1. ESSnuSB Open Meeting 26-27 May 2014 CERN E. Wildner J. Jonnerby, M. Martini, H. Schönauer 13/03/14EUROnuSB Lund, E. Wildner 2 W. Bartmann, E. Bouquerel, M.Dracos, T. Ekelöf, M. Lindroos, D. Mc Ginnis, M.Eshraqi J.-P. Koutchouk, N. Vassioupolus, G. Lanfranco, Y. Papafilippo, R. Ruber and others ESSnuSB Compressor Ring

2. ESS H- acceleration for neutrinos The ESS Linac will be built for neutron spallation (proton acceleration 14 Hz) Duty factor low (4%); some additional capacity is available Repetition rate can be increased to 28 Hz, to permit an extra acceleration cycle Neutrino option: acceleration of 5 MW H- H- acceleration must not perturb the neutron facility Modifications (upgrades) of the Linac must permit the doubling of power (5 + 5) MW AND requirements for the pulse compression 13/03/14 3 H- ? ? ? ? ESS Technical Design Report, April 23, 2013 ESS-doc-274 http://europeanspallationsource.se/documentation/tdr.pdf EUROnuSB Lund, E. Wildner

3. ESSnuSB Accumulator 13/03/14EUROnuSB Lund, E. Wildner 4 Neutrino beam ESS linac Neutron spallation target H-H- p Target/horn station Critical bend (Lorentz stripping) Switchyard Accumulator Preliminary ! No civil engineering expert work yet. τ H 1.5 μs τ 0 = 100 μs Horn current

4. Higher energies and the Layout 13/03/14EUROnuSB Lund, E. Wildner 5 Neutrino beam ESS linac Neutron spallation target H-H- p Preliminary ! Civil engineering to be taken into account! Target/horn station 2 GeV Achromat IF > 2 GeV Accelerating cavities

5. 13/03/14 EUROnuSB Lund, E. Wildner 6 ESS Accumulator for neutrinos Constraints on present neutrino target focusing system – The secondary beam has to be focused – Today’s focusing systems require beam pulses shorter 3 ms (cooling, power supplies etc.) Solution: reduce beam pulse length – Compress the linac pulse in an accumulator – The accumulator size should correspond a pulse length on target < 10  s Accumulator constraints – Reasonably-sized accumulator ring – Multiturn injection of p with high intensities becomes inefficient – Too high intensities in the ring may cause collective effects and beam loss – ESS has interest in an an accumulator as well: Synergies?

6. 13/03/14 EUROnuSB Lund, E. Wildner 7 Mitigate Difficulties with High Intensities Fraction the Linac pulse and stack the shorter pulses 1.In space: 4 accumulators, arXiv:1309.7022v3 or 2.In time: several pulses pass consecutively one accumulator charge exchange injection to limit multiturn losses: use H - - ions – Needs an extra ion source (space for it!) – Merging into linac at optimal position (after MEBT?) – Intrabeam Stripping and Lorentz stripping need to be evaluated (linac) – Radiation – Etc. H- ? ? ? ?

7. 13/03/14 EUROnuSB Lund, E. Wildner 8 4 Accumulators Technical design from EUROnu (2012) – 1 MW on each target, 4 targets – One accumulator – 2.5  s pulse length ESSnuSB – 1.25 MW on each target, 4 targets – Reasonable accumulator circumference of 430 m =>1.5  s pulse length – 1.1 10 15 p would give SC of -0.67 (round beam, 2.0 GeV, 100  mm mrad) – In each ring 1.1 10 15 /4 => 2.75 10 14 – In one ring: For 2.75 10 14 protons in machine SC < – 0.2 (acceptable) – Cf SNS, C = 220 m, 200  mm mrad, 2.0 10 14 protons, ….  Q=-0.3, Bf = 0.4 Bf N. Vassilopoulos

