Abstract
The channeling process in bent silicon crystals are used since '70s to manipulate beams of high energy particles. During the last decade, several studies and experiments carried out by the UA9 Collaboration at CERN demonstrated the possibility to use bent crystals for beam collimation, extraction, focusing and splitting in particle accelerators. These crystals are subject to deterioration due to the interaction of the particles with the crystal lattice, degrading the beam steering performance. For this reason, robustness tests are crucial to estimate their reliability and operational lifetime. A ∼8% of reduction in channeling efficiency on crystals irradiated with 2.5·1021/cm2 thermal neutrons was measured and reported in this manuscript. Extrapolations to possible operational scenarios in high energy accelerators are also discussed.
Highlights
: The channeling process in bent silicon crystals are used since ’70s to manipulate beams of high energy particles
The UA9 experimental apparatus used in H8 to measure crystal angle and channeling efficiency is based on a high angular resolution telescope, able to reconstruct incoming and outgoing particle single tracks with respect to the crystal position on a lever arm of 10 m
Further tests to evaluate the robustness of silicon crystals in case of accidental fast irradiation during machine operations have been performed by UA9 at the CERN HiRadMat facility [25,26,27]
Summary
These measurements have been performed at the H8 SPS extraction line using 180 GeV/c secondary hadron beam (∼ 70% protons and ∼ 30% positive pions) and with the following parameters: σx 1.6 mm, σy 2 mm, σθx 31 μrad, σθy 44 μrad. The nine crystal samples are all identical in terms of material and dimensions, only the bending angle is slightly different to cover the bending angle range used in accelerator operations Their characteristics are reported in table 1 and have been chosen to be as similar as possible to those of crystals used for LHC and SPS applications [2,3,4] and following the irradiation capsule constraints at the same time. The critical bending radius Rc, above which particles can no longer be trapped between crystalline planes, is ∼ 31.6 cm for 180 GeV positive particles channeled along (110) planes in silicon crystals [1] For both the measurements, before and after the irradiation, the bending radius of the crystals varies between 15.5 m and 46.5 m. All the measurements have been performed in the same experimental conditions and following the same procedures
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