INFN Sezione di Ferrara, Dipartimento di Fisica e Scienze della Terra, Università di Ferrara Via Saragat 1, 44100 Ferrara, Italy.
Phys Rev Lett. 2013 Apr 26;110(17):175502. doi: 10.1103/PhysRevLett.110.175502. Epub 2013 Apr 24.
A graded Si(1-x)Ge(x) crystal has been manufactured for operation with high-energy protons to excite coherent interactions of the particles with the crystal such as channeling and volume reflection. The crystal had the shape of a parallelepiped though its (111) atomic planes were curved at a radius of 25.6 m because of the graded Ge content. The crystal was exposed to a 400 GeV/c proton beam at the external lines of CERN Super Proton Synchrotron to probe its capability to steer high-energy particles. Measured deflection efficiency was 62.0% under planar channeling and 96.0% under volume reflection. Such values are critically compared to their counterparts for a standard bent Si crystal under peer conditions. A Monte Carlo simulation of the dynamics of channeled and volume reflected particles in a graded crystal including the effect of Ge impurities and of lattice dislocations has been carried out. We found that the effect of crystal imperfections spoiled the efficiency of channeling while it negligibly affected the performance of volume reflection. We finally propose the usage of the graded crystal as a primary scatterer to aid halo collimation for the new generation of hadronic machines. As a unique feature, a properly cut graded crystal circumvents the problem of the miscut angle, which is currently a severe limitation for implementation of crystal-assisted collimation.
已经制造出了具有梯度 Si(1-x)Ge(x) 结构的晶体，用于高能质子激发，以实现粒子与晶体的相干相互作用，如沟道和体积反射。尽管其（111）原子面由于梯度 Ge 含量而弯曲成半径为 25.6 米的形状，但该晶体呈平行六面体形状。该晶体在 CERN 超级质子同步加速器的外部线路上暴露于 400 GeV/c 的质子束下，以探测其引导高能粒子的能力。在平面沟道下测量的偏转效率为 62.0%，在体积反射下为 96.0%。这些值与在同等条件下的标准弯曲 Si 晶体的对应值进行了严格比较。已经进行了包括 Ge 杂质和晶格位错影响的梯度晶体中沟道和体积反射粒子动力学的蒙特卡罗模拟。我们发现，晶体缺陷的影响破坏了沟道的效率，而对体积反射的性能影响可以忽略不计。最后，我们提出将梯度晶体用作初级散射体，以帮助下一代强子机器的晕圈准直。作为一个独特的特点，适当切割的梯度晶体规避了目前在实现晶体辅助准直方面存在的晶面切割角问题。
