1. Laser Stripping and H 0 monitor systems 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI1

2. Outline Motivation SNS Laser wire beam profile system Adaptation to LINAC4 parameters H 0 detection Outlook 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 2

3. Motivation Emittance measurement required at 160 MeV A Slit&Grid system (as in LINAC2 ) not suitable for higher energy. – High thermal load – Slit thickness > 15 cm => Complex slit geometry Possibility of using a laser wire Can measure full beam power Non destructive measurement No space charge effect Can go to higher intensity, energy, repetition rate Can achieve high resolution and accuracy 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 3

4. Principle of beam profile and emittance measurement with Laser Wire If the laser station is positioned before a dipole magnet, emittance and profile measurement can be done at the same time 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI4 Profile measurement Emittance measurement Stripping

5. SNS Laser wire beam profile system Used in the Superconducting part of the LINAC for profile measurement. Stripped electron are detected by a faraday cup. Q ‐ Switched Nd:YAG laser (commercial type): 30 Hz repetition rate Maximum energy 1 J 10 ns beam pulse Wavelength 1064 nm 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 5

6. SNS Laser wire beam profile system (* ) 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Profiles of H- beam along the SCL measured during 2010. The measurement was conducted on full power (1 MW) neutron production beam(*). (beam sizes from 0.9 to 3.5 mm) * LASER BASED DIAGNOSTICS FOR MEASURING H- BEAM PARAMETERS Y.Liu et al. (PAC 2011 Proceedings WEOCN1) 6 Measured emittance: ~ 0.2 mm ⋅ mrad 200 MeV 1 GeV

7. SNS Laser wire beam profile system (* ) 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI * LASER BASED DIAGNOSTICS FOR MEASURING H- BEAM PARAMETERS Y.Liu et al. (PAC 2011 Proceedings WEOCN1) 7 Beam power is not reduced => no effect on SNS Neutron production.

8. Adaptation to LINAC4 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Photoneutralization Cross section Proposal : use similar Nd:YAG laser in LINAC4 Wavelength in the laboratory frame 1064 nm In the beam rest frame, the photon energy is: E gamma =1.6 eV i.e a wavelength of 780 nm With Lorentz boost at 160 MeV and θ L =90° At 160 MeV the cross section is close to the maximum => should use a Laser with similar wavelength 8

9. Adaptation to LINAC4 SNS beam vs. LINAC4 beam Energy LINAC4 < SNS => Higher photo neutralization cross section Bunch length LINAC4 > SNS => Saturation effects lower => LINAC4 beam parameters less critical =>The system can be used with better stripping efficiency 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 9

10. LINAC4 case During the acceleration along the linac and the transfer to the PS booster, the second electron can be stripped from black body radiation, magnetic field and residual gas. neutral beam can reach the H 0 detector and perturb the measurement. Simulations have been done to estimate the background 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Background from the linac removed by dipole 1 Losses depends on the energy => Constant energy => Loss rate constant Simulations done in order to check the feasibility of the system. 10 Possible implementation of emittance measurement (Old TL design)

11. LINAC4 case-background 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Proccess Probability of loss per meter Black Body radiationneg. Magnetic field1.10E-05 rest gas6.50E-07 If laser beam size around 100 μm and assuming a full stripping => number of stripped particles ~10 7 Background and signal comparable if gating the detector over the all linac pulse. Drift length [m] Number of particles 146.87E+08 0.55.80E+07 0.34.59E+07 0.23.94E+07 11

12. If we assume that the probability of stripping by residual gas interaction or magnetic field stripping is independent of time, the background particles are generated over a pulse, i.e 400 μs. For the signal, the particles are generated over a laser pulse, i.e. 10 ns. By gating the signal with a short time window, the background effect can be reduced. Assuming a window of 20 ns, the number of background particles can be reduced by a factor 20000 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI LINAC4 case-Background Drift length [m]Number of particles 143.44E+04 0.52.90E+03 0.32.30E+03 0.21.97E+03 12

13. H 0 detector H 0 detector must have a fast time response. must also have a good resolution and good signal/noise ratio The number of particles is low 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI microstrip Silicon or Diamond detector Radiation hardness detectorSilicondiamond Radiation hardness [p/cm2]10^1210^1510^17 lifetime0.5 h152 days42 years 13 Silicon can not be used for this application

14. Diamond detectors A Diamond detector is more suitable than Silicon – Can detect single particles (sensitive) – Collection times ~10ns(fast) – Up to 10 17 MIPs/cm 2 (rad-hard) Need to investigate the possibility of using a segmented pCVD diamond detector for profile measurement 10/18/201114B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI

