High resolution X‐ray diffraction study of single crystal diamond radiators

Abstract

High quality single crystal diamond is widely used for generating highly polarized high energy photon beams in the photonuclear physics study. The quality of the diamond crystal has a vital effect on the polarization of the photon beam which should be as high as possible as required by the experiments at Jefferson Lab, MAX_lab and MAMI, etc. One 20 µm thick diamond radiator from Jefferson lab and one 100 µm thick diamond radiator from MAMI were investigated by X‐ray rocking curve and topograph measurements. The rocking curve results suggest that the 20 µm thick diamond radiator is severely deformed which explains why this diamond radiator showed unstable performance in the coherent bremsstrahlung experiments. The 100 µm thick diamond radiator was radiation damaged after being used in an 855 MeV electron beam line for several years. At the radiation damage region, it was found that the rocking curve width is significantly broadened, and the rocking curve peak position shifted towards the larger angle side by around 200 arcsec. Raman test confirmed that a significant amount non‐diamond phase exist at the radiation damage region.

The GlueX beamline and detector

“…HPHT crystals had been thought to be far superior to CVD single crystals in terms of their di↵raction widths, but our experience did not bear this out. GlueX measurements of the x-ray rocking curves of CVD crystals obtained from the commercial vendor Element Six 24 routinely showed widths that were within a factor 2 of the theoretical Darwin width, similar to the results we found for the best HPHT diamonds that were available to us [11,12]. Fig.…”

“…This new facility starts with an extracted electron beam at the north end of the Continuous Electron Beam Accelerator Facility (CEBAF) [5,6]. The electron beam is delivered to the Tagger Hall, where the maximum energy is 12 GeV, due to one more pass through the north linac than the other experimental halls (A, B and C). Here, linearly-polarized photons are produced through coherent bremsstrahlung o↵ a 50 µm thick diamond crystal radiator.…”

“…Pulses are identified by the first sample that exceeds a threshold, currently set to 5 (8) counts above the average pedestal for the BCAL (FCAL). These thresholds correspond to approximately 2.5 (12) MeV. The integral is determined using a fixed number of samples relative to the threshold crossing, which was determined by maximizing the ratio of signal to pedestal noise.…”

The GlueX Beamline and Detector

“…HPHT crystals had been thought to be far superior to CVD single crystals in terms of their diffraction widths, but our experience did not bear this out. GlueX measurements of the x-ray rocking curves of CVD crystals obtained from the commercial vendor Element Six 23 routinely showed widths that were within a factor 2 of the theoretical Darwin width, similar to the results we found for the best HPHT diamonds that were available to us [11,12]. Fig.…”

“…This new facility starts with an extracted electron beam at the north end of the Continuous Electron Beam Accelerator Facility (CEBAF) [5,6]. The electron beam is delivered to the Tagger Hall, where the maximum energy is 12 GeV, due to one more pass through the north linac than the other experimental halls (A, B and C). Here, linearly-polarized photons are produced through coherent bremsstrahlung off a 50 µm thick diamond crystal radiator.…”