1. Laser Stripping for H - Injection Wolfgang Bartmann ATS Seminar, 23-Jan-2014

2. Outline Introduction to multiturn injection Motivation for H - injection Principles of H- injection with foil – Required hardware – Limits – Machines with different parameters Laser stripping as alternative – Principles – Laser requirements – Implications for lattice and optics – Challenges – Status References 23-Jan-2014CERN Seminar, Laser Stripping2

3. For hadrons the beam density at injection can be limited either by space charge effects or by the injector capacity If we cannot increase charge density, we can sometimes fill the horizontal phase space to increase overall injected intensity. – Condition that the acceptance of receiving machine is larger than the delivered beam emittance 23-Jan-2014CERN Seminar, Laser Stripping3 Multi-turn injection for hadrons

4. Septum magnet No kicker Bump amplitude decreases and inject a new bunch at each turn Phase-space “painting” Closed orbit bumpers Varying amplitude bump 23-Jan-2014CERN Seminar, Laser Stripping4

5. Multi-turn injection for hadrons Turn 1 Septum Example: CERN PSB injection, fractional tune Qh = 0.25 Beam rotates  /2 per turn in phase space Example: CERN PSB injection, fractional tune Qh = 0.25 Beam rotates  /2 per turn in phase space On each turn inject a new batch and reduce the bump amplitude 23-Jan-2014CERN Seminar, Laser Stripping5

6. Multi-turn injection for hadrons Turn 2 23-Jan-2014CERN Seminar, Laser Stripping6

7. Multi-turn injection for hadrons Turn 3 23-Jan-2014CERN Seminar, Laser Stripping7

8. Multi-turn injection for hadrons Turn 4 23-Jan-2014CERN Seminar, Laser Stripping8

9. Multi-turn injection for hadrons Turn 5 23-Jan-2014CERN Seminar, Laser Stripping9

10. Multi-turn injection for hadrons Turn 6 23-Jan-2014CERN Seminar, Laser Stripping10

11. Multi-turn injection for hadrons Turn 7 23-Jan-2014CERN Seminar, Laser Stripping11

12. Multi-turn injection for hadrons Turn 8 23-Jan-2014CERN Seminar, Laser Stripping12

13. Multi-turn injection for hadrons Turn 9 23-Jan-2014CERN Seminar, Laser Stripping13

14. Multi-turn injection for hadrons Turn 10 23-Jan-2014CERN Seminar, Laser Stripping14

15. Multi-turn injection for hadrons Turn 11 23-Jan-2014CERN Seminar, Laser Stripping15

16. Multi-turn injection for hadrons Turn 12 23-Jan-2014CERN Seminar, Laser Stripping16

17. Multi-turn injection for hadrons Turn 13 23-Jan-2014CERN Seminar, Laser Stripping17

18. Multi-turn injection for hadrons Turn 14 23-Jan-2014CERN Seminar, Laser Stripping18

19. Multi-turn injection for hadrons Turn 15 In reality filamentation occurs to produce a quasi-uniform beam Phase space has been “painted” 23-Jan-2014CERN Seminar, Laser Stripping19

20. Charge exchange H- injection Multiturn injection is essential to accumulate high intensity Disadvantages inherent in using an injection septum – Width of several mm reduces aperture – Beam losses from circulating beam hitting septum – Limits number of injected turns to 10-20 Charge-exchange injection provides elegant alternative – Possible to circumvent Liouville’s theorem, which says that emittance is conserved – Convert H - to p + using a thin stripping foil, allowing injection into the same phase space area 23-Jan-2014CERN Seminar, Laser Stripping20

21. H- injection foil stripping 24 m 26-Sept-2013CERN Laser Stripping, WS Fermilab21

22. H - injection painting Now we “overinject” onto the same phase space area already occupied by the circulating beam 23-Jan-2014CERN Seminar, Laser Stripping22

