Private:Production of Coherent Bremsstrahlung Radiators from CVD Diamond

This paper aims to describe characterization of diamond radiators under development by the UConn PAN group for the GlueX experiment in Hall D at Jefferson Lab.

The following outlines the content of the paper by section with topics, figures, tables, references etc.

Title
The title of this page is a working title for the paper. Suggestions are sought for a more precise title

Author List
The following is a tentative author list. At the moment, the scope of the paper is not known and therefore the list of contributors is not set. Further, the protocol for the author list precedence is not known in general and for the targeted journal so the ordering has not been thoughtfully reviewed.


 * I. Senderovich
 * B. Pratt
 * J. McIntyre
 * C. Pelletier
 * K. Finkelstein
 * R.T. Jones

Characterization Technique/Methods
The beam line C at the Cornell High Energy Synchrotron Source allows placement of samples 14.5m from the bending magnet. To minimize the angular dispersion, increase the beam size and pick out the 15keV component, a double bounce silicon monochromator is assembled upstream of the experimental hutch using the (3,3,1) planes. Samples are mounted on a thin stretched mylar membrane that is attached to a four-axis goniometer with arc-second resolution in the Bragg angle.

In order to verify the configuration of the silicon monochromator and other aspects of the setup, another silicon crystal wafer was used as a sample. It was oriented to study the (3,1,1) planes to check the matching with the monochromator. Being a sample of well known crystal lattice orientation across its surface, this procedure offered a check on the distortions introduced by the sample holder. This procedure demonstrated that instrumental resolution in the rocking curve of less than 10&mu;r was achieved but that the variation of the rocking curve centroid along the wafer surface is many times this quantity due to the warping by the stretched mylar mount.

Full crystal rocking curves of all the samples were then examined in two orthogonal orientations in order to build a map of local (2,2,0) plane normal vectors. The root mean square distribution of their orientations represents the principle figure of merit for a diamond radiator sample.

Results








Figures 1 and 2 show the rocking curve width and centroid (respectively) as a function of position on the non-electron grade "plate" surface. Figures 3 and 4 represent the same for a thinned "plate". Comparing these sets, it is evident that apart from "hot spots" where significant structural damage must have occurred during thinning, the local crystal structure maintains small mosaic spread after thinning. However, the centroid of the rocking curves, equivalent to the local normal to the scattering planes, is broadly distributed in the thin sample. The virgin thick plate appears to maintain the crystal orientation rigidly, whereas the thinned diamond loses its tensile strength and develops internal strains that result in a curved natural shape. It is this contribution that is the primary challenge in developing a thin diamond radiator with narrow whole crystal (averaged) rocking curve.