8. 13/03/14 EUROnuSB Lund, E. Wildner 9 One accumulator 4 Accelerators for accumulation seem costly and not necessary – One accumulator could pulse 4 times with ¼ of the linac pulse length The injection bumper is too slow – Rise time for the PS Booster bumpers is10 ms (same for the fall time) We propose to make 4 linac pulses of length 2.86/4 ms (same beam power) – They would be injected sequentially into accumulator – Spaced using timing such that bumpers are comfortable – However a price has to be payed… NB: accumulation for ESS neutrons need H- but considerably longer pulses at extraction from accumulator: this is not forgotten but is less straight forward, needs more design work

9. Linac Pulsing 70 Hz, present baseline 13/03/14EUROnuSB Lund, E. Wildner 10 35.7 ms 2.86 ms 28 Hz neutron neutrino 71.4 ms, 14 Hz 14.28 ms 0.7 ms 71.4 ms, 14 Hz 70 Hz 2.86 ms Four Accumulators One Accumulator (baseline)

10. 70 Hz linac pulsing 13/03/14EUROnuSB Lund, E. Wildner 11 Fill time of the superconducting cavities: For loaded Q, this is about 0.2 ms For two 3 ms beam pulses, this is 6.6% of the beam pulse length This corresponds to an inefficiency of 6.6% 4 pulses at 0.75 ms and one pulse of 3 ms: 5 x 0.2 ms = 1 ms filling time, 16.6% inefficiency (10% extra) Keep in mind: 4 rings are 4 times operation and maintenance cost, not less Can it be technically achieved (evaluation ongoing)? What about research on adapted cavity filling ? Foil heating in accumulator (see later) Communication D. Mc Ginnis

11. ESSnuSB Accumulator Lattice SNS C=376 m SNS straight section for injection used “as is” for simulations of foil stripping Less bending strength to ease energy upgrade No magnet considerations yet Collective effects not yet completed ESSnuSB Straight Arc C=278 m Circumference376 m Dipole field0.635 T # Dipoles64 # Quads84 Bending radius14.6 m Injection region12.5 m Revolution time1.32 μs J. Jonnerby

12. Multi-turn injection for hadrons Septum magnet No kicker Bump amplitude decreases and inject a new bunch at each turn Phase-space “painting” Closed orbit bumpers Varying amplitude bump

13. H- injection foil stripping 24 m Courtesy W. Bartmann

14. Injection area optics (foil/laser) Contradicting requirements for foil and laser  two different optics settings (however: the layout is the same!) 20/03/14ESSnuSB Uppsala, E. Wildner 15 Foil optics Laser optics Courtesy W. Bartmann

15. Foil stripping feasibility: first stage approach Simulations of MW accumulator projects have been done with the ACCSIM Code. The results are compared with the ORBIT results (courtesy M. Plum, J. Holmes) for representative SNS beams. Feasibility of Stripping foil injection H. Schönauer, CERN 13/03/14EUROnuSB Lund, E. Wildner 16

16. TEST CANDIDATE: ESS Linac + Exteded SNS Lattice CERN SPL PDAC 2001 1Foil CERN SPL PDAC 2001 2Foils SNS C [m]318943 242 T [GeV]22.2 1 P beam5 GW / 42 GW 1 GW f rep [Hz]70 / 1450 60 Np 2.8E14 2.3E14 1.5E14 N turns650850 1060  Norm (95%) 100 / 200  *)150  200   Linac (95%) 1.33  2  1.5  N macro 3300041000156000 Foil [  g/cm2] 750 2 x 750400 *) 100  too small; better 200  like in SNS Comparison of Foil Heating Simulations for some Project Lattices with the SNS 13/03/14EUROnuSB Lund, E. Wildner 17 H. Schönauer, CERN

17. 13/03/14EUROnuSB Lund, E. Wildner Comparison of Phase space Occupation for 100  vs. 200  normalized Emittance For an emittance of 100  the average Nr of foil hits of the circulating beam approximately doubles - the linac beam remains about the same Space Charge Detuning (approx.): -0.15 (100  ), -0.08 (200  ) 18 H. Schönauer, CERN

18. ESS Foil (Extended SNS Lattice): Peak Temperatures H- Linac H- Linac+ p circulating Maximum Foil Temperatures: 1797 K (H- Linac Beam)) 2050 K (H- + p circulating Beam) 13/03/14EUROnuSB Lund, E. Wildner 19 H. Schönauer, CERN