23. Foil stripping - HW Chicane and painting bumpers (~4 each) – Chicane: one of these septum like depending on geometry Stripping foil – Thin foil: Foil holder with exchange possibility – Thick Foil: convert unstripped H - and H 0 to protons to guide them into dedicated waste beam channel – Vacuum and radiation compatibility Waste beam handling – Internal dump (PSB) – Short line to external dump – Electron collector – Careful design of beam trajectories required due to different angles for H -,H 0 in chicane magnets – Machines with running H - injection suggest tracking studies of waste beams and a high number of diagnostic possibilities 23-Jan-2014CERN Seminar, Laser Stripping23

24. Problems with foils Foil damage Present machines on the high beam power frontier are approaching the limits of foils 23-Jan-2014CERN Seminar, Laser Stripping24 Sarah Cousineau, Laser stripping WS, Fermilab, 26-27 Sept-2013 Sarah Cousineau, Laser stripping WS, Fermilab, 26-27 Sept-2013

25. Problems with foils Beam loss and radiation – Beam loss due to foil scattering (foil is highest loss point in SNS accelerator complex) Emittance growth due to foil scattering – Relevant for multi-purpose machines Laser stripping avoids a mechanical interaction with the beam 23-Jan-2014CERN Seminar, Laser Stripping25

26. Comparison of machine parameters …where laser stripping is considered (except for ISIS) – likely not complete ParameterUnitsISISSNSHP-PSFNALESS accumulator Kinetic energy at inj[GeV]0.81482 Beam power at inj[MW]0.161.2 - 30.190.345 Repetition rate[Hz]506011014 Total beam intensity2.5e131.25-3.1e142.5e142.7e132.8e14 (x 4) # injected turns150 - 2001100600360650 Macropulse lengthms0.21240.73 (x 4) Microbunch structureMHz202.5402.5352162.5704.42 Motivation for laser stripping Loss control, radiation Loss control, radiation, em growth Loss control, radiation 23-Jan-2014CERN Seminar, Laser Stripping26

27. Include laser into injection setup 23-Jan-2014CERN Seminar, Laser Stripping27 Wiggler or laser for neutralisation Laser for excitation Dedicated design of D3

28. Laser stripping concept: H - to H 0 Either Lorentz-stripping in a wiggler magnet… or Photo-dissociation 23-Jan-2014CERN Seminar, Laser Stripping28

29. Lorentz stripping 23-Jan-2014CERN Seminar, Laser Stripping29

30. H - neutralisation: Wiggler Magnet with ∫B·dl = 0  Lorentz stripping Vertical  no extra horizontal angular spread which would increase the laser power HP-PS: at least 0.6 T to keep emittance growth small Integration could be an issue 23-Jan-2014CERN Seminar, Laser Stripping30

31. H - neutralisation: Laser No emittance growth Easier integration than wiggler? Numerical calculation of neutralisation degree Laser micro pulse energy required for 99% neutralisation: 60mJ per micropulse -with factor 1000 reduction from recycling -f RF =352MHz and T inj =2ms gives 42 J per macropulse 23-Jan-2014CERN Seminar, Laser Stripping31 Demanding for the laser (and vacuum window)

32. H- neutralisation: Laser Feshbach resonance as alternative? Feshbach resonance appears at 113.49 nm (10.93 eV) in the H- photodissociation spectrum HP-PS: – With 1064 nm laser accessible with intersection angle of 37° – To reach 99% neutralisation (crosssection~1.39e-15 cm 2 ) a laser micropulse energy of 190 uJ is required – However: Δλ/λ~5.2e-6 while beam Doppler spread ~2e-3 – Need another factor 5e2 for full beam neutralization, leads to a laser micropulse energy of 73 mJ 23-Jan-2014CERN Seminar, Laser Stripping32

33. H - neutralisation: Laser n=2 shape resonance as alternative? 23-Jan-2014CERN Seminar, Laser Stripping33

34. H 0 --> p + stripping Doppler shift of laser frequency HP-PS: 1064 nm laser n=2 can be reached with 47.5° between ion beam and laser n=3 with 8.39 ° 23-Jan-2014CERN Seminar, Laser Stripping34

