Steering of a Sub-GeV Electron Beam through Planar Channeling Enhanced by Rechanneling

Abstract

We report the observation of efficient steering of a 855 MeV electron beam at MAMI (MAinzer MIkrotron) facilities by means of planar channeling and volume reflection in a bent silicon crystal. A 30.5 μm thick plate of (211) oriented Si was bent to cause quasimosaic deformation of the (111) crystallographic planes, which were used for coherent interaction with the electron beam. The experimental results are analogous to those recorded some years ago at energy higher than 100 GeV, which is the only comparable study to date. Monte Carlo simulations demonstrated that rechanneling plays a considerable role in a particle's dynamics and hinders the spoiling of channeled particles. These results allow a better understanding of the dynamics of electrons subject to coherent interactions in a bent silicon crystal in the sub-GeV energy range, which is relevant for realization of innovative x-ray sources based on channeling in periodically bent crystals.

Planar channelling of relativistic electrons in half-wave silicon crystal and corresponding radiation

“…The standard deviation of the distribution matches the experimental value of 0.1 mrad. Thus, two thousand mrad which is comparable to that for planar channeling in bent crystals [6,7] because the critical angle increases at lower energies. The fraction of deflected particles calculated by Gaussian gives 29% [14].…”

“…These early studies have been carried out using positively charged particles. Recently, these techniques has been proven to be useful even for negatively charged particles -relativistic electrons -at MAMI (855 MeV [6]) and at SLAC (3.35 and 6.3 GeV [7]). These experiments showed that there appear a large deflection angle in the channeling orientation and a smaller one in the volume-reflection orientation.…”

Backscattering/transmission of 2MeV He++ ions quantitative correlation study

“…Under the planar channeling condition [1,2], during transmission of energetic particles through crystal planes in the harmonic (oscillator potential) approximation, effect of coherence can be established under circumstances of phase summation, which depend on the periodical arrangement of the crystal atoms at selected beam parameters. Planar oscillations are induced by the interacting potential U pl (p), which is experienced by the energetic particle as a sum of the potentials generated by the strong electromagnetic field between crystal planes where the channeled oscillations occur.…”

Experimental evidence of independence of nuclear de-channeling length on the particle charge sign

“…For negatively charged particles, since the minimum of the potential well is located on the atomic planes, the mechanism of electronic de-channeling has a negligible contribution ( f e ∼ 0, f n ∼ 1) because all the particles do interact with nuclei [5,6,26]. Therefore, the channeled-particle fraction f ch,− holds,…”

“…Measurements proved the capability of channeling for manipulation of positively [4] and negatively [5,6] charged particle beams from MeV [7] up to hundreds of GeV [8,9], and for the generation of intense electromagnetic radiation from sub-GeV [10,11] to hundreds-GeV electron beams [12]. Moreover, channeling effects were exploited for steering [13], collimation [14] and extraction [15] of relativistic beams in circular accelerators, as well as splitting and focusing of extracted beams [16], a e-mail: bagli@fe.infn.it leading to the installation of two bent crystals in the Large Hadron Collider (LHC) for collimation purposes [17].…”