A single crystal CVD diamond x-ray beam diagnostic with embedded graphitic wire electrodes

A single crystal CVD diamond detector with graphitic wire electrodes running beneath the diamond surface has been fabricated. This detector design is novel in that there is no surface metallisation present within the active region, and so the detector is a uniquely transmissive X-ray beam diagnostic instrument. This detector is designed to simultaneously measure the position, profile, and flux of an incident beam. It has applications in beam position and profile monitoring, and active beam feedback and stabilisation. To achieve this, a short-pulse laser, focused to micron-sizes using adaptive optics, can be used to graphitise arbitrary wire paths within bulk diamond. Presented in this paper is a transmissive X-ray pixel detector design with a 50-micrometre pixel pitch created using this technique. This pixel detector is produced by fabricating two separate arrays of parallel wires running under the surface of a diamond plate. The two arrays run perpendicular to each other, and parallel to the diamond surface. They are separated within the material by a depth of 100 microns. The parallel wires within each array are separated by 50-microns, and this is what determines the pixel pitch. Each of the crossing points between two wires from each array acts as a pixel. The signal from each pixel may be read out by measuring the signal current from each wire in one array whilst applying a bias voltage alternately to each wire in the other, perpendicular array. Alternatively, it is proposed to modulate the bias applied to each wire at a different frequency, from which the 2-dimensional beam profile may also be measured using a lock-in technique. This paper will provide an overview of the fabrication techniques for this first prototype detector, and provide a discussion of signal readout methods that will be used. An outline of the planned experimental tests is given.