35. H 0 --> p + stripping divergent laser beam Scheme developed and tested at SNS (Danilov et al.): Resonant excitation of ground-state H 0 in field free region Stripping of excited electron in magnetic field Large spread of effective resonance frequencies  divergent beam Scheme developed and tested at SNS (Danilov et al.): Resonant excitation of ground-state H 0 in field free region Stripping of excited electron in magnetic field Large spread of effective resonance frequencies  divergent beam 23-Jan-2014CERN Seminar, Laser Stripping35 H-H- Divergent laser light

36. H 0 --> p + stripping divergent laser beam Using this scheme for HP-PS: Excitation to n=2 or n=3: 360 and 92 uJ laser micropulse energy This leads to > 20 MW laser peak power! Spontaneous decay reduces the efficiency: 1.7% of n=3 decay in 25 cm drift between laser interaction and stripping point 23-Jan-2014CERN Seminar, Laser Stripping36 Using a divergent beam to compensate the doppler broadening of the transition affects strongly the required laser power How to reduce laser power (Danilov et al., Future prospects for laser stripping): -Locking between laser and beam temporal structure -Dispersion tailoring -Photon recycling -Bunch length minimisation -Vertical beam size minimisation -Beam angular spread minimisation How to reduce laser power (Danilov et al., Future prospects for laser stripping): -Locking between laser and beam temporal structure -Dispersion tailoring -Photon recycling -Bunch length minimisation -Vertical beam size minimisation -Beam angular spread minimisation

37. Dispersion tailoring 23-Jan-2014CERN Seminar, Laser Stripping37 Interesting option if D’ can be accomodated in optics design of injection region

38. Dedicated design of stripping magnet Fringe field stripping – emittance growth Lifetime in magnetic field depends on quantum state, B-field and ion momentum Lifetimes of 4 GeV H 0* in dependence of B and a simulated fringe field numerically integrated to get rms angle error and hence emittance growth n=3 gives Δε of 2 – 4 um for B = 1 T Careful fringe field design needed! Normalised emittance growth for different H 0* quantum states as a function of peak magnetic field 23-Jan-2014CERN Seminar, Laser Stripping38

39. Stark broadening Stark effect: charged particle in an electric field  transitions will be broadened Overcome Doppler broadening by placing interaction region in a magnetic field  large Stark-broadening of transition Single frequency can excite the resonance for all atoms Stimulated emission suppressed HP-PS: – To reach Doppler width of 2e-3 need 0.3 T for n=3 transition – Lifetime of H 0* only 1e-10 s – Required laser micropulse energy slightly higher than previous method – Excitation takes place over ~0.5 m which introduces a large angle between injected and circulating protons  difficult integration Stark-broadening of quantum levels vs B-field for 4 GeV H 0 23-Jan-2014CERN Seminar, Laser Stripping39

40. Laser characteristics for HP-PS (H 0 --> p + stripping) Parametern=2n=3 Wavelengthnm1064 Laser/H- angledeg47.508.39 Angular spreaddeg±0.10±0.42 Micropulse energyuJ36092 Macropulse lengthms22 Macropulse energyJ25365 Peak power (single pass) * 3 (margin)MW21.65.5 Average power (single pass)kW43.211.0 Average power (mode-locking)W760193 Average power (Q=100)W432110 Vertical laser beam height (1 σ rms)mm1.5 Linac pulse, 1 σ rms separated by 2.84 nsps15 Laser repetition rate (max)Hz11 Availability%99 23-Jan-2014CERN Seminar, Laser Stripping40 Relevant parameters as input for laser feasibility discussion

41. Laser stripping - HW Chicane and painting bumpers (~4 each) – Chicane: one of these septum like depending on geometry and specially designed stripping magnet Stripping foil – Thin foil: Foil holder with exchange possibility – Thick Foil: convert unstripped H- and H0 to protons to guide them into dedicated waste beam channel – Vacuum and radiation compatibility Waste beam handling – Internal dump (PSB) – Short line to external dump – Electron collector – Careful design of beam trajectories required due to different angles for H-,H0 in chicane magnets – Machines with running H- injection suggest tracking studies of waste beams and a high number of diagnostic possibilities Laser – Wiggler magnet or laser for H - neutralisation – Laser for excitation + optical resonator – All the equipment to run the laser (optical table, fiber,…) – Vacuum window 23-Jan-2014CERN Seminar, Laser Stripping41

