CERN Space Charge Studies 2012/2013 The CERN Space Charge Study Group Information, Learning, Database My professional plans General Program 2012/2013 Computing Resources Studies of PSB, PS, SPS Intro to DT Measurement 1

Material from the Participants General PTC-ORBIT strategy: Alexander Molodozhentsev PSB: Christian Carli, Elena Benedetto,Vincenzo Forte, Miriam Fitterer PS: Simone Gilardoni, Raymond Wasef; Massimo Giovannozzi, Cedric Hernalsteens (MTE) SPS: Yannis Papaphilippou, Hannes Bartosik 2

The CERN Space Charge Study Group The main idea of this study group is to create a Forum to discuss space charge issues for the LIU upgrade. The idea is to see once or twice per month and discuss in full depth technical issues. The style should be informal and we should concentrate on problems, i.e. polished presentations are not desired. In particular, younger colleagues should have a place to ask question and get answers. SERVICE: – web page with lots of useful features! 3

Web Page Mandate Core Team and collaborators Meetings Literature Web address: cern.ch/frs/Source/space_charge Mandate Core Team and collaborators Meetings Literature Parameter_List PTC-ORBIT Codes 4

My plans Space charge activity at CERN Forum for in-dept discussions Documentation of the effort Database for information and help Support of students if required Participation at experiments at all 3 machines Constructing effective nonlinear models Collaboration with GSI and Fermilab Travel to Fermilab (August – December) The long exit from LHC work: I stepped down from MAD-X and SixTrack Was asked to resign from PTC Non-linear studies finished this year Still some knowledge transfer Various reports to be written 5

General Program 2012/2013 - 1/2 Gradual upgrade of computing resources Effective model of the machines: MAD-X lattice with all known imperfections and possible locations with unknown imperfections. Push measurement effort (actively pursued for PS) Get expertise from magnet experts  Fidel Measure localized nonlinearities with DT technique Intense Measurement program in 2012 NO measurements possible in 2013 Tune scans with SC DT measurements Intense Optimization effort for PTC-ORBIT (Harry Renshall) 6

General Program 2012/2013 - 2/2 PTC-ORBIT preparation in 2012 Ideal PTC lattice with imperfections PTC-ORBIT space charge convergence Timing First tests PTC-ORBIT systematic simulation in 2013 Comparison 2.5D and 3D SC model Tune scan GSI collaboration Experiments in 2012 Comparison with 'frozen space charge‘ model MICROMAP GSI proposes "noise filtering" of PIC codes 7

Computing Resources Alexander et al. have performed the benchmarking run on various parallel platforms: Result-0404-2012.pdf I have asked all 3 teams to provide me with a “dream” study program to evaluate how much resources we could possibly manage to use. I am guessing that, we at the pre-accelerators, are not used to demand a lot! I got very timid proposals. My experience from the LHC is that the appetite comes with food (German proverb) and that resources will be used if they are available. Therefore, I concocted a rough estimate that 10 such 48 core machines per team, i.e. a six-fold increase of throughput, would be a reasonable request. IT made that possible and apparently out of their budget! This may be an indication that we didn’t demand aggressively enough… 8

CERN PS Booster study Alexander Molodozhentsev ‘SHORT-dipole’ (Elena Benedetto) vz ‘NORMAL’ PSB lattice  emittance growth analysis … Halo formation at the injection energy … losses in realistic Aperture Effect of the double-harmonic RF system LIU: Machine imperfection and Space charge effects Effects of Basic machine imperfections & resonance correction scheme (DT measurements) Benchmarking with existing results of the emittance measurements at the injection energy (160MeV) Acceleration process  ‘time’ scale of the emittance growth … ‘Bare’ working point optimization during injection and acceleration Multi-turn injection scheme (with FOIL and ‘painting’ process)  dynamic variation of the machine properties during the injection process

CERN PS/SPS study Alexander Molodozhentsev (DT measurements) Emittance growth and Losses  Injection process (with the ‘dynamic’ chicane variation) (not SPS)  Optimization of the ‘bare’ working point during the injection and acceleration Emittance growth and Losses  Injection process (with the ‘dynamic’ chicane variation)  Optimization of the ‘bare’ working point during the injection and acceleration LIU: Machine imperfection and Space charge effects Effects of machine imperfections and resonance correction (DT measurements) Effects of machine imperfections and resonance correction Benchmarking with the emittance growth measurements Time scale of the emittance growth due to the combined effects of the machine resonances and the space charge during the injection / acceleration Effects of the longitudinal splitting at the injection energy (not SPS)

CERN PS Booster in practice Vincenzo Convergence Study is under way and basically done Including the vacuum chamber one may create unphysical tune footprints. This is a sampling issue of the beam due to a too coarse mesh. For direct space charge mesh size and number of macro particles can be relaxed. Miriam Impact of Lattice Properties on Space Charge Limit variation of beam size and ration between horizontal and vertical beam size dependence on periodicity and symmetry dependence on the phase advance per cell

CURRENT STATUS Raymond PS PTC-ORBIT ; For PTC-ORBIT Space-Charge model, a 2.5D model with boundary conditions has been chosen and its transverse mesh parameters and number of particle have been optimized for beams close to LHC_50ns transverse parameters. Few footprints have been made for these beams. A good agreement between the tune-spread predicted by theory and simulation. Resonance Measurement : Driving terms measurement started. Measurements have began but they have been interrupted because the Skew-Quad. are not working properly. 5/28/2018 PS Space Charge Studies 12

Plan for future work Raymond PS PTC-ORBIT ; Start simulating LHC-25ns and check the effect of the integer resonance. Introduce the injection bump and see its effect. Introduce machine imperfections to benchmark the code with tune-scan measurements. Simulate the HL-LHC beams and try to find the “Space-Charge limit” Resonance Compensation: Restarting the measurements for different working points (a scan between 6.1 and 6.4 in horizontal and in vertical). Preparing an effective model to have a better understanding of the driving terms and make the compensation study. Try the suggested solution and verify it by re-measuring the driving terms 5/28/2018 PS Space Charge Studies 13

MTE PS Cedric Re-study mesh study of Andrea Franchi in the MTE splitting case. Mesh might have to adapted continuously. Requiring frequent restarting and re-adapting. Try to simulate the linear dependence of the beamlets position vs. total beam intensity (see next graph). Disentangle direct space charge of the beamlets and core from the image charges. New theoretical approach likely to be required!