15. Main questions Are diamond substrates sufficiently uniform? Is the metallization of the different channels reproducible (junctions formation etc.)? Is the ageing effect sufficiently small to allow a long life? What is the effect of sustained radiation dose? 10/18/201115 B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI

16. R&D with CIVIDEC A contract with CIVIDEC has been signed – CIVIDEC will provide a 20x20x0.5 mm 3 pCVD diamond detector with 5 readout strips on one side and a common BIAS plane on the other – CIVIDEC will provide 5 analog fast front end amplifiers (40 dB 2GHz) 10/18/201116B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI CERN will have to provide the counting/sampling electronics with the corresponding software

17. R&D with CIVIDEC 10/18/201117B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI

18. Outlook Emittance measurement based on laser stripping. Parasitic measurement Flexibility No interaction between H - beam and matter Profile measurement with the full beam intensity Cost Development of H 0 detector Background (can be reduce with fast electronic) 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI NEXT The background in the new transfer line should be calculate with more accuracy Use precise beam parameters to determine the resolution of detector. Beam test with Diamond detector provided by CIVIDEC Laser test in the 3 MeV test stand 18

19. Outlook Integration and test in the transfer line: Without an intermediate dump in TL: » No separation of H 0 and H - => no H 0 detector test (can be done with over beam) » 1 laser station can be installed after the PIMS: Commissioning and test of the laser station Stripping efficiency test Profile measurement with full LINAC4 Power. With an intermediate dump in TL: » Installation of a laser station after a dipole » Test of the full system 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 19

20. EXTRA SLIDES 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 20

21. SNS LASER System 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 21

22. LINAC4 case-background issues Spectral density of thermal photon calculated with Planck formula. 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Doppler shift applied for the energy spectrum in the bean rest frame Stripping by black body radiation is negligible Black body radiation 22

23. LINAC4 case-background issues Spectral density of thermal photon calculated with Planck formula. 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Doppler shift applied for the energy spectrum in the bean rest frame Stripping by black body radiation is negligible Black body radiation 23

24. LINAC4 case-background issues For β=0.52, B=1T, and a distance in a magnetic field of 1 m, the stripping probability is 1.1.10 -5 For the background particles reaching the detector, the path in Magnetic field is less than the length of the dipole Assuming a target of 4*4 cm, 2 meter downstream the dipole exit, and a perfect magnetic field and trajectory, the path is 15 cm 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Magnetic field stripping. Ions lifetime in a magnetic field Probability of stripping 24

25. LINAC4 case-background issues The probability of stripping is given by : 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Residual gas stripping With λ the mean free path The stripping cross section depends on the beam energy. Measurements are available in the literature at 400 and 800 MeV. The stripping cross section in N 2 gas has been scaled and used for the calculation. The stripping probability per meter is: 6.5.10 -7 25

26. Possible tests at the 3 MeV diagnostic bench Slit tank is equipped with a laser window: – Test of the stripping efficiency Use the full laser power to strip the beam (without focusing) Detect the current drop with BCT Measure current with H 0 /H - current monitor prototype (foreseen for PSB injection) 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI 26

27. H 0 detector-e - effect Error is less than 0.1% Nevertheless FLUKA only track electron above 1 keV Possible problem with these very low energy electrons 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Fluka simulations has been used to simulated the effect of the electron of the measurement, a simple geometry has been used (500 μm Diamond foil). Bragg curve of 90 keV electron in DiamondReconstructed profile 27

28. H 0 detector The range of 90 keV electron in Tungsten is around 10 μm. A stripping foil van be used as electron dump upstream a diamond detector. The effect on a proton beam of a 100 μm Tungsten foil has been simulated. Proton beam have no divergence and energy spread 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Distance [cm]01234510 error [%]0.010.7423.886.429.3630 Error on the beam profile increase with the distance. The detector can not be installed in Air. 28

29. H 0 detector Silicon diamond single crystal diamond polycrystal Band gap [eV] 1.15.47 Breakdown field [MV.cm -1 ] 0.310 Electron mobility [cm 2 V -1 s -1 ] 145045001800 Hole mobility [cm 2 V -1 s -1 ] 48038001000 Ionization energy [eV] 3.6213 10/18/2011B.Cheymol, E. Bravin, U. Raich, F. Roncarolo BE/BI Mobility is higher with diamond, no large difference between electron and hole Can use both for measurement Collection efficiency is higher with singe crystal (up to 100%). Efficiency of polycrystal has to be checked. Amplification in the detector: for every H 0 entering the detector 1.2.10 4 e-/hole pairs are created. Assuming 90% of collection efficiency signal in the order of hundredth of mA. Depending on the beamlet size and cost single crystal is a better solution. 29