Extraction and beam delivery Christoph Hessler Bruno Balhan

Extraction and beam delivery Christoph Hessler, Bruno Balhan, Jeremie Bauche, Jan Borburgh, Brennan Goddard, Matthew Fraser, Verena Kain, Philipp Schicho, Linda Stoel, Carmen Tenholt, Francesco Velotti 7 th June 2017 11 th SHi. P Collaboration Meeting, CERN

Outline • Beam parameters • Beam loss, activation and personnel dose mitigation • Transfer line design status • Splitter magnet • Dilution system • Conclusion 2

Outline • Beam parameters • Beam loss, activation and personnel dose mitigation • Transfer line design status • Splitter magnet • Dilution system • Conclusion 3

Beam parameters Parameter Unit Extraction energy Ge. V Bunch intensity 1010 p/b SPS-FT North 400 ~400 1. 07 Number of bunches per batch Bunch spacing SPS-FT SHi. P Must be different from NA beam by at least 5 Ge. V for machine protection reasons. Exact energy TBD. 4200 ns 5 Number of train per batch 2 Train spacing ns 1100 Train length ns 10500 Momentum spread 10 -3 ± 1. 5 (uniform distribution) Emittance H (norm. ) µm 8. 0 Emittance V (norm. ) µm 5. 0 Total intensity per batch 1013 p 5. 88 4. 49 Spill length s 9. 7 1. 0 Cycle length s 26. 4 7. 2 4

Outline • Beam parameters • Beam loss, activation and personnel dose mitigation • Transfer line design status • Splitter magnet • Dilution system • Conclusion 5

SHi. P needs a factor ~4 more protons per year than presently delivered to NA • Limited by beamloss and activation in SPS LSS 2 extraction channel • Already at 10 m. Sv/h remnant dose 2012 6

Promising mitigation measures being studied • Improve SPS reproducibility and magnetic stability (reference magnets) • Dynamic extraction bump to overlap different momentum separatrices • Passive diffuser to scatter beam away from septum wires • Bent crystal to coherently bend beam away from septum wires • Non-linear lenses to reduce particle density at septum wires • Improved absolute beamloss level measurement • Low-Z septum wires and low activation anode and vacuum tank materials • Improved remote handling • Online modelling of induced activation build-up and decay M. A. Fraser et al. , SPS Slow Extraction Losses and Activation: Challenges and Possibilities for Improvement, Proc. IPAC’ 17, MOPIK 045 7

Improved SPS reproducibility and stability • Machine reproducibility dominated by hysteresis effects, affects spill • New B-train being deployed for online measurement of reference magnets LHC in cycle super- Date V. Kain et al. , SPS Slow Extracted Spill Quality During the 2016 Run, Proc. IPAC’ 17, MOPIK 049 8

Dynamic bump to overlap separatrices • Routinely used at J-PARC main ring, direct gain of 20% possible in SPS • Required pre-cursor for more advanced loss reduction ideas • To be tested in MD in 2017 without dynamic bump: with dynamic bump: 9

Passive diffuser (scatterer) • • Old idea already in use at CERN in PS septum for CT extraction to SPS Studies show x 2 improvement in losses with 3 mm of W/Re wire Prototype designed, planned installation YETS at end 2017 MD tests in 2018 Diffuser wires B. Goddard et al. , The Use of a Passive Scatterer for SPS Slow Extraction Beam Loss Reduction, Proc. IPAC’ 17, MOPIK 044 10

Bent crystal to shadow septum wires • “Active” diffuser, deflects beam instead of scattering • Make use of bent crystal features, as already tested in SPS by UA 9 • Factor 4 loss reduction found in simulation M. A. Fraser et al. , Experimental Results of Crystal-Assisted Slow Extraction at the SPS, Proc. IPAC’ 17, MOPIK 048 Curtesy UA 9 experiment F. M. Velotti et al. , Reduction of Resonant Slow Extraction Losses with Shadowing of Septum Wires by a Bent Crystal, Proc. IPAC’ 17, MOPIK 050 11

Non linear lenses to reduce p density at septum • Investigating additional (strong) decapoles in SPS to fold separatrices • Simulate factor 1. 3 loss reduction if separatrix density is linearised • Factor 2 loss reduction if separatrix is folded L. S. Stoel et al. , Phase Space Folding Studies for Beam Loss Reduction During Resonant Slow Extraction at the CERN SPS, Proc. IPAC’ 17, MOPIK 046 12

Improved absolute beamloss level measurement • Cross-calibration of TT 20 SEM (BSI) measurement with BCT and BLMs • Absolution calibration of SEM in TT 10 with known intensity 13

Low-Z septum wires and low activation anode and vacuum tank materials • Low-Z septum wires being investigated (carbon nanotubes). C wires alone give a factor ~1. 5 reduction in losses. • C wires combined with passive W/Re diffuser gives factor ~2. 8 loss reduction • Ti and Al investigated for tank material – Al gives best results for short- and long-term activation, and waste disposal. Could hope for a factor 2 -3 activation reduction from present St. St vacuum tanks (need to evaluate overall impact) 14

Improved remote handling and exchange procedure • Remote controlled transport vehicle for septum exchange used for the first time in 2015/16 Technical Stop • Factor ~2 reduction obtained in collective dose 15

