Minutes of the ICE section

10th meeting on Wednesday 06/10/2010 (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, Alexander Molodozhentsev (KEK), Eirini Koukovini Platia, Fanouria Antoniou, Hannes Bartosik, Ji Qiang (LBNL), Max Von Melchner (German student for 2 weeks), Michel Martini, Rama Calaga, Theodoros Argyropoulos, Uli Wienands, Yannis Papaphilippou.

1) Newcomers / visitors

- Ji Qiang (LBNL) and Alexander Molodozhentsev (KEK) who would will give the 2 talks of today.

2) Comments on the minutes of the 9th meeting + Actions

- EM made a small summary of the last minutes mentioning that they are not yet finalized and that they should be released by the end this week.

- List of Actions.

3) General infos

- No particular comment from anyone.

- SL meeting last week:

- India collaboration => Impedance computation for injectors and LHC.

- Publication of LD -> IC posts took place as foreseen on October 4th.

- SPSC asked for 60 days of fragmented ions operation in 2011; Ar run in 2012 as a preparation for 2013 run.

- Neutrino beam to Finland was proposed and should start operation in 2013.

- Australia is trying to become an Observatory member (Brazil will be the first one).

- Computing: no additional resources will be made available, but Paul Collier suggested to follow-up the software support with IT.

- MAD-X responsibility: a long-term solution should be found and is currently under discussion.

- LMC actions for ABP:
        - Aperture measurement at top energy to determine minimum beta* (Massimo et al.)
        - Beam-beam studies for 75 ns and 50 ns schemes (Elias)
        - Repeating/understanding the k-modulation results for IR8 (Rogelio et al.)

- LHC 8:30: another attempt to run with 150 bunches was prematurely stopped after four hours (UFO). ATLAS saw large background.

- News on the LHC:

- Few days ago a new record was achieved in the LHC with 200 bunches times 200 bunches:

• New peak luminosity record ~ 0.68E32.
• Integrated lumi after 12 h > 2 pb-1.
• ~ 2E13 p/beam => 11.2 MJ per beam.
• Pending issue: Vacuum pressure increase near the IPs in the presence of both beams. Reminder from Miguel Jimenez: The triplets are polluted i.e. they were not baked-out, meaning that it is normal that some outgassing is observed (water is present there etc.). Are there other effects involved? HOMS, ecloud etc. To be followed up.

- HB2010 workshop last week => Proceedings already online: http://hb2010.web.psi.ch/proceedings/html/sessi0n.htm.

- Beautiful (revolutionary?) talk by Sergei Nagaitsev on Nonlinear optics as a path to high-intensity circular machines.

- In Vladimir Kornilov's talk (on the effect of space charge on head-tail instabilities) it seems from simulations that the head-tail mode can change with intensity.

- Discussions with Oliver Boine-Frankenheim:

- A CERN student could come to GSI to learn how to use their longitudinal code LOBO and in particular to try and implement one of its module (nonlinear longitudinal matching) in HEADTAIL to improve our longitudinal matching => A possible candidate could be Christian Hansen.

- Vladimir Kornilov could come to CERN for some time to work on Head-tail and/or TMCI measurements with space charge or other collectives effects. Still under discussion to arrange a possible visit: may be we could have Vladimir here while Christian is at GSI (i.e. for ~ 2 weeks).

-  Sheng Wang (from China) gave 2 talks on Tuesday 05-10-10: (1) The Introduction to CSNS Accelerators and (2) Commisioning issues of BEPCII. Na Wang was also with him and we had several discussions with her on some of her work on impedances => See links on the impedance web page: "Coupling impedance and collective effects in the RCS ring of the China spallation neutron source" N. Wang, PhD thesis in Chinese (pdf) and "Longitudinal wakefields and impedance in the CSNS/RCS" N. Wang, Q. Qin, EPAC 2008 (pdf). In particular she extended Tsutsui's results for kickers in the case of a non-ultrarelativistic beam, which is of great interest for us.

