The electromagnetic radiation of a charge moving in an infinite 3D structure made of parallel wires is considered. The periods of the structure are assumed to be small; therefore, it can be described by an effective permittivity tensor. The charge velocity is perpendicular to the wires. Analytical and numerical investigations are performed, and some unusual properties of the radiation are noted. It is shown that the radiation propagates along the wires and concentrates near certain rays behind the charge. The wave field does not vary with distance from the charge along these rays (if energy loss in the medium is negligible). The prospects for the use of the structure under consideration for diagnostics of bunches are noted.
We proceed with investigation of specific dielectric target that effectively concentrates Cherenkov radiation from a charged particle bunch into a small vicinity of the focus point located at the symmetry axis of the target. The case of "non-ideal concentration" where the charge velocity differs from the designed one was considered theoretically in our previous paper. In particular, we have noted that geometrical rays form caustics in this case, and areas of radiation concentration are shifted with respect to the designed focus point. Since the direction of this shift relates to the sign of the charge velocity deviation, this effect can be used for diagnostics of bunch velocity. Here we perform numerical simulations in COMSOL using frequency domain solver and compare simulated results with theoretical ones. In particular, we show that simulated focus area is indeed shifted with change in charge velocity and the position of this area correlate very well with analytical predictions.
A theoretical investigation of radiation field produced by a charge moving through the dielectric concentrator for Cherenkov radiation is performed for the general case where a charge trajectory is shifted with respect to the target axis. The idea of dielectric target with specific profile of the outer surface was presented and investigated in our previous papers for the symmetric case. Here we show how non-symmetric field components generated in the bulk of target affect field distribution near the focus where strong concentration of the energy occurs. Possible applications of this target are discussed. arXiv:1904.05188v3 [physics.acc-ph]
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