Minutes of the ICE section

9th meeting on Wednesday 22/09/2010 (08:40-10:30, 6/2-004)

ICE members: Benoit Salvant (BS), Christian Hansen (CH), Carlo Zannini (CZ), Diego Quatraro (DQ), Hugo Alistair Day (HD), Elena Benedetto (EB), Ewen Hamish Maclean (EHM), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Rumolo (GR), Jean-Luc Nougaret (JLN), Kevin Shing Bruce Li (KL), Maria Carmen Alabau Pons (MCAP), Nicolo Biancacci (NB), Nicolas Mounet (NM), Olav Ejner Berrig (OB), Tatiana Pieloni (TP), Werner Herr (WH).

Present/Excused: BS, CH, CZ, DQ, HD, EB, EHM, EM, EW, FS, GR, JLN, KL, MCAP, NB, NM, OB, TP, WH, Fritz Caspers, Eirini Koukovini Platia, Torsten Weber, Frank Zimmermann.

1) Newcomers / visitors

- None.

2) Comments on the minutes of the 8th meeting + Actions

- No particular comment from anyone.

- List of Actions.

3) General infos

- No particular comment from anyone.

- SL meeting last week:

- DG presented a new schedule, with a 4 week ion run in every operational year.

- Fermilab has the right to run the Tevatron for 3 years (but the DOE does not give any funds).

- 3 global projects will be made in the BTE sector:
    1) Consolidation S. Baird  (EN)
    2) High Luminosity L. Rossi  (TE)
    3) Injector Upgrade R. Garoby  (BE)
    These people will be deputy department leaders. All projects would then be under one of these umbrellas.
    This also means that Oliver will step down as deputy BE leader.

- Follow-up of the situation with the IR3MBC collimators: EM (in the absence of BS) presented the recent results obtained by BS from HEADTAIL simulations showing that the situation gets even worse when increasing the chromaticity from 0 to 2 or 4 (in Qprime units). The next step will be to include octupoles and see if this instability can be stabilized (Action1: BS and NM).

- Reminder from Ralph Assmann (discussion after the meeting): The goal with IR3MBC was not to increase the performance (hopefully not decrease it as well) but the main motivation behind was the "single-event upset" (A single event upset (SEU) is a change of state caused by ions or electro-magnetic radiation striking a sensitive node in a micro-electronic device, such as in a microprocessor, semiconductor memory, or power transistors). The situation with the electronics in IR7 is more critical than in IR3 and we should gain a factor 100 by moving to IR3.

- Information from Miguel Jimenez: ALL SPS BPMs are isolated by enamel flanges (one in each side) and an additional layer of vetronite. In the procedure, it is clearly written that these flanges shall stay isolated (electrically tested by Vacuum Crews) after assembly. Furthermore, RF bridges were never installed in the SPS.

4) Review of the Beta-Beams activity (EW): ppt

- Reminder: The aim is to produce (anti-)neutrino beams from the beta decay of radio-active ions circulating in a storage ring with long straight sections (Zuchelli, 2002 => He is not at CERN anymore and it seems he now works in a private company).

- Reminder on the 3 unknown neutrino oscillation parameters: θ₁₃ , δ_cp and Sign(Δm₃₁²).

- Energy of the neutrinos:

- Reaction energy Q typically of a few MeV,

- Accelerate ions to relativistic γ,

- Boosted neutrino energy spectrum: E_ν ≤ 2γQ,

- Forward focusing of neutrinos: θ ≤ 1/γ,

- 2 different parent isotopes to produce ν and anti-ν respectively.

- Choice of radioactive ions species:

- Optimum lifetime given by the acceleration scenario: In the order of a second.

- Low Z preferred:

- Minimize ratio of accelerated mass/charges per neutrino produced

- One ion produces one neutrino

- Reduces space charge problems

- 6He and 18Ne.

- 8Li and 8B.

- There are a high-energy and a low-energy beta beam study => We concentrate here on the high-energy design.

- There are 2 projects funded by Europe:

- Eurisol design Study, EC FP6, 2005-2009 (which still continue):

 - 6He and 18Ne (there is an error in the slides: it is 18Ne instead of 19Ne mentioned in the slides), ISOL

- Baseline: Frejus

- Gamma: 100, Low-Q ~ 3.5 MeV

- 18Ne production, ISOL, 20 times below requirements (from a top-down approach) => 18Ne isotopes seemed to be not possible to produce with ISOL technology: New Ideas were needed => The new ion production approach is the basis for the 2nd project (see below the new proposal). However, since then a new proposition seems to work on paper and therefore this option is still studied in // to the new one.