42. Implications for beam, lattice and optics 23-Jan-2014CERN Seminar, Laser Stripping42

43. Laser – Laser peak power is proportional to vertical injected beam size if the beam- laser interaction is horizontal Minimize as much as possible vertical beam size in IR  triplet structure in LSS for FNAL and CERN studies – D’ at interaction point to eliminate Doppler broadening – Longitudinal painting: large momentum range increases tremendously the required laser power – Bunch length: increases laser average power – Energy jitter: increases frequencies to be swept should be an order of magnitude lower than initial dp/p – Trajectory jitter Implications for beam, lattice and optics

44. Injection area optics Contradicting requirements for foil and laser  two different optics settings 23-Jan-2014CERN Seminar, Laser Stripping44 Foil optics Laser optics

45. Combined chicane for foil and laser 23-Jan-2014CERN Seminar, Laser Stripping45 Foil 1 Foil 2 Waste beam p+p+ B=1.6 T B ≤ 0.13 T Stripping of first e - H-H- H0H0 Laser

46. Items which deserve attention Laser – Locking to beam temporal structure – Optical resonator – Transport of laser light, radiation hardness 300 J through a vacuum window Integration of wiggler and laser with variable interaction angle Magnet design of wiggler and stripping chicane magnet (fringe field) Combination of foil and laser system, 3- and 4- magnet bumps with dispersion closed 23-Jan-2014CERN Seminar, Laser Stripping46

47. Summary High-intensity/brightness  H - injection H - injection for high beam power – Challenges with foils: damage, losses, radiation, emittance growth Laser stripping avoids mechanical interaction with beam – H - neutralisation: Lorentz-stripping in wiggler magnet or Photo-dissociation with laser (resonances) – H 0 to p + : excite ions on resonance and use the therefore higher probability of Lorentz-stripping in a chicane magnet Challenges: – Commercial lasers don’t fully match yet the requirements from accelerators but this community is extremely fast evolving – Wiggler design/integration – Fringe field design of stripping chicane magnet – Vacuum windows withstanding laser power 23-Jan-2014CERN Seminar, Laser Stripping47

48. Status quo of laser stripping At present – R&D phase – Proof of principle at SNS demonstrated 90% stripping efficiency for ~7 ns (see V. Danilov et al., PRST) Midterm: – 3-year experiment at SNS started with the aim of more than 90% stripping for 10 us (see talk S. Cousineau at FNAL workshop) – Requires a photon recycling optical cavity (see talk M. Notcutt at FNAL workshop) – Final experiment foreseen for Jan-2016 Longterm – Laser stripping to be operational with similar or better performance than foil stripping … 2020-2025 ??? 23-Jan-2014CERN Seminar, Laser Stripping48

49. References V. Danilov et. al., Physical Review Special Topics – Accelerators and Beams 6, 053501 V. Danilov, Future prospects for laser stripping in high intensity machines B. Goddard, Injection and Extraction, CAS slides B. Goddard et al., Laser Stripping for the PS2 Charge-Exchange Injection System, PAC09 S. Cousineau, SNS Laser Stripping, FNAL workshop, see below I. Yamane et al., POP experiment of Laser Stripping via a Broad Stark State Using BNL 200 MeV H- beam, ICFA-HB2004 D. Johnson, Conceptual Design Report of 8 GeV H- Transport and Injection for the Fermilab Proton Driver W. Bartmann et al., Laser stripping for CERN HP-PS, FNAL workshop, see below W. Bartmann, B. Goddard, H-Injection into PS2 and Laser Stripping, SNS workshop, see below H. Schönauer, ESS accumulator parameters Laser stripping workshop 2013 at FNAL: https://indico.fnal.gov/conferenceOtherViews.py?view=standard&confId=6855 https://indico.fnal.gov/conferenceOtherViews.py?view=standard&confId=6855 Laser stripping workshop 2009 at SNS: http://wiki.ornl.gov/events/lahbsa/default.aspx http://wiki.ornl.gov/events/lahbsa/default.aspx 23-Jan-2014CERN Seminar, Laser Stripping49 Thank you!