New X-ray scattering-based beam position monitor for high power synchrotron radiation

Abstract

A new method of beam position monitoring for white synchrotron X-ray radiation has been developed. This method utilizes X-rays scattered from a graphite filter originally placed in the beam’s path to absorb the low-energy portion of the white beam. The graphite filter acts as an optical source plane for scattered X-rays at the beam’s footprint. The scattered X-rays exit the vacuum chamber and an image of the beam footprint is created using a pin-hole camera arrangement in combination with a phosphor screen and a CCD camera. The CCD camera records the image frames of the X-ray footprint from which a centroid position of the intensity is calculated. With proper calibration, the centroid position is easily converted to a beam position in microns. We have found that the intrinsic precision for determining the centroid position of an LED image of the camera system on an optical bench is about 0.06 microns.The new beam position monitor has been tested during a dedicated machine study when the X-ray beam position was changed by small amounts using local positron beam position controls. . The measurement error (standard deviation) of the actual X-ray beam position measurement was about 0.6 microns. In addition to providing beam position information the new device also provides vertical beam intensity profile and total beam intensity.