Injection protection with TDI-TCLI

1. Injection protection with TDI-TCLI • Introduction and scope • Parameters and Assumptions • Simulation methodology • Simulation results • Implications for TCLI design • Future work • Summary

2. Introduction and scope • Failures of LHC injection kickers are protected against with TDI and TCLI collimators (with TCDD mask). • TDI and TCLI are 2-sided moveable objects. • TCLI locations already defined by phase advance • TCLI spec. required (robustness, tolerances, settings) • Simulated protection level as a function of system (TDI + TCLI) aperture. • Checked utility of TCLIs (simulated with, without) • Treated IR8 only (but should hold for IR2)

3. Overview of injection region (IR8) TCDD MKI MSI TDI TCLI2 TCLI1

4. Which failures…? • Most dangerous case is where whole beam grazes TDI face…. • This can happen in several ways: • Wrong settings (kicker, TDI, correctors, …): • can in principle be ‘prevented’ by interlocks and/or adequate procedures. • MKI flashover • no defence – rely on passive protection AND rareness of the event. Taken as worst case for simulation

5. Simulation methodology • Derive particles outside aperture for quoted errors and failure case, as a function of system (TDI plus TCLI) aperture • Beam2 particles are tracked with MADX through TI 8 and injection region of LHC • TDI (4 slices), TCLI1 and TCLI2 included. • Generate typical random TL error pattern with ‘max’ y offset at MKI • Introduce phase errors in Q4 • Scan aperture over range of interest (define TDI, TCLI settings) • Scan MKI kick over range of interest (for scan: MKI as single kicker) • Track particles through, counting losses at TDI and TCLIs • Calculate number of particles in LHC above aperture limit • Calculate max. p+ into LHC vs. aperture • Calculate risk of damaging flashover vs. aperture • Calculate load on TLCI vs. aperture • Simulated with 1000 p+ (interested in 5% statistics) • Gaussian beam in y, y’

6. +0.13 mrad MKI kick 241 steps -0.13 mrad 6s Aperture setting 41 steps 10s Simulation ranges *the quoted (OB) tolerance on k Q4 is 20 units = 2 x 10-3, which translates to a phase error of about 3 x 10-3 rad, or an offset of about 3 x10-2sy – hence this was neglected in the analysis (given the ~0.1 s step sizes)

7. What was included…. • Assumed normal distribution of various errors, derived 95% confidence limit (2srms) as representing max. level for the combination of these errors at the moment of the rare kicker failure • Injection error (y) ±0.45 mm at injection point • SPS orbit errors (0.1 mm / 1 mrad rms in SPS) • Transfer line magnet ripples (used quoted PC tolerances in MAD) • Transfer line drifts (assumed 0.2 mm rms at injection point) • TDI mechanical ±0.2 mm • TCLI mechanical ±0.075 mm • Orbit precision ±0.05 mm (setup with intermediate beam) • Coldbore aperture 8.2 s(for n1 = 6.8) • Damage limit 2.4 x 1012 p+ (5% of full batch) • MKI-TDI phase error 20˚ (made by change of ~20% in Q4 kick!) • 288 x 1.7 x 1011 p+ injected • Gaussian beam in y, y’ Values from J.Wenninger, M.Lamont, L.Bruno, V.Maire, O.R.Jones and O.Brüning

8. What was neglected… • Sweep effect of MKI kicker • Will slightly (few %) improve situation as regards beam into LHC above aperture limit, and load on TCLI. • Will be much more important when looking at losses in LHC at aperture limits at injection. • Apertures (but checked > ~9s in IR 8) • Transfer line failures (magnet trips – MSI, MCIAV, …). • More complete analysis to be made with same tool • Will also include TCDI (performance quantification)

9. Results Load on TDI slices 1 and 4 for +20 deg phase error

10. Results Load on TCLI1 and TCLI2 for +20 deg MKI-TDI phase error

11. Results Load on TCLI1 and TCLI2 for -20 deg MKI-TDI phase error

12. Results Beam above 8.2 sy in LHC for +20 deg MKI-TDI phase error, with and without TCLIs Without TCLIs With TCLIs

13. Results Maximum beam above 8.2 sy in LHC, for cases considered Vertical aperture in s for 5% protection limit

14. Results • Attempt at risk ‘quantification’ • Consider only MKI flashover case (probability of settings error??) • Assume same results apply for IR 2 • Assume 1 MKI flashover per 8 magnets per year  ±0.2 mrad kick per MKI

15. Results Max. load on TCLIs TCLI1 TCLI2 • Even for zero phase error, TCLIs help (better tolerances…) • - intercept 10-18% for TCLI1 • - intercept 2-6% for TCLI2 (location not v. good ~15m by) • For 20 deg phase error, can intercept ~40% of beam

16. Proposed TCLI specification • 1.2 m long jaw of C (hBN, …?) • Surface flatness 0.1 mm • Positioning accuracy ±0.025 mm • Cooling? Depends on beam heating… • Bakeable • TCLI2 at Q6 – looks identical to TCS… check integration • TCLI1 at D1 - common beampipe (maybe looks like proposed D1 TCT, but with low-Z jaw on other beam?)

17. Errors giving min. H separation between beams IP2 (V6.4) Looks close (TCLI collimates but beam 2 close to jaw) - can reduce jaw width by 5mm in direction of beam 1… - make more detailed study to check aperture (mech. tolerance etc.)

18. Errors giving min. H separation between beams IP8 (V6.4) Looks OK (TCLI collimates and beam 2 does not interfere)

19. Summary • With TDI and TCLIs, 0.05 dangerous events per y, for aperture of ~7.75 sy • TCLIs improve the protection even without MKI-TDI phase errors  gain ~0.25 sy in aperture for same protection level • For large (20˚) MKI-TDI phase errors, with TCLIs gain ~1.0 sy in aperture for same protection • TCLIs may allow some tuning of the injection optics, e.g. if need MKI-TDI phase advance ≠ 90˚…. • TCLIs desirable, to cover specified errors and to allow flexibility in operational protection strategies • Recommend robust (C, hBN, …) 1.2m long TCLIs • Maximum beam loads on TCLIs can be 10-40% of a full batch. • Protection with 1.2m C adequate (TCDI analysis: attenuation + emittance dilution) • No worries about beam loads if protection strategy changes – e.g. if TDI has to be retracted more due to unacceptable load from secondary halo… • Vacuum - feasibility seems OK (TCLI1 better than TDI, retracted after injection) • Settings strategy and operational procedures also start to be considered

20. Future work • Completing the MKI flashover analysis • IR 2 • Expected level of load on TCLIs and risk for flashover with ‘real’ pattern of random effects • Secondary halo load on TDI and possible implications… • Evaluation of possible optimised positions (higher by for TCLI2, separate beampipes for TCLI1, …) • Extension to other ‘injection’ error scenarios • Single failures in SPS / transfer lines / injections (septa, dipole families) (especially horizontal plane…) • Check worst-case combination of random effects without any failure • Losses at other apertures (line + LHC aperture models) • Evaluation of mismatch into LHC from tilted line, plus expected mismatch (with errors) after correction • Losses at LHC aperture limits during first turns at injection • Include kicker waveforms