1. TATIONpRÆSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET High Energy Collimator Recommendation H.D. Thomsen, S.P. Møller (ISA, Aarhus University) M. Eshraqi, R. Miyamoto, E. Laface, T. Shea, E. Pitcher, A. Nordt, L. Lari, L. Tchelidze, H. Danared, P. Ladd (ESS) S. Wronka, K. Szymczyk, P. Warzybok (NCBJ, Swierk) 1

2. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET HEBT Layout + Collimator Baseline 2 μ x,y = 60° ≠Neutron Shield Wall! Single-stage

3. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Beam Expander System 3 Focusing = (Lin. – non-lin) PBW Dogleg

4. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Collimator Workshop, 13-14 May, ESS: “Beam Losses and Collimators in Transfer Lines” ›11 external experts at hand: CERN (6), SNS (1), KEK (1), PSI (2), GSI (1) ›Uncontrolled losses? Focus on ~2 GeV ›If possible, beam should be stopped at lower energies. ›Solution & experience sharing! Collimation strategies? ›Visiting labs: collimators are being used to (HDT’s impression): ›Reduce operational beam losses: Prepare the beam for a next-stage accelerator (typically ring-based) ›Protect sensitive accelerator hardware (e.g. SC magnets) ›Clean beam downstream of parasitic secondary beam production targets (PSI) ›Workshop recommendations: ›Experience from similar operating facilities should be studied with the SNS being the lead candidate. ›Beam physics studies should be performed to fully determine the need for collimation. Be very specific in purpose! Every-day operation & infrequent catastrophic events. ›If possible, consider a more global collimation strategy, i.e. MEBT + HEBT collimator performance? 4

5. R. Bruce, 2014.04.15 General design considerations When designing an accelerator facility: Do we need collimators? Where should collimators be installed? – Global/local protection? – Betatron / momentum collimation? Multi-stage system? Movable devices or fixed masks? What material? What simulation tools do we have? Design choices depend on losses we want to protect against

6. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Inter-Diciplinary Ad-Hoc Working Group Kick-off meeting late August. ›ISA, Denmark: H.D. Thomsen, S.P. Møller ›ESS: M. Eshraqi, R. Miyamoto, E. Laface, T. Shea, E. Pitcher, A. Nordt, L. Lari, L. Tchelidze, H. Danared, P. Ladd, S. Molloy ›NCBJ, Poland: S. Wronka, K. Szymczyk, P. Warzybok ›Linac + HEBT beam physics, beam instrumentation, target, machine protection, beam loss simulations & shielding, vacuum, mechanical design, … Conclusive proposal: ›No clear justification for the existing HEBT collimator systems. Remove them from the ESS baseline design. ›Reducing the overall project contingency a tiny degree. ›Continue collimator design, but not construction, to be prepared for surprises? ›(Another discussion: how far?) 6

7. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET A SIMILAR FACILITY The Oak Ridge Spallation Neutron Source 7

8. M. Plum – ESS Beam Losses and Collimation wkshp May 2014 8Managed by UT-Battelle for the U.S. Department of Energy SNS Scrapers and collimator locations RTBT HEBT Injection Extraction RF Collimators In MEBT: Left-right, top-bottom scrapers In HEBT: Two pairs of left-right scrapers Two pairs of top-bottom scrapers Two collimators In HEBT: Left-right (high and low momentum) scrapers Followed by beam dump In Ring: Four scrapers (0, 45, 90, 135 deg.) Three collimators Most effective Occasionally used Scrapers almost never used Rarely used In RTBT: Two collimators Target protection ESS – no ring: Small emittance Strictly single-pass Beam quality?

9. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET ESS (5 MW, p) vs. SNS (1.4 MW, H - )? Shishlo et al., IPAC'12, TUOBA03 (2012), Intra-Beam Stripping (IBST): The reduced beam loss for protons implies that a proton SCL should be able to provide several times higher power with the same low activation and ``hands on'' maintainability as the existing SNS linac. SNS HEBT? Beam debunches -> IBST not a concern. 9 H-H- p H -, I p 2 p, I p

10. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET BEAM STUDIES Operational Beam Losses: activation, material deterioration, etc. 10

11. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Simulating the HEBT Halo? Injection @ HEBT s = 0 ›Two-component beam, (core + halo) ›Typically 2 x Gaussians ›ε h / ε c = 5 ›N h / (N h +N c ) = 1% ›6D: transverse + longitudinal End-to-End, ESS Acc. Phys. ›4D Gaussian is fed into the RFQ ›MEBT->DTL->SCL->HEBT ›Time-consuming but can be rewarding (long. effects) 11 Errors (stat + dyn) can be applied to both approaches

12. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Injection: HEBT Error Studies 12 IPAC’14, WEPRO074: 1000 HEBTs x 10 6 particles: STAT (+ corr) + DYN Errors No losses until target monolith (<100 W)

13. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET End-to-End (ESS Beam Physics Group) HEBT: ›Low-energy protons (300-600 MeV) ›E < 800 MeV are lost inside the first dipole 13 RFQ output R. Miyamoto, HB2014, MOPAB18 +Errors 10 3 x10 5 -Errors 1x10 7

14. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Also seen @ SNS Achromat to Ring? 14 mrem / hr 10 mSv/h

15. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET “Alternative”: Normalized HEBT Aperture 15 SNS HEBT: 15 – 24 @ 1.4 MW APT HEBT: 80 @ 100 MW

16. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET 16

17. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET 17 HEBT Aperture

18. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET BEAM STUDIES Accidental Beam Losses: accelerator component damage 18

19. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Timescales of Component Failure Initiating event: The failure of an accelerator component leads to dramatic beam parameter changes. Result: Beam losses are increased dramatically at downstream (key) locations. Collimators can buy time before beam-induced accelerator component damage. Timescale τ f of the initiating event is important in order to determine response time of mitigating system. ›FAST: τ f < 2.86 ms, beam parameters can change considerable during a pulse ›RF (arcing) ›Low-inductance magnets (raster system?) ›MODERATE: τ f > 2.86 ms, impact can build up over a number of pulses ›High-inductance magnets (conventional magnets) 19

20. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Case 1: RF Failure, ∆E = 0 MeV 20 ∆y < 0.33 mm/MeV

21. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Case 1: RF Failure, ∆E = -100 MeV 21 ∆y < 0.33 mm/MeV

22. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Case 1: ∆E, Impact @ BEW 22

23. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Case 2: Raster System ›8 raster magnets (4H + 4V). ~40 kHz triangle wave, nom. ±2 mT.m (max. ±5 mT.m) ›Failure cases: ›2a: full failure. Beam is left static on target and PBW. ›2b: Excessive amplitude? ›2c: Internal synchronization? ›Only 2b could possibly be mitigated by collimation. Part of Target Monolith? 23

24. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Case 3: Final Doublet, 71 ms failure in QP5 24

25. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET “Alternative”: Machine Protection 25 Beam can be inhibited within ~20 µs (133 µs of beam corresponds to 1 SNS pulse)

26. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET Summary ›No universal collimator design available: focus on actual problem(s) in our unique machine! ›SNS: ›H - problem: irrelevant to collimation questions ›HEBT collimators only applied to make small improvements to the beam losses. ›MEBT scraper system has been upgraded. ESS status & actual problems? ›Transverse halo: does not seem to be a problem. Ample apertures are used. ›BES suppresses beam distribution (quality) + no second-stage accelerator ›Upstream dogleg dipole will filter out low-energy tail. May be “considerable” (~10 W/m)? ›Accidental beam failures: passive machine protection ›HEBT collimators cannot provide global protection Proposal: ›Remove HEBT collimators from the ESS baseline ›Design. Build if found necessary (latency!) ›Pursue the issue with the upstream dipole 26

27. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET EXTRA SLIDES 27

28. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET E2E Error Magnitudes 28 HB2014, MOPAB18 RFQ beam errors Element errors

29. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET BEAM STUDIES MEBT Scraper System? 29

30. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET 30

31. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET 71 ms failure in QP6 31

32. HEINE DØLRATH THOMSEN ESS TAC, 5-6 Nov, 2014 AARHUS UNIVERSITET 71 ms failure in QP6 32

33. 33Managed by UT-Battelle for the U.S. Department of Energy M. Plum – ESS Beam Losses and Collimation wkshp May 2014 Some sample H + beam profiles in the SNS HEBT Horizontal Vertical Profiles measured Dec. 22, 2013 Non-Gaussian tails / halo appear beginning at ~1/10 of peak Solid lines show Gaussian fits to the data 1/10

34. 34Managed by UT-Battelle for the U.S. Department of Energy M. Plum – ESS Beam Losses and Collimation wkshp May 2014 More H + beam profiles in the SNS HEBT Horizontal Vertical Profiles measured April 6, 2014 Non-Gaussian tails / halo appear beginning at ~1/10 of peak Solid lines show Gaussian fits to the data 1/10