- No beam stability studies

- Decay Ring RF HW not studied

- Low energy part of acceleration not studied

- EUROnu Project, EC FP7, 2008-2012 (may be prolonged):

- 8Li and 8B (supposed to be easier to produce), Production Ring, Ion collection => New approaches for the ion production:

- Beam cooling with ionisation losses C. Rubbia, A Ferrari, Y. Kadi and V. Vlachoudis in NIM A 568 (2006) 475487.

- Development of FFAG accelerators and their applications for intense secondary particle production, Y. Mori, NIM A562(2006)591.

- Baseline: Canfranc / Gran Sasso

- Gamma: 100, High-Q ~ 16 MeV

- 18Ne production intensified, experiments for 6He

- Low energy part of acceleration studied

- Intense beam stability studied (Collective Effects)

- Decay Ring HW for RF System Studied

- Costing (big issue and we need also HW people to work on it)

- Beta beam potential => The need for duty factors:

- SF = Separation Factor = Duty Factor => To suppress the atmospheric background (we want to have in a short time the maximum of the intensity, not to confuse with the atmospheric background).

- With a SF as small as 0.01% sensitivity is almost as good as if there were no atmospheric background.

- If we could have a SF between 1% and 0.1% we could be competitive.

- We 1st need to know the θ₁₃ and then we could go to the CP violation.

- We don't know yet if beta-beams will be good or not. If θ₁₃ is very small then we can forget about it! Some hints could be given by T2K (Reminder on the T2K = Tokai-to-Kamioka long baseline neutrino oscillation experiment (295 km) => The goal is the discovery of the ν_e appearance (θ₁₃). Physics data taking started on January 17, 2010). The 2012 date was chosen to have the answer on the θ₁₃ range from T2K.

- Reminder: For long baselines, we need more intensity in the rings as there is less intensity in the experiment.

- Michel Martini is joining the team => Greenfield and general questions, RFQ and Linac if we cannot get other help.

5) Beta-Beams production ring (EB): ppt

- Reminders:

- In the EURISOL scheme, we use a proton machine and send protons on a target.

- In the EUROnu scheme, we study 8Li and 8B, and use a multi-turn interaction with a target. Idea from C. Rubbia et al., but the same year Y. Mori had also the same idea using a FFAG (scaling FFAG, where the chromaticity is 0 for all the orbits), and he built it (BNCT = Boron Neutron Capture Therapy), with similar parameters as ours.

- Production ring:

- Compact ring & thin internal target

- Enhance production 8Li/8B (~10¹⁴/s) by multi passages trough the target

- Inverse kinematics: Li beam @ ~25MeV and D or 3He supersonic gas-jet target

- Multi Coulomb Scattering + energy straggling @ target

- Ionization cooling

- The cooling will be done by ionization cooling => Using the target we produce the ions AND we cool them.

- Only the longitudinal component recovered by RF cavities => Transverse emittances shrink.

- Need coupling between longitudinal and transverse (as the cooling is not so efficient in longitudinal) => Dispersion and wedge-shaped target.

- It fact this cooling is not so efficient: not real cool the beam but slows down the emittance growth.

-  A lattice is proposed.

- Tracking simulations performed with SixTrack, adapted to the production ring needs (target implemented as a special collimator element, ions instead of protons => Proton equivalent ring, etc.):

- The transverse emittance increase is linked to multiple scattering => We should decrease the betatron function.

- ~ 10000 turns are needed for the particle production but it is limited to ~ 1000 turns.

- Technical challenges:

1) Production of stable Li in ECR-source => Factor > 10 missing compared to what is done today (but we can imagine to have many sources in //, it is therefore not a complete showstopper).

2) Collection device: 2 microm Tantalum foils + Extraction by heating-up => Issues:

- Diffusion/effusion efficiency

- Small angle (θ ~ 10 deg) of products => Needs collection device close to the beam, but it can intercept it!

3) Supersonic gas jet target => 4 orders of magnitude missing compared to what can be done now.

