Crystal collimation for LHC

1. Crystal collimation for LHC Valery Biryukov IHEP Protvino Vincenzo Guidi Ferrara University and INFN Walter Scandale CERN CERN, Geneva, 24 April 2003

2. Borrowed from Ray Fliller’s talk at Paris EPAC 2002

3. Crystal Channeling

4. Beam line (70 m long) made of 3 crystals, IHEP

5. Beam focusing by crystal

11. Crystal design as used at IHEP Protvino and RHICCrystal is 3 to 5 mm along the beam

13. Crystal SQUEEZE Beam Direction 5mm Crystal Courtesy of IHEP, Protvino

14. New crystal design (“strip”) gave 85% efficiency at IHEP

16. Typical beam phase space at crystal location, IHEP

17. 1- circulating beam, 2- extracted beam, IHEP

18. Crystal extraction efficiency as measured since Dec 1997.85% is measured even when all stored beam is dumped onto crystal

20. Deflected (left) and incident (right) beamsas seen downstream of the crystal • Prior to the test, the crystal was exposed in the ring to 50-ms pulses of very intense beam (about 1014 proton hits per pulse). • No damage of crystal was seen in the test, after this extreme exposure.

21. Beam profile at collimator face with NO crystal, 70 GeV

22. Misaligned x

23. Crystal collimation

24. Effy vs Energy

25. 45 GeV

26. 12 GeV

27. Crystal lifetime is order of 5*1020 proton/cm2

28. RHIC Crystal Collimator Setup 8 Upstream PIN diodes 4 Downstream PIN diodes Data fill focus on upstream PIN diodes

29. Layout of RHIC experiment on crystal collimation

31. RHIC measurements, EPAC 2002

32. Simulations of LHC crystal collimation

33. Simulations with smaller bending, 0.1 mrad

34. Two bending options compared: 0.2 and 0.1 mrad

35. Efficiency vs bending angle

36. Background suppression factor vs crystal bending

37. FNAL simulations for Tevatron crystal scraping, PAC 1999

38. Conclusion • Simulations and experiments promise • 10-fold improvement in backgrounds • at TeV accelerators if bent crystal is used as primary scraper. • No problems with high intensity or lifetime.

39. Extraction parameters • Protons • Energy at 1.3-70 GeV • Intensity 1012 protons in spills of 2 s duration • Efficiency greater than 85% • Equivalent to 1000 T dipole magnetic field Extraction efficiency vs. crystal length at 70 GeV

40. Structure of the bending crystal • Dimensions 0.5250mm3 • 1/R is the curvature experienced by channelled protons

41. Bending device • Bending exploits anticlastic effects due to anysotropy of crystalline Si • For the (111) direction the sample takes the shape of a saddle

42. Preparation of the Si samples I • Starting material is prime-grade, (111) oriented 525-m-thick silicon wafer • In previous runs there came out that a surface layer as thick as 30 m was rich in scratches, dislocations, line defects and anomalies that would reduce channelling efficiency • Such a layer originated in the mechanical cutting for manufacturing the samples • Thus we attempted removal of the layer

43. Preparation of the Si samples II • Preliminary cleaning to organic and metallic impurities from the surface of the wafers by H2O2, NH4OH, HF, HCl,... • Coverage of the largest surfaces by Apiezon wax • Cutting of the samples by a diamond-blade saw avoiding alignment with major crystalline axes. • Planar etching (HF, HNO3 and CH3COOH, 2:15:5) with a timing set for 30 m thinning. More info in Rev. Sci. Instrum. 73 (2002) 3170-3173

44. CRYSTAL S3 S4 EM S1 S2 VACUUM PIPE 7 meter Images of the beam deflected through mechanically treated (left) and chemically polished crystals (right)