Online modelling of induced activation build-up and decay • Empirical model first conceived during WANF operation was revived and fitted to logged data: with • Included extracted proton intensity and normlaised losses: • Good agreement, permitted first estimates of activation rates during SHi. P confirming factor of 4 improvements required and fist estimates of cool-down times IR model (blue) fitted to measured data (red) on ionisation chambers located in the LSS 2 extraction straight M. A. Fraser et al. , Modelling the radioactivity induced by slow-extraction losses in the CERN SPS, paper TUPIK 086, IPAC’ 17, 16 Copenhagen, Denmark

Outline • Beam parameters • Beam loss, activation and personnel dose mitigation • Transfer line design status • Splitter magnet • Dilution system • Conclusion 17

Transfer line location • New beam line branches off TT 20 transfer line at splitter 1 Target coordinates (CCS) • Total length incl. TT 20: ~1 km X (m) 652. 236651 Y (m) 4713. 196543 Z (m) 2441. 820322 bearing (rad) -0. 032111639 slope (rad) 0. 000246327 18

Transfer line optics • FODO lattice • Beam radius (1 s) at target: 8 mm • Dispersion suppressed at target Existing part SPS extraction point Splitter Vertical bending magnets Target Horizontal bending magnets New part Existing part New part 19

Transfer line aperture • 6 s beam envelope incl. 5 mm orbit deviation and 10% beta beating • Total momentum spread in spill very large, but correlated with the temporal position in the spill. Magnet powering is changed during spill to compensate dp/p change. → Lower dp/p = 7. 5 e-4 has been assumed for aperture calculation 20

Transfer line magnets • Magnets required for the new part: Quantity Type Function 6 QTL Quadrupole 5 MBB Main bend 18 MBN Main bend 3 MSSB like (new to design) Splitter 2 MPLS Horizontal diluter 2 MPLV Vertical diluter TBD Correctors • Magnet types have been selected according to their availability. • MPLS/V bumper magnets are not in stock and have to be built new or other suitable types have to be found. 21

Outline • Beam parameters • Beam loss, activation and personnel dose mitigation • Transfer line design status • Splitter magnet • Dilution system • Conclusion 22

Design and powering requirements for the new splitter magnet Parameter Existing MSSB splitter New MSSB splitter Unit Comment Number of magnets 3 (+1 spare) Physical yoke length 5190 mm Integrated field 3. 99 Tm Gap field 0. 8 T Vertical aperture 75 (full beam) 75 (+ septum height for mm non deflected beam) Horizontal aperture -20 / +190 ± 90 mm Presently asymmetric position of septum hole w. r. t. pole axis Switching time DC operation 2 s From +v to –v polarity at full field Flat top length Continuous 9. 7 (NEA) / 1 (SHIP) s Energy saving since OFF when no beam At 400 Ge. V/c 23

Existing splitter vs. new splitter design • Due to the beam line geometry, the polarity must be switched between NEA beams and SHIP beams. A polarity change in the 1 -2 Hz time scale is not compatible with the present solid iron yoke. It needs to be laminated to mitigate Eddy currents. • The needed pole width is governed by the deflection length + beam size + pole overhang (depending on the optimization of the pole edge) • The existing MSSB splitter has been originally designed for the NEA and the WEA with an asymmetric position of the septum hole at the border of the good field region (GFR) as to benefit of the needed field quality over the full deflection. For the NEA, the deflection is however smaller than was for the WEA, so the pole overhang is larger than needed. • For the new splitter, the deflection is however doubled w. r. t the NEA beam deflection with an equal deflection angle for the SHIP beam. 24

Proposed cross section • Former MSSB • Pole width: 400 mm • Weight: 24 tons 155 mm • New MSSB • Pole width: 310 mm (needed GFR 180 mm) • Weight: 21 tons 285 mm 115 mm 25

Magnetic 3 D design 26

Outline • Beam parameters • Beam loss, activation and personnel dose mitigation • Transfer line design status • Splitter magnet • Dilution system • Conclusion 27

Dilution system • To not exceed the damage threshold of the target a dilution system is required to sweep the beam over a large target area during the spill. • Sweep parameter (baseline): Parameter Value Pattern Circle Sweep radius 50 mm Number of turns per spill 4 Spill duration 1 s Beam radius (1 s) 8 mm Diluter rise time 62. 5 ms • Dilution system: 2 MPLS (horizontal) and 2 MPLV (vertical) ~100 m upstream of target • Powering function: 28

Conclusions (loss, activation and dose mitigation) • Factor 4 more protons extracted through LSS 2 remains a challenging target, with no single magic bullet • Machine stability and dynamic bump control are pre-requisites • Assuming this, several options being perused which show factor 2 -4 reduction – will need eventually to focus on most promising (which might be most operationally robust) • Activation reduction and dose reduction will need to make up the remaining factor (~2) in personnel dose, by materials, remote intervention and personnel training/procedures • Improvements in measurement and monitoring also mandatory, in progress • Strong synergy with present SPS and slow extraction operation, as already limiting protons to NA 29

Conclusion (Transfer line, splitter, dilution system) • Beam line optics solution for 8 mm beam size at target has been developed. • 6 s beam envelope fits into the aperture. • A design of a more compact, laminated splitter magnet type is in work. • A possible layout of a dilution system capable to achieve a sweep radius of 50 mm on the target has been identified. • More work needs to be done, e. g. on beam instrumentation, power converters, vacuum system, failure scenarios … 30