- EM had some discussions with Marc Timmins on the DS collimators and Francesco Bertinelli on the LHC PIMs => No time to discuss them in detail during the meeting but the slides are available: LHC DS collimators (EM) and LHC PIMs (EM).

- Decision on the position of the SLAC collimator => To be finalized by OB and EM by the end of this week.

- Last SPSU meeting => 2 questions for our section:

1) Mauro asks for a plot from GR to see the effect on ecloud vs. SEYin particular below the threshold.

2) Question from Elena Shaposhnikova => If we have optics questions (in particular Aperture), who should we contact => I said OB.

- EM + Rama + FrankZ made an MD in the SPS on 23/09/10 in preparation of a possible installation of a KEKB crab cavity to look at the beam lifetime and transverse emittances evolution with a single bunch in coast at 55 GeV/c and the results were not so good => Over ~ 1.5 h of coast more than 10% decrease in intensity was observed and more than a factor 2 of transverse emittance blow-up.

- BS&co continued measurements of TMCI in SPS injection with a nominal LHC bunch (except the intensity) => It seems that the intensity threshold is ~ 1.7E11 p/b for the lowest chromaticity, i.e. ~ 0 but still positive, (our theoretical estimate is ~ 1.4-1.5E11 p/b) and then the threshold increases rapidly with chromaticity.

4) Space charge studies for PS2 (Ji Qiang, LBNL): pdf

- Reminder on the PS2 with a proposed intensity of 4E11 p/b and an injection energy of 4 GeV.

- Ji Qiang explained the computational models before showing first the usual initial benchmark with 0 current and then space-charge simulations of PS2 where the following effects were discussed: Synchro-betatron coupling, initial painting schemes, RF ramping schemes, initial beam emittances and bunch intensities.

- IMPACT-Z: parallel PIC code (z-code) and IMPACT-T: parallel PIC code (t-code). Already applied to many projects.

- Split-operator method: H = Hexternal + Hspacecharge.

- // implementation: domain decomposition vs. particle field decomposition.

- 1 billion macroparticles could be simulated in some cases (FEL linac).

- Caution: For the RF voltage, what is called New RF voltage is in fact the programme from Steve Hancock and the Nominal one was in fact a first approximation.

- GR asked why the chromaticities were corrected (using therefore sectupoles) in this machine as it should operate always below transition.

- It seems that the longitudinal painting was studied in some detail but not the transverse one (correlated vs. anti-correlated etc.).

- Alexander Molodozhentsev mentioned that the injection bump should also be considered in the studies.

- Yannis asked about the possibility to add or not the fringe fields in the code, which is indeed possible.

- In summary, it seems that space-charge effects can cause significant beam emittance growths and particle losses at PS2.

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

- AM started by an overview of J-PARC:

- Linac + RCS + Main Ring (MR).

- RCS has in fact 2 users: MR (5 %? of the time) and "MLF (Material...) facility" the major part of the time.

- MR has 2 users also: "Hadron area" (slow extraction) and T2K (fast extraction => Neutrino line).

- MR injects at 3 GeV and extract at 30 GeV instead of the foreseen 50 GeV. This is due to the strong saturation of the main dipoles, in particular close to 50 GeV => There is a very big sextupole component, which perturbs considerably the beam dynamics (but in principle they should be able to go to 50 GeV from the magnet point of view). The nominal tunes were 22.4/22.8 but they were changed after optimization.

- 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. Beam power up to 100 kW is delivered to T2K.

- Linac => H^- injection, 181 MeV at present (400 MeV foreseen in 2012).

- AM continued with reminders about the PTC code and the ORBIT code:

- PTC (Polymorphic Tracking Code) => See publications by Etienne Forest:

- PTC is a library of magnet routines programmed in Fortran90 that makes use of the Full Polymorphic Package (FPP). PTC implements symplectic integration and provides structures for the description of a beamline.