19. ESS stripping foil heating considerations I Table 1: ESS beam characteristics at injection 1.To keep constantly the foil temperature below 2500  K the pulse RMS spot size should be about 2 mm (x & y dir.) which needs betatron functions at accumulator ring injection close to 36m. 2.Protons and electrons in H - having the same velocity at foil entrance (same   &  ) the electron energy is then 1.09 MeV and its total stopping power is 1.61 MeV cm2/g. So the H - total stopping power is 4.98 MeV cm2/g. ParameterValue Ion kinetic energy 2 GeV (  = 3.1) H  pulse duration0.715 ms = 2.86 ms/4 H  pulse repetition rate70 Hz, 14.29 ms H  mean pulse current 62.5 mA RMS normalized emittances and preferred beam size  x,y  0.33  m &  x,y = 2 mm with at injection  x,y  36 m Carbon foil dimensions (x, y, z) Thickness area density 17  62 mm 2  3.9  m (t c [  m]) = 750  g/cm 2 H  total stopping power at 2 GeVS p = 4.98 MeV cm 2 /g M.Martini, CERN

20. ESS stripping foil heating considerations (2) M.Martini, CERN

21. ESS stripping foil heating considerations (3) 26/05/2012M. Martini ESSnuSB Meeting 26-27/5 22 Solution of the 3D heat equation with Mathematica for the ESS beam Fig. 1: Time evolution of the maximum carbon foil temperature at the pulse spot center derived from the 3D PDE (cont. line) and the simplified 1D ODE (dotted line). Both plots differ as the 1D model does not contain the heat conduction effect Fig. 2: Time evolution of the carbon foil temperature versus the foil height (y dir.). The temperature decreases quite rapidly along the y axis (as along the x axis) For the beam characteristics of Table 1, both figures show that the foil temperature modulation in the repetitive accumulator filling cycles is quasi stable after the second long cycle, each made of four 0.715 ms injection pulses (repeated every 14.29 ms) plus a 14.29 ms gap (empty injection cycle). Fig. 1 shows that the maximum stripping foil temperature varies between 1032  K and 2072  K M.Martini, CERN

22. Linac Pulsing, option if current too high ? 13/03/14EUROnuSB Lund, E. Wildner 23 35.7 ms 2.86 ms 28 Hz neutron neutrino 71.4 ms, 14 Hz 14.28 ms (0.7 * 2) ms, and half the intensity, for example (to mitigate high H- intensity) How would this option influence the linac ? 71.4 ms, 14 Hz 70 Hz 2.86 ms Four Accumulators One Accumulator Lower linac peak current

23. Extraction to 4 targets: Switch-yard 13/03/14EUROnuSB Lund, E. Wildner 24 E. Bouquerel Development for EUROSB ESSnuSB beam energy is lower Extraction timing is different (50 Hz -> 70 Hz) Needs ~ 100 ns gap in Accumulator Regular gaps in linac beam (chopping)

24. Work (-packages) for Accumulator CDR 13/03/14EUROnuSB Lund, E. Wildner 1.Accumulator design, extraction, collimation and beam dynamics 2.Laser stripping of H-, injection design and laser technology 3.Transfer lines (Lorentz’ stripping considered) and switch-yard update 4.Layout and civil engineering of accumulator and transfer lines a.Should be done with on-site expertise (local rules and guidelines) 5.Design work together with Linac experts to optimize the accumulator design (for example the linac pulsing and the beam current) 6.Estimation of radiation (mitigation) for safety, handling and equipment tolerances 7.Costing & safety (included elsewhere) 25

25. Summary 13/03/14EUROnuSB Lund, E. Wildner One accumulator: collaboration with ESS linac experts – Linac pulsing (and current changes) ? Lattice design: based on SNS used for simulations Laser stripping : 2025? CERN synergies ? Foil stripping solutions (necessary fallback): possible Need to select subjects out of work-list for the EU call Accumulator should be flexible (ESS neutrinos) 26