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

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;

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 al., @ CWG 199th (22nd Jan 2016 - slides) and documents therein; B. Salvachua Ferrando et al.199th CWG

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 5.5-5.54s; Vertical plane: regular Gaussian distribution (no cuts); Longitudinal plane: Gaussian distribution with 2s cut (sl=75.5 mm, sd=1.129 10-4); Simulations: Fluka-SixTrack coupling, ~64Mp, online aperture check, ‘touches’;

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

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

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

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

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

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

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

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;

Sampled input distribution X –X’ Y –Y’ σ- δ 5.5 σ - 5.54 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

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)

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

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

Loss Maps SixTrack Coupling Merlin

Loss Maps IR7 SixTrack Coupling Merlin

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

Loss Maps IR3 SixTrack Coupling Merlin 1.7*10-4 10-4 1.5 10-5

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

Sharing of losses Simulated particles Collimator Losses [%] Cold Warm Survivors [%] SixTrack 6.4*106 99.6061 0.0925 0.0055 0.2959 Coupling 6.5*106 99.6545 0.0606 0.0107 0.2742 Merlin 6.6*106 99.7861 0.0361 0.0015 0.1763

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

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

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)

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

Backup slides

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

Loss Map – Touches (1D PDFs)

Loss Map – Touches (1D PDFs)

Inelastic interactions on TCP.C6R7

Normalised Losses Normalised respect to the total number of losses

Ratio SD/Inelastic interactions

Ratio Inelastic – SD interactions

Inelastic interactions - ratio

Inelastic interactions - difference

SD interactions - ratio

SD interactions - difference

Optics functions: Dispersion

Optics functions: Dispersion

Optics functions: alphas

Optics functions: closed orbit