Goals and purpose
Halo particles in circular accelerator represent a threat for the good performance, stability and protection of the machine. Specific beam collimation system must be designed and implemented based on passive objects able to scatter and absorb undesired particles. In the last years bent crystals have been efficiently used to extract beam particles out of an accelerator using the coherent interaction of the charged particles with the crystal (crystal channeling). The crystal extraction can be therefore applied to the main beam but also to halo particles. A crystal assisted collimation system for hadron colliders (as the Large Hadron Collider, LHC) has been proposed. A classic two-stage collimation system in accelerators consists of a primary element acting as a small scattering target and a secondary element absorbing particles impinging on it. An amorphous primary target scatters particles in no preferred direction while a bent crystals traps particles with the coherent scattering on aligned atomic planes and kicks them in only one direction. The halo protons can be redirected so that they hit the secondary absorber with a large impact parameter and, therefore, can be efficiently removed. CERN approved in 2008 the UA9 experiment with the aim of testing directly the crystal assisted collimation as an alternative for both protons and lead ion beam collimation in the LHC.
UA9’s final goal is to demonstrate that a crystal based collimation has a higher cleaning efficiency than traditional scheme.
The UA9 experimental layout (arXiv:1106.5861v1 [physics.acc-ph] 29 Jun 2011)