AARHUS UNIVERSITET ESS TAC 5 6 Nov 2014

AARHUS UNIVERSITET ESS TAC, 5 -6 Nov, 2014 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) p. RÆSEN TATION 1

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

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

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 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 Ge. V › 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

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 R. Bruce, 2014. 04. 15

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

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

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

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 ESS (5 MW, p) vs. SNS (1. 4 MW, H-)? H -, I p 2 H- p p, Ip Shishlo et al. , IPAC'12, TUOBA 03 (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

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

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 Simulating the HEBT Halo? Injection @ HEBT s = 0 › Two-component beam, (core + halo) › › Typically 2 x Gaussians εh / ε c = 5 Nh / (Nh+Nc) = 1% 6 D: transverse + longitudinal End-to-End, ESS Acc. Phys. › 4 D 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

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 Injection: HEBT Error Studies IPAC’ 14, WEPRO 074: • 1000 HEBTs x 106 particles: STAT (+ corr) + DYN Er • No losses until target monolith (<100 W) 12

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 End-to-End (ESS Beam Physics Group) HEBT: › Low-energy protons (300 -600 Me. V) › E < 800 Me. V are lost inside the first dipole R. Miyamoto, HB 2014, MOPAB 18 -Errors 1 x 107 RFQ output +Errors 103 x 105 13

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

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 “Alternative”: Normalized HEBT Aperture APT HEBT: 80 @ 100 MW SNS HEBT: 15 – 24 @ 1. 4 MW 15

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

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

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

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 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 τf of the initiating event is important in order to determine response time of mitigating system. › FAST: τf < 2. 86 ms, beam parameters can change considerable during a pulse › RF (arcing) › Low-inductance magnets (raster system? ) › MODERATE: τf > 2. 86 ms, impact can build up over a number of pulses › High-inductance magnets (conventional magnets) 19

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 Case 1: RF Failure, ∆E = 0 Me. V ∆y < 0. 33 mm/Me. V 20

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 Case 1: RF Failure, ∆E = -100 Me. V ∆y < 0. 33 mm/Me. V 21

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

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

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

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

AARHUS UNIVERSITET HEINE DØLRATH THOMSEN ESS TAC, 5 -6 Nov, 2014 E 2 E Error Magnitudes RFQ beam errors Element errors HB 2014, MOPAB 18 28

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

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

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

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

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

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