- Some possible solutions were proposed and another possibility is to use D or 3He beam & Lithium target (solid, waterfall, droplets,?).

- Conclusions:

- Tracking tools for i-cooling studies fully in place and agree with analytical considerations.

- BUT still a lot of work have a feasible solution to produce enough flux of isotopes for Beta-Beams Neutrino physics!

- Reminder from Fritz Caspers: 1 Torr gives wonderful blow discharge when there fields around (typical problem in space?...)

6) Collective effects studies for beta-beams in the decay ring (CH): key or pdf

- Injection scheme in the Damping Ring (DR): The new bunch is injected off-momentum, after a 1/4 of synchrotron turn it is captured by one RF system, and then it is merged into the old bunch with the use of a 2nd RF system. After merging the bunches are ~ 2m long. A collimation system removes the particles with a dp/p above 0.25%.

- Acceleration in the Damping Ring: Due to the collimation and radioactive decay the number of ions per bunch saturates in the DR (20 of these bunches gives Ntot).

- With 20 bunches from SPS to DR, we get SF = 0.58%, i.e. between 0.1% and 1% as required. However, what about collective effects?:

- Laslett tune shifts => Always below -0.1, which is considered to be fine in a pulsed synchrotron like the PS or SPS (a usual limit in a synchrotron is said to be ~ -0.2), but if the particles stay during a long time it can already be an issue. See some space charge observations at PS and SPS: http://accelconf.web.cern.ch/accelconf/HB2008/papers/wga29.pdf and talk.

- Wake-fields in the transverse plane => 3 approaches were compared for 0 chromaticity, i.e. for the TMCI regime:

- Coasting-beam (analytical) formula with peak values

- MOSES (solving an eigenvalue system).

- HEADTAIL (tracking code).

=> Several issues revealed and after the meeting EM and CH discussed the bad agreement between the simple analytical formula, MOSES computations and HEADTAIL simulations. It was found that the 3 approaches should be performed with care:

1) Analytical formula (essentially the coasting-beam formula with peak values) => It is usually given for the average betatron function betaAverage = machine radius / transverse tune. In the present case, the real betaAverage is larger (by a factor 1.6) than that and the formula needs to be adapted. EM checked that for the case of a resonance frequency of 0.5 GHz the agreement with MOSES is within a factor of 2 as usual. The higher resonance frequencies remain to be checked (Action 2: CH).

2) MOSES computations => One has to check that the result is stable, i.e. does not vary with the number of azimuthal modes and in particular radial modes (particularly important in the "long-bunch regime").

3) HEADTAIL simulations => Check each time that enough slices are used (see for instance the ICE talk from KL: https://emetral.web.cern.ch/emetral/ICEsection/Meeting_01-09-10/100805-ICE.pdf).

- Z correction introduced to run MOSES with ions:

- In the MOSES input file, we enter the total energy (which includes the mass number A).

- One then just has to multiply the x-axis (intensity) by Z.

- This was benchmarked against HEADTAIL and it seems to work well.

- Conclusions:

- We have a very challenging upper limit of the DRs transversal shunt impedance => 10 (100) times smaller than SPS for 6He (18Ne) based on HEADTAIL and MOSES studies!

7) Actions to be taken for the next meeting

- Old actions.

- New actions:

- Action 1: BS and NM will perform HEADTAIL simulations to see if the single-bunch instability threshold,  with the IR3MBC collimators, can be increased sufficiently above the ultimate intensity with Landau octupoles.

- Action 2: CH will redo his comparison between the analytical formula (essentially the coasting-beam formula with peak values), MOSES and HEADTAIL.

8)  Miscellaneous

- The next (10th) meeting will take place on 06/10/2010 => Agenda:

1) Space charge studies for PS2 (Ji Qiang, LBNL => Note that he also gave an APF talk "A parallel strong-strong beam-beam simulation code and applications to LHC studies" on TU 05/10/10 at 11:00 in the BE Auditorium => http://lhc-beam-beam.web.cern.ch/lhc-beam-beam/forum/cernbbtalkvnew.pdf)

2) Study of J-PARC Main Ring with the PTC-ORBIT code (Alexander Molodozhentsev, KEK)

- See preliminary agendas for the next meetings.

Minutes by E. Metral, 06/10/2010.