Non-intercepting electron beam diagnostics using diffraction ra- diation

The Linear Collider presents new challenges for beam instrumentation. Some of the beam dimensions are of the order of a few nm (at the i.p.), and to be able to reach these small sizes, the beams have to be tightly controlled and understood from their very inception onward. A number of different techniques are available in the arsenal of beam size and beam emittance measurements (e.g. transition radiation, metal wire, laser wire, laser interferometry, cavity BPM). Experiments of electron bunch profile measurements have been conducted using coherent synchrotron radiation (CSR), coherent transition radiation (CTR), as well as coherent diffraction radiation (CDR) [1, 2, 3, 7]. Because the CDR perturbs the electron beam less than CTR, it is a better choice for monitoring the electron beam bunch shape. The use of diffraction radiation (DR) for measuring the transverse beam dimension is a new non-invasive technique, only partially investigated at the present time [4, 5]; for example transverse beam size and emittance measurements have not been performed even though it is apparently possible to make precision measurements of bunch length, emittance at low energies, and the transverse size. (A recent experiment at KEK, by a Japan-Russia collaboration, has presented vertical beam size measurements using optical diffraction radiation[9].