Reserve TMCI threshold can be increased by increasing chromaticity or longitudinal emittance 15 15

SPS and DT Measurement SPS 2012.05.06_SpaceChargeStudies_SPS_hannes.pptx DT Measurements OMCM_GSI_11.05.2012.ppt

Reserve

PTC-ORBIT @ PS (Simone) Needs: Simulate eventual emittance blow-up of high-intensity LHC beams (for PS upgrade or not…) Help in determining the maximum acceptable Laslett tune spread, i.e., maximum intensity per bunch and/or minimum emittance Identify, if possible, an eventual cure (resonance compensation, change of working point?) Understand continuous losses observed during the injection process of the high intensity non-LHC beams 18

Space charge simulations for SPS (Hannes) Motivation High intensity single bunches are produced since 2010 and injected into SPS A series of parallel MD sessions were dedicated to finding intensity limitations first with the nominal LHC optics and later with the new low γt optics (which should provide higher beam stability) Space charge tune spread of ΔQ~0.05 for nominal LHC beams (1.3e11 p/b, εn,xy=2.5 μm) Recent studies with up to 3.3e11 p/b and injected emittances of εn,xy~1.2-1.5 μm ==> significantly increased space charge tune spread (ΔQ~0.15 and higher) MD sessions are currently devoted to studies of emittance preservation for high intensity and working point optimization Working point optimization should/could be accompanied by space charge simulations with PTC-ORBIT Benefit/relevance of PTC-ORBIT for SPS space charge simulations Ultimate goal is to develop an “effective” machine model including the nonlinear (multipole) components of the machine (presently ongoing) and use this model for optimizing the working point in the presence of space charge tune shift For this purpose, PTC-ORBIT seems to be a suitable tool … TMCI threshold can be increased by increasing chromaticity or longitudinal emittance 19

Do we need PTCORBIT for our space charge Studies? My personal View… I have asked the following questions to the PSB, PS & SPS collaborators: A) Do you consider PTCORBIT relevant for the analysis of your machine? B) I know that for the PSB the demands on the features of PTCORBIT are most relevant and it seems that there is still a need for more development that we should ask Etienne for, if we decide to go for PTCORBIT. Personally, I think we should continue this development even if it is not easy to communicate with Etienne nor with Sasha. Etienne is properly the one to fix the remaining problems with PTCORBIT. C) My general feeling has been that one might need a closer look at the optics models of all 3 machines. Please excuse me, since I am coming from the LHC and we had the luxury to measure everything and have very sophisticated models. This will be difficult to do for these reliable but old machines nevertheless we should make our best effort to come up with the best we can know about those machines. Of course, we need sufficient manpower to do so! Do you agree with this analysis? D) Most exciting is the fact that apparently Hannes has found issues with the results of his space charge calculations in ORBIT itself. It would be great if Hannes could elaborate on this a little bit. After all, the PTC part is only single particle part to serve ORBIT. 20

Present status of PTC-ORBIT simulations for SPS Ideal lattice used for beginning Nominal and low γt optics – ideal lattice without field errors or misalignment Static magnetic fields and RF-voltage ==> very simple case, no acceleration Actual configuration of travelling wave RF-cavities is modeled (thanks to a modification in PTC) “2.5D” space charge model is used Around 2500 transverse space charge nodes around the lattice 1 longitudinal space charge kick 2.5D simulation is good approximation for “long bunches”: longitudinal size much bigger than transverse size (should be satisfied in SPS for LHC beams, full bunch length around 1.1m and transverse beam sizes on the order of a few cm) For now, beam pipe is not included in simulations Beam size much smaller than vacuum chamber ==> only small contribution to tune spread expected from wall effects Taking wall effects into account requires huge grid size compared to beam size and therefore long computation time Full 3D simulation would require vacuum chamber definition Again the problem of the small beam size compared to chamber size Unpractical due to the different kind of vacuum chambers in the SPS TMCI threshold can be increased by increasing chromaticity or longitudinal emittance 21

First simulations - Observations Simulated one set of parameters for both optics cases to gain confidence in code Intensity 2e11 p/b, emittances εn,xy~2.5 μm Phase space distributions matched to the corresponding optics functions and bucket sizes of the respective optics: Transverse: Gaussian cut at 3σ Longitudinal: parabolic with a cut around 2.2σ Nominal working points for the 2 optics (ξx,y=0.1) Low γt: (Qx, Qy)=(20.13, 20.18) Nominal optics: (Qx, Qy)=(26.13, 26.18) Simulation of 3000 turns (~60ms) Low γt opics: Emittance blow-up <1% in both planes Nominal optics: Significant emittance growth in horizontal plane: initially exponential growth by a factor of 1.5 and beam halo formation!?? Minimal emittance blow-up (<1%) in vertical plane!! Not physical, still under investigation … 22