In-Air X-Ray Detectors

General description :

Crotch or beamport absorbers deal with the unused power of the synchrotron radiation generated by dipoles in electron storage rings.  However, a tiny fraction of the very hard X-Rays fully penetrate the ESRF Storage Ring absorber structure, which presents 40mm of Copper + 5mm of Steel, and enter the free air space behind it. 

At the ESRF it was first shown in 2005 that this tiny leakage power can be detected by a simple, compact and low-cost device consisting of a scintillator with optics & camera. Situated In-Air just behind the absorber it precisely measures the vertical electron beamsize.

A more sensitive imaging detector, still operating in-Air and with an ordinary non-cooled CCD device, was also applied for 1us, 5mA single shot measurements in the ESRF transferline, where the X-Rays traverse the vacuum chamber wall, in a path of 10mm of Steel.

In 2006, such a simple In-Air  imaging detector was also installed at the ANKA light source in Karlsruhe, Germany. ANKA’s electron beam is of medium energy but its relatively thin (8mm Copper) absorber allows for enough signal. Its installation & alignment was quick and straight-forward.  It measures the vertical beam dimensions with high resolution and precision.

A second detector type has been developed at the ESRF; Using the same leakage X-Rays, it consists of a high-Z blade in combination with a small In-Air ionization volume. It generates a direct electric signal that is used for nanometer resolution measurements of vertical beam motion in a spectrum up to 1KHz.

Presently (2007) we are in the process of installing five detectors of the imaging type, and 12 detectors of the ‘electric’ type with blade & ionization volume.

References & links of relevant papers and presentations :

B.K.Scheidt, "In-Air X-Ray Detectors : A New Field of Simple and Powerful Beam Diagnostics" (pdf file)

B.K.Scheidt, “Detection of Hard X-Rays in Air for Precise Monitoring of Vertical Position & Emittance in the ESRF Dipoles”, DIPAC’05, Lyon, 6-8June 2005.
http://accelconf.web.cern.ch/AccelConf/d05/PAPERS/CTWM01.PDF

A-S.Müller, et al., “Precise Measurements of the Vertical Beam Size in the ANKA Storage Ring with an In-air X-ray ”, EPAC’06, Edinburgh, 26-30June 2006.
http://accelconf.web.cern.ch/AccelConf/e06/PAPERS/TUPCH032.PDF