- A particle going through a beamline element sees only the local magnetic field, and PTC uses a local reference frame for describing that magnetic field - the frame most appropriate for the geometry of that type of element. To track through a series of beamline elements, PTC locates the elements with respect to each other using geometric transformations that connect the reference frame of one element to the reference frame of neighboring elements.

- The 2 central features of PTC are:

- Fortran90 types that allow the full three-dimensional placement of beamline elements and the construction of non-standard accelerator topologies: colliders, recirculators, dog-bones, and combinations of these topologies,

- Full usage of Taylor maps derived from the integrator for the computation of lattice functions and other accelerator properties.

- ORBIT (Objective Ring Beam Injection and Transport code):

- Object-oriented, open-source code started at SNS to simulate high-intensity rings.

- Particle tracking code => Macroparticles in 6D, using s (instead of t) as independent variable, using PIC for collective effects simulations, using a set of nodes for the accelerator lattice.

- It incorporates a sizeable collection of physics, engineering and diagnostic models => Many models.

- The basic lattice preparation should be made by MAD8 and alignment errors for different types of magnets should be made inside ORBIT, which does not seem to be the best thing to do.

- 2.5D (the transverse space charge force is weighted by the local longitudinal density) or 3D space charge module algorithms.

- The idea to combine the 2 codes came after discussion at the HB2006 workshop. It was realized in 2007 with a KEK-SNS collaboration.

- Nsc-node is the number of space charge kicks along the machine. For the MR ~ 1500 have to be used otherwise an artificial emittance blow-up is observed. This huge number of nodes is explained by the fact that the betatron functions vary a lot and one has to resolve the oscillations.

- In a plot shown by AM, it is seen that going from 20E4 particles to 40E4 particles, the emittance growth decreases, but are we sure we reached the saturation level?

- PTC-ORBIT is installed on the KEK Super Computer system HITACHI SR11000 (AM told us that Blue Gene was not as good).

- How does PTC-ORBIT(MPI) work? => 3 steps:

1) STEP1 (in combination with MADX):

- Machine description by MADX or by PTC itself

- Machine study: lattice properties (linear / nonlinear), tune variation

- Chromaticity correction

- Full power of MADX and/or PTC can be used at this level

2) STEP2 (PTC or MADX-PTC):

- Single particle dynamics study

- Resonance observation and correction

- Preparation (by PTC) for the multi particle tracking by PTC-ORBIT

3) STEP3 (PTC-ORBIT):

- Multi particle dynamics without/with the space charge

- All possibilities of ORBIT can be used, in principal...

- Studies of resonance-induced beam losses for the Main Ring (maximum power lost 450W)

- Computational model as realistic as possible: all magnet nonlinear components and field leakage from injection septum + 6D beam distribution => 2 studies:

- MR at low power (single particle) => Experimental and numerical tune scans to indentify the main resonances (most critical is sum Qx + Qy = 43)

- Origin: CO distortion on sextupoles

- Exercise: Controlled deformation of CO orbit in sextupoles to create linear coupling + compensation scheme => Works! But they prefer to use skew quads to correct the coupling (to avoid bumps and therefore potential aperture issues), this is why some skew quads will be installed during the next shutdown.

- MR with moderate power => Try and find the best working point and there is a good agreement between simulations and measurements.

- For the moment the beam power is only ~ 0.1 MW. The idea is to go to ~ 0.4 MW in 2 years and then to go to 1 MW and finally even more (~ 1.5 MW)...

6) Actions to be taken for the next meeting

- Old actions.

7)  Miscellaneous

- There will be no meeting next week on 13/10/10 due to the HE-LHC10 workshop.

- The next (11th) meeting will take place on 20/10/2010 => Agenda:

1) News on some kicker impedance studies (CZ)

2) News on some other impedance studies (HD)

- See preliminary agendas for the next meetings.

Minutes by E. Metral, 07/10/2010.