Channeling and radiation experiments at SLAC

Abstract

Since 2014, a SLAC-Aarhus-Ferrara-CalPoly collaboration augmented by members of ANL and MIT has performed electron and positron channeling experiments using bent silicon crystals at the SLAC End Station A Test Beam as well as the FACET accelerator test facility. These experiments have revealed a remarkable channeling efficiency of about 24% under our conditions. Volume reflection is even more efficient with almost the whole beam taking part in the reflection process. A positron experiment demonstrated quasi-channeling oscillations for the first time at high beam energy. In our most recent experiment we measured the spectrum of gamma radiation for crystal orientations covering channeling and volume reflection. This series of experiments supports the development of more advanced crystalline devices capable e.g. of producing narrow-band gamma rays with electron beams or studying the interaction of the electrons with the wakefields generated in the crystal at high beam intensity.

First design of a crystal-based extraction of 6 GeV electrons for the DESY II Booster Synchrotron

“…The maximal deflection efficiency is slightly above 1 %. Though this number is considerably lower of the efficiency registrated previously in the experiments [20][21][22][23][24][25][26][27], it doesn't represents itself as an efficiency of extraction. Indeed, not only channeling particles may reach the septum magnet entrance, but also the dechanneled ones.…”

“…This will make high quality intense electron beams more accessible for a larger community, and consequently, will considerably speed up nuclear and particle physics detectors and generic detector R&D, as well as will be very useful for many projects in high-energy physics requiring fixed-target experiments. Some applications of crystals as X-ray and gamma source [26,27,[30][31][32][33][34][35][36][37][38][39][40][41] and a positron source [65,66] could be also tested in these experiments. Furthermore, since FCC-ee is becoming the main after-LHC collider project, electron/positron crystal-based extraction may provide an access to unique experimental conditions for ultra-high energy fixed-target experiments to measure e.g.…”

“…However, recent experiments at both the Mainz Microtron MAMI (855 MeV electrons) [20][21][22] and the SLAC FACET facility (multi-GeV electrons) [23][24][25][26][27] with the new generation of bent crystals developed by INFN Ferrara group [22,28,29] demonstrated channeling efficiencies in the range from 10 to 40 %, i.e. of the same order of magnitude as for protons.…”

“…These crystals were developed not only as beam steering devices, but also as innovative X-and γ-ray radiation sources [26,27,[30][31][32][33][34][35][36][37][38][39][40][41] based on the effect of channeling radiation (CR) [42,43]. This type of radiation allows to considerably increase the radiation intensity in comparison with bremsstrahlung.…”