1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. Computing Resources
Alexander et al. have performed the benchmarking run on various parallel platforms: Result 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

9. 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

10. 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)

11. 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

12. 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

13. 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

14. 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!

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

16. SPS and DT Measurement
SPS _SpaceChargeStudies_SPS_hannes.pptx
DT Measurements OMCM_GSI_ ppt

17. Reserve

18. 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

19. 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~ 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

20. 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

21. 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

22. 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