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Motivated to create a technology that could monitor, in real time, the full volumetric beam properties of an incident x-ray beam, a group of researchers from SUNY Stony Brook, Brookhaven National Laboratory and Case Western Reserve University have invented, fabricated and tested a new pixelated diamond x-ray beam “window” detector that could promise to revolutionize beamline design. A report describing the fabrication and tests of this new detector, the most recent of which utilized the G3 station at CHESS, is highlighted as the cover art in the current issue of Journal of Synchrotron Radiation (see figure) [1]. The work builds on the group’s pioneering success in developing single- and quad-region detectors that operate in a similar manner, now available commercially through Sydor Instruments (http://sydortechnologies.com/imaging-detectors/x-ray-beam-monitors). In each case, the devices are based on sufficiently high quality, synthetic single-crystal diamonds — only available within the last decade or so — that they can function as x-ray transparent diodes: thin electric contacts on the front and back of the diamonds are used to place a voltage across the device, and allow photocurrent generated in the diamond by the incident x-ray beam to be extracted and measured. In effect, the single-pad version of these devices acts similarly to an ion chamber. In stark contrast to ion chambers, however, these devices can operate in vacuum or atmospheric pressure, are only few mm thick, and have far greater dynamic range — up to 11 orders of magnitude. Their dynamic range makes them perhaps the only means of obtaining direct, in-line, quantitative monitoring of high flux white-beam synchrotron-based beamlines.

JSR cover 151101

Cover of the recent JSR edition showing (top) a schematic of the new pixelated diamond transmission mode x-ray beam diagnostics detector and (bottom) a detected x-ray beam shape footprint for different focus levels of a toroidal mirror.

What’s new here is the extension of the work described above to a full, 2D imaging detector by means of dividing the front and back contacts of the device into 32 independently addressable stripes. The front- and back-contact stripes are rotated by 90 degrees with respect to one another, allowing the photocurrent from each of 1024 pixels to be separately measured. Two detectors were demonstrated, with pixel pitches of 60 and 100 microns, and read-out speed of up to 30 Hz.

The performance of the X-ray detectors was evaluated at beamline X28C at the NSLS and at beamline G3 of the Cornell High Energy Synchrotron Source (CHESS). The NSLS measurements utilized a toroidal-focused white beam on a bend-magnet line. The experiments at the CHESS G3 station utilized monochromatic 11.2 keV beam from an undulator source. Motivation for the new detector was to provide data necessary to characterize, adjust and optimize the focusing of x-ray beams by mirrors. (Coincidentally, on a recent visit to CHESS made after the report, the detector proved itself quite useful to help commission a new focusing mirror on the G3 station.) Test results show the novel detectors provide precise beam position (noise ~1%) and morphology information (shape to within 2%) and flux measurements to 1%.

Looking forward, this new technology can serve x-ray beamlines in a multitude of ways including total flux monitors, x-ray beam position monitors, and x-ray footprint shape diagnositics, any or all of which can help diagnose and optimize the performance and stability of x-ray storage rings and x-ray beamline optical components. The group mentions continuing developments to incorporate these devices into vacuum-vacuum or vacuum-air windows.

Reference:

[1] Zhou, T., Ding, W., Gaowei, M., De Geronimo, G., Bohon, J., Smedley, J. & Muller, E., “Pixelated transmission-mode diamond X-ray detector,” J. Synchrotron Rad. 22, 1396-1402 (2015).

 

 

Submitted by: Ernest Fontes and Arthur Woll, CHESS, Cornell University
11/15/2015