Optical Diffraction Radiation from a Beam Off a Circular Target

摘要

The use of optical diffraction radiation (ODR) as a diagnostic tool has increased in recent years. The potential of this technique has been demonstrated in several experiments at KEK (1), APS (2), FLASH (3) and possibly other facilities. These experiments were performed in extraction beam lines of lepton machines. However this technique can also be applied to high energy hadron beams. In this report we consider the ODR produced by such beams with the target as a round hole and apply the results to the Tevatron. This radiation is produced when a beam passes in the vicinity of a conducting target. The electro-magnetic fields due to the beam induce currents on the target and as the beam propagates, the currents change in time producing radiation both in the direction of beam propagation and along the direction of specular reflection from the target. This latter radiation, also termed backward diffraction radiation (BDR), is more useful for diagnostics since it can be directed out at the same longitudinal location as the target. This radiation is different from optical transition radiation (OTR) in which the beam passes through a metal target. Transition radiation is not suitable for continuous monitoring of a beam in a collider due to the beam energy loss and emittance growth and the fact that the target may be damaged. However the techniques for analyzing ODR are similar in many respects to those for OTR.