Diffraction Radiation Beam Size Monitor

Diffraction radiation (DR) is produced when a relativistic charged particle moves in the vicinity of a medium. The electric field of the charged particle polarises the target atoms which then oscillate, emitting radiation with a very broad spectrum. The spatial-spectral properties of DR are sensitive to a range of electron beam parameters. Furthermore, the energy loss due to DR is so small that the electron beam parameters are unchanged. DR can therefore be used to develop non-invasive diagnostic tools. To achieve the micron-scale resolution required to measure the transverse (vertical) beam size using incoherent DR in CLIC, DR in UV and X-ray spectral-range must be investigated. Experimental validation of such a scheme is ongoing at CesrTA. The "medium" in the CesrTA experiment, is a thin silicon wafer. The beam is made to pass through a slit in the wafer so that diffraction radiation is generated by both edges. The slit with a width of about 0.5 mm, is etched in the silicon. One of the challenging aspects of the experiment is to steer the beam through the very small aperture. A special vacuum chamber with motorized arm for inserting the fork into the beam was built at CERN and installed in CesrTA. The chamber is instrumented with a camera to observe the diffraction radiation.