Specification for diamond crystal radiator

Rocking curve width	15 μr r.m.s. maximum
Thickness	20 μm maximum
Size	5 mm x 5 mm minimum
Plate shape	rectangular or square
Orientation	<001>
Orientation error	2° maximum
Variation in thickness	±2μm maximum

 

The quality requirements for the Gluex diamond radiator are mainly driven by the requirement for the polarization of the photons by the GlueX project. The two things which affect the photon polarization are the mosaic spread and crystal thickness. In order to get the necessary photon polarization, the mosaic spread must be less than 15 micro radians (r.m.s.) for the whole crystal and the thickness must be less than 20 microns. The mosaic spread can be estimated from the rocking curve width. The size of the diamond crystal is determined by the electron beam spot size, since the electron beam has an size of 1.7 mm r.m.s. by 0.5 mm r.m.s. , the size of the crystal must be larger than 5 mm by 5 mm. Detailed calculations for these requirements can be found in the GlueX concept design report (CDR) chapter 4.

Variation of the thickness over the whole crystal should be less than ±2 microns. The crystal plate should have either rectangular or square shape. The orientation of the crystal should be <001>, the error of the orientation should be less than 2 degrees. The crystal plate should be free from cracks.