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

Borrowed from Ray Fliller’s talk at Paris EPAC 2002

Crystal Channeling

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

Beam focusing by crystal

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

Crystal 5mm Beam Direction Crystal Courtesy of IHEP, Protvino

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

Typical beam phase space at crystal location, IHEP

1- circulating beam, 2- extracted beam, IHEP

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

Deflected (left) and incident (right) beams as 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 proton hits per pulse). No damage of crystal was seen in the test, after this extreme exposure.

Beam profile at collimator face with NO crystal, 70 GeV

Misaligned x

Crystal collimation

Effy vs Energy

45 GeV

12 GeV

Crystal lifetime is order of 5*10 20 proton/cm 2

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

Layout of RHIC experiment on crystal collimation

RHIC measurements, EPAC 2002

Simulations of LHC crystal collimation

Simulations with smaller bending, 0.1 mrad

Two bending options compared: 0.2 and 0.1 mrad

Efficiency vs bending angle

Background suppression factor vs crystal bending

FNAL simulations for Tevatron crystal scraping, PAC 1999

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.

Extraction parameters Protons Energy at GeV Intensity 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

Structure of the bending crystal Dimensions 0.5  2  50mm 3 1/R  is the curvature experienced by channelled protons

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

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

Preparation of the Si samples II Preliminary cleaning to organic and metallic impurities from the surface of the wafers by H 2 O 2, NH 4 OH, 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, HNO 3 and CH 3 COOH, 2:15:5) with a timing set for 30  m thinning. More info in Rev. Sci. Instrum. 73 (2002)

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