2. Tracking simulations of protons quench test
A. Mereghetti, A. Valloni, R. Bruce, S. Redaelli
on behalf of the LHC Collimation Team
Tracking simulations of protons
quench test
LHC Collimation Working Group
Special thanks to H. Rafique for essential tips & tricks about Merlin
Monday, 7 March 2016

3. Outline The proton collimation quench test:
Introduction;
First comparison between cleaning studies (Fluka-SixTrack coupling) and measurements (BLM data);
Comparison between codes: SixTrack, Merlin and Fluka-SixTrack coupling;

4. The Proton Collimation Quench Test
Aim: to reach HL-LHC type of losses at 6.5 TeV and improve the knowledge of the quench margin of DS magnets due to collimation cleaning leakage;
Two IR7 collimator settings:
2015 operation  h=~4 10-4;
2013 very relaxed settings (mm-kept)  to worsen cleaning inefficiency in case no quench was found with operational settings;
Due to a problem in LSA DB (found only while updating BLM thresholds) the time dedicated to the MD was severely reduced (~3h instead of 10h);
 Time for one ramp only to 6.5 TeV;
Outcome of test: premature dump at ~600 kW beam losses, with no quench induced;
Further infos: B. Salvachua Ferrando et CWG 199th (22nd Jan slides) and documents therein;
B. Salvachua Ferrando et al.199th CWG

5. The Benchmark with Simulations
Numerical simulations:
Energy deposition in superconducting coils: to shed some light on the quench margin;
BLM signals: benchmark the simulation;
Simulation settings:
Optics: B2 injection optics at 6.5 TeV (before Q-change):
no squeeze;
bumps for parallel separation on;
Collimator settings: as in test (i.e. as for 2015 operation);
Beam sampling:
Horizontal plane: constant over s;
Vertical plane: regular Gaussian distribution (no cuts);
Longitudinal plane: Gaussian distribution with 2s cut (sl=75.5 mm, sd= );
Simulations: Fluka-SixTrack coupling, ~64Mp, online aperture check, ‘touches’;

6. Loss Map – Entire LHC Measurements (BLMs, RS09) (Fluka-SixTrack)
Simulations

7. Loss Map – IR7
Measurements
(BLMs, RS09)
(Fluka-SixTrack)
Simulations

8. Loss Map – IR7 DS Measurements (BLMs, RS09) (Fluka-SixTrack)
Simulations

9. Single turn dispersion
Loss Map – IR3
Single turn dispersion
Measurements
(BLMs, RS09)
(Fluka-SixTrack)
Simulations

10. Loss Map – IR3 zoom 80% above noise Measurements (BLMs, RS09)
(Fluka-SixTrack)
Simulations

11. Losses in IR3 – Zoom
40mm
Losses mostly (~70-80%) due to SD scattering on TCP.C6R7;
 Visible also for B2V,B1H,B1V;
BS (22.55mm, 17.65mm)
In agreement with D=~2.8m

12. Loss Map – Touches (2D PDFs)
Negative Jaw
Positive Jaw

13. Code Comparison
Collimation proton quench test gives good opportunity for comparing codes available for cleaning studies:
SixTrack: 6D tracking in thin lens + beam particle scattering;
Fluka-SixTrack: tracking engine of SixTrack + full MC functionalities of Fluka;
Merlin: 6D tracking in thick lens + beam particle scattering;

14. Sampled input distribution
X –X’
Y –Y’
σ- δ
5.5 σ σ
Transverse distribution
Horizontal beam halo characterised by a ring
shape in the normalised horizontal phase space
Gaussian distribution in the vertical plane
Gaussian distribution in the longitudinal plane
cut at 2σ
Same beam parameters of the previous case

15. Radial distributions Horizontal Vertical Longitudinal
Module of the x-x’, y-y’, σ- δ distributions projected on the radial coordinate
Sixtrack and Coupling  6-D simulations
Merlin  4-D simulations (no RF accelerating cavities)

16. Optics functions
Add Alice in the list of erl based accelerators
Horizontal beta function calculated by SixTrack, Coupling and
MERLIN, as an example of optical functions calculation
Very good agreement for the optics parameters calculated with the three codes

17. Apertures Some differences in apertures observed in Merlin (Markers?)
 makes no substantial differences to the loss maps

18. Loss Maps
SixTrack
Coupling
Merlin

19. Loss Maps IR7
SixTrack
Coupling
Merlin

20. Loss Maps DS region SixTrack 10-4 10-5 Coupling 10-4 10-5 Merlin 10-4

21. Loss Maps IR3
SixTrack
Coupling
Merlin
1.7*10-4
10-4

22. Inelastic losses Inelastic events on TCP.C6R7 max (min) in Merlin (6T)
On the other collimators more inelastic interactions
observable with Coupling
Add Alice in the list of erl based accelerators

23. Sharing of losses Simulated particles Collimator Losses [%] Cold
Warm
Survivors
[%]
SixTrack
6.4*106
0.0925
0.0055
0.2959
Coupling
6.5*106
0.0606
0.0107
0.2742
Merlin
6.6*106
0.0361
0.0015
0.1763

24. Single Diffractive Interactions
Overall more SD interactions observable
with SixTrack
In Merlin much less SD interactions
with respect to SixTrack
Add Alice in the list of erl based accelerators

25. Inelastic interactions on TCP.C6R7
Negative jaw
Positive jaw X’ Y Y’ Z
Sixtrack and Coupling show a very good agreement
Merlin presents particular differences in the X plane

26. Coupling and Merlin show better performances in terms of hs06 seconds
Performances of the codes in HS06 seconds
Coupling and Merlin show better performances in terms of hs06 seconds
Sixtrack requires at least ~ 4* more CPU time  main bottleneck: aperture check is performed as post-processing through large text files (I/O overhead)

27. Thank you for your attention
Conclusions
Proton quench test simulations help to better address the quench margin in SC magnets downstream of IR7;
First comparison between BLM measurements and high statistics cleaning simulations (Fluka-Sixtrack Coupling) shows a good qualitative agreement;
Proton quench MD good test bench for code comparison:
Overall agreement among the three codes  comparable global loss patterns;
Still some differences exist: losses in machine aperture are the highest in 6T and the lowest in Merlin;
Fluka simulations missing step in order to:
Evaluate the actual en. dep. in the IR7 DS during the test and assess the quench margin;
Quantitatively compare predicted loss patterns with measured BLM patterns:
Fluka-Sixtrack Coupling: input for en. dep. studies available;
Merlin: input not yet available as we need to have full control of the 6D tracking;
Thank you for your attention

29. Backup slides

30. The Proton Collimation Quench Test (II)
B. Salvachua Ferrando et al.199th CWG

31. Loss Map – Touches (1D PDFs)

32. Loss Map – Touches (1D PDFs)

33. Inelastic interactions on TCP.C6R7

34. Normalised Losses
Normalised respect to the total number of losses

35. Ratio SD/Inelastic interactions

36. Ratio Inelastic – SD interactions

37. Inelastic interactions - ratio

38. Inelastic interactions - difference

39. SD interactions - ratio

40. SD interactions - difference

41. Optics functions: Dispersion

42. Optics functions: Dispersion

43. Optics functions: alphas

44. Optics functions: closed orbit