1. Crystal tests in AB/ATB/EA (previously SL-EA) H.W.Atherton,C.Biino, M.Clément, N.Doble, K.Elsener, L.Gatignon, P.Grafstrom, J.B.Jeanneret, U.Uggerhoj, In close collaboration with many others, in particular friends from Aarhus, CERN, Darmstadt, Dubna, Grenoble, Johannesburg, Strassburg, Stuttgart presented by L.Gatignon / AB-ATB-EA  Studies of proton channeling  Radiation hardness for protons  Studies of ion channeling  NA48 application

2. Incentive: Application of a bent crystal to provide simultaneous and collinear K S and K L beams for the NA48 CP-violation experiment Approach: Started cooperation with E.Uggerhoj and S.P.Moller and their NA43 colleagues to gain experience with bent crystals. Study performance and limitations of bent crystals Prepare the specific application for NA48 Investigate long-term stability – radiation hardness As the opportunity presented itself, some of these studies were extended to Pb and In beams

3. Few 10 12 ppp > Few 10 4 ppp

4. STUDIES WITH PROTON BEAMS Try to understand bending phenomenology Measure limits Work towards design of crystal holders Use mainly H8 beam Initial attempt: H8 microbeam, 450 GeV/c protons Horizontal divergence 3 microrad Spot size 2 H x 1 V mm 2 FWHM Intensity at the 10 4 – 10 6 level Silicon crystal, 10x50x0.9 mm 3 Front and back ends 3x8 mm 2 fully depleted solid state detectors Note: outgoing beam:   =2  p = 15  rad

5. to remove variation in R curv over length of crystal Ball bearings (“fluid”) ≈ 10% fully bent through 7 mrad Too much material (bkgd into detectors) Crystal deformation due to balls Non-uniform radius of curvature

8. 1992: Next H8 test Si crystal, 52x9x0.9 mm 3 Incident beam badly tuned: divergence 35  rad More uniform bending radius but curvature not monitored Causes “foot”

10. Bending efficiency:

11. 1993: Comparison of 450 and 200 GeV/c (110) Si crystal, 50x10x0.9 mm3 4 solid state detectors Classical 3-point bender

12. 450 GeV/c microbeam:

13. 450 GeV/c: microbeam (    = 3  rad) 200 GeV/c: secondary beam (larger   ) 3 mrad bend

14. Preliminary results for axial channeling:

15. In a  - (negative beam): Axial channeling: some clear deflection seen but no particles are bent by more than 0.5 mrad Planar channeling: even weaker, but significact planar deflection effect is seen (111) Si crystal, Bending angle is 3.1 mrad (to the left of the plots), hence R curv = 6 m (i.e. cannot expect 3.1 mrad bending)

16. 1996-1997: Germanium crystal (110) Ge crystal:50x10x1 mm 3 bent over 30 mm of its length Beam divergence: 450 GeV/c microbeam: 3  rad 200 GeV/c sec beam:  mrad (approx. 60% p, 40%  + )

19. 450 GeV/c protons 200 GeV/c hadrons Results for bending efficiency of Ge: up to 60% Good agreement with theoretical expectations

20. Radiation hardness A crystal has been irradiated in the T6 primary target for a full year with a 450 GeV/c slow-extracted proton beam of 5 10 12 ppp over 2.4 s every 14.4 s. The crystal was not aligned, the beam divergence was 0.2 mrad RMS. Total flux: 2.4 10 20 p/cm 2 over an area of 0.8 x 0.3 mm 2 Contact radiography: The bending efficiency was measured before and after the irradiation

21. The measurement was done with a classical 3-point bender. Deflection efficiency before irradiation: 50% Unfortunately the crystal broke into 2 pieces after the irradiation. Hence the distance between the two outer pins had to be reduced from 30 to 25 mm. This lead to a smaller radius of curvature and a correspondingly reduced channeling efficiency. Nevertheless the channeling and bending efficiency could be measured as a function of efficiency

22. Deflection efficiency measurement after irradiation 2.4 10 20 p/cm 2 C.Biino et al., CERN-SL-96-30-EA, published as EPAC 96:2385-2387

23. FOR NA48

24. Crystal serves to bend beam back over 7.2 mrad attenuate proton beam by large factor It replaces: a 5 m long dipole magnet a very small diameter pinhole It avoids muons to be bent back into the experiment

25. MECHANICAL DESIGN OF CRYSTAL HOLDER:

26. Reduce transmission by using coupling between H and V planes:

27. Transmission through the crystal : ≈ 2 10 -5

28. NA48 experience  Never had to replace a crystal  Never had to retune the crystal during a run  Very stable element in the beam  We consider it a very successful application  A crystal was also used as a photon converter to enhance photon conversion efficiency for a given thickness of the KS anti counter (C.Biino)

29. STUDIES WITH ION BEAMS Tests were performed with fully stripped Pb 82+ beams at 400- GeV/c (33 TeV) Theoretical expectations:   p = 7  rad, like for protons  Ions steered away from nuclei hence reduced nuclear interactiuons and reduced Weiszaecker-Williams break-up  Fraction channeled driven by beam divergence and dechanneling as for protons  Expect 16.8±2.5% deflection efficiency for a 4 mrad bend over 50 mm Si

30. First attempt (1996): Achieved 14±2%, consistent with theory

31. 1999 (H4 beam): 10 5 ions per SPS cycle 60x18x1.5 mm (110) Si crystal, bent over 55 mm with the 3-point bender also used in H8 Beam divergence 43  rad FWHM, measured by goniometer scan and double scan with two steering magnets (change only angle at crystal)

32. Hodoscope scans Dechanneling due to 3-point bender

33. 2001: Study of background and dechanneling (H4) 60x60 mm scintillator, operated at different HV but fixed threshold: sensitive to different charge states

34. Ions interact at rate much lower than in amorphous Silicon Indications that most of the lead comes out as Pb82+ But cannot exclude e.m. dissociation

35. Very recent results from 2003 Indium run (H2 beam): MUSIC – MUltiple Sampling Ionisation Chamber Si crystal, 60 mm long, bent over 56 mm Scan of S2. S3 coincidence

36. MUSIC output: Evidence of strong reduction (by factor ≈20) of nuclear charge changing interactions Direct beam Bent beam

37. Fig. 5. The fragmentation probability suppression η versus charge number in the upper region of Z for the bent beam for angles 7.5 mrad (filled squares: perfect alignment, open triangles: aligned at  p /2), 11.9 mrad (open circles) and 19.8 mrad (filled triangles).

38. A list of papers (1) Proton channeling

39. A list of papers (2) Ions NA48 Radiation Hardness LHC

40. Final remarks and conclusions  The H8 beam line is an excellent tool for crystal studies and qualification Its intrinsic divergence can be much smaller than the critical angle  p  Detailed studies of proton channeling could be done successfully in H8 with nice results and record deflection efficiencies for the full beam !  A crystal has been irradiated in the T6 target to a beam of 5 10 12 ppp with a 0.8x0.3 mm 2 FWHM spot size over a full SPS year. A 31% loss of deflection efficiency was observed for 2.4 10 20 p/cm 2  The H8 tests contributed to the development of a successful application of a bent crystal in the simultaneous K o beams for NA48. The crystal performed very well over many years and has been extremely stable. It never needed to be replaced.  Ion channeling has been studied in H4 (could have been done in H8). The channeling efficiency for Pb is similar as for protons, the outcoming particles are mostly of the same species as the incoming beam.