Specification for diamond crystal radiator

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Rocking curve width20 μr r.m.s. maximum (integrated over the whole crystal active area)
Thickness20 μm in the active area
Size 5 mm x 5 mm minimum active area
Plate shape rectangular or square
Orientation <001>
Orientation error5° maximum
Variation in thickness ±5μm 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 (integrated over the whole crystal) must be less than 15 micro radians (r.m.s.) 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 ±5 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 5 degrees. The crystal plate should be free from cracks.