to have a high Qext, as in case of problem the Crab Cavity reacts more slowly. In this case we can leave with less power but we are more sensitive to vibrations (phase changes etc.) and offset => Huge transverse impedance!

- Concerning the Machine Protection, EM discussed with JW after this meeting and it was agreed that the SPS should be used to make only observations, i.e. one should not make interlocks for the SPS. 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.

- NG followed up the ODH issue with Karl Gunnar Lindell (see email).

3) Rama's Talk on possible SPS measurements with a Crab Cavity and answers from KEK

- Rama started first to try and summarize the main figures for the Crab Cavity:

- Length = 5.081 m.

- Weight = 5830.5 kg.

- Height from ground to beam = 1.50 m (reminder: it has to be 1.20 m in the SPS). A possibility is to remove to bottom part of ~ 0.5 m and replace it by a system of rails (with motorization etc.) within a height of ~ 20 cm (still to be checked if this is feasible).

- Total height ~ 3 m. Reducing it as mentionned before by ~ 30 cm, the height will become ~ 2.70 m (which is still higher than the SPS ceiling of ~ 2.35 m). However, in the upper part there are mainly thin tubes (see picture of the HER Crab Cavity).

- On the second slide, GHe means Gaseous Helium. It can be seen that there is the LHe Inlet (we inject LHe) and the GHe out (the gas which goes out), as expected, but ND asked what "LHe out" is for? ND said that he has enough information at this stage of the project, but he would need more in the future (RC reminded ND to have a look also to the talk by Nakai discussed at the 1st meeting).

- On the 3rd slide, RC summarized the preliminary RF & Cryo specifications. The 400 l (volume of the He vessel) seems to be the total volume, but we won't fill the whole volume: at the end, it will be ~ 200 l of liquid and ~ 200 l of gas.

- On the 4th slide, the longitudinal position of COLDEX is mentioned together with the Twiss parameters at this location (which have to be checked, as there are quite different from the ones discussed during the 5th meeting: see request from the CCinS working group). However, these are only first estimates. RC succeeded to insert a Crab Cavity at this location in MAD and to make first simulations. He compared these first results with the ones obtained from the linearized formula. Orbit shifts (due to the Crab Cavity kick) of ~ 0.5 - 1 mm are predicted at 120 GeV/c with 1.5 MV. However, as the real bunch in the SPS should quite long with respect to the RF wavelength, the exact formula should be preferred (see 5th meeting: request from the CCinS working group). Ideally one would prefer to have zero horizontal dispersion, which is not exactly the case here but it is still relatively small. Interesting effects could even be studied.

- On the 7th slide, more items are discussed:

- Impedance (longitudinal and horizontal) spectra => Some data were sent to RC after the meeting: scratch.ReZ_AT_XY.0001.txt, scratch.ImZ_AT_XY.0001.txt, scratch.ReZx_AT_XY.0001.txt, scratch.ImZx_AT_XY.0001.txt.

- Should we take the HER or LER Crab Cavity? It was said that we should use the high-voltage and high-trip rate Crab Cavity and operate it at lower voltage.

- The Crab Cavity commissioning (step 1) is discussed on slide 8.

- The first thing to check is the beam survival (BCT > 1 turn!).

- RC reminded us that the SPS BPM resolution is not very good below ~ 1E10 p/b.

- The instrumentation is discussed on slide 9.

- On the next slides, RC showed some experiments made in KEKB with electrons.

- The accumulation of beam with Crab Cavity ON at 0 V but with a feedback ON to fight offset beams.

- An RF noise experiment reveals that away from the betatron line no transverse emittance growth is observed. However, we moving closer to it, the emittance increases.

- Experiments on beam-beam effects and on crab dispersion were also performed.

- RC finished his presentation, by summarizing the SPS tests objectives with protons.

- FZ suggested to prioritize the subjects to be studied in the SPS:

1) The study of the horizontal emittance lifetime (without and with Crab Cavity) is the first and most important item (i.e. the study of the effect of the RF noise on the horizontal emittance). JT reminded us that if we double the kick we double the noise. We could also inject a large RF noise and observe how the horizontal emittance grows, which should help us to define the RF noise limit.

2) Impedance effects with horizontal orbit control.

3) Estimate the diffusion rate with the scraper and collimators (or with some UA9 detectors, such as MEDIPIX etc.).

4) Study of the Machine Protection and reliability issues: increase the Crab Cavity voltage and study the scaling of the trip rate with RF voltage. Scan the synchronous phase, and the horizontal beam offset.

5) Collimation issues: EM mentioned that in the future there should be 2 collimators in the SPS (1 from CERN, as it is the case since 2004, and 1 from SLAC, which should come in 2010 or 2011). FZ mentioned then that it could be very interesting to study the effect of the crab cavity on the collimation system (and check if a primary collimator could become secondary etc.). After this meeting, EM followed this up and the CCinS working group made a request for the installation of the 2 SPS collimators, to have the correct phases advances (see 5th 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.). DONE (in fact JT follows this as OB has no time).

- 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). DONE.

- 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. DONE.

- 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) => RC will make a presentation at the 4th meeting. PARTIALLY DONE.

- 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 => ND could not do it as he could not go in the SPS tunnel (no access rights).

- 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. DONE.

- 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. DONE.

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

- Action 19: RC will make a presentation at the next (4th)  meeting where he will summarize all the info he got from KEK and where he will present the possible measurements in the SPS (with some orders of magnitude). PARTIALLY DONE (see Action 11 above).

- Action 20: EM will contact the Survey People (e.g. Christophe Podevin) asap to have a precise idea of the whole area around COLDEX. This could be translated in a small mockup. According to NG, the Survey People would need ~ 1/2 day in the SPS. DONE (EM is following this with Tobias Dobbers).

5)  Miscellaneous

- Next (5th) meeting on Wednesday 16/12/09 between 09:00 and 12:00 (max), in room 6/2/004.

Minutes by E. Metral, 18/12/09