Nonintercepting electron beam size monitor using optical diffraction radiation interference

Abstract

In recent years, the use of diffraction radiation (DR), emitted when a charged particle beam passes\ud through a rectangular slit, has been proposed and successfully tested as a nonintercepting diagnostic of\ud high brightness beams. However, some problems related to the control of the particle trajectory through\ud the slit still remain. If an additional slit is placed in front of the first one, at a distance shorter than the\ud radiation formation length, interference between the forward diffraction radiation from the upstream slit\ud and the backward diffraction radiation from the downstream slit can be observed. In this paper we report\ud the first experimental observation of this effect, which we call here optical diffraction radiation\ud interference (ODRI). If the two slits have different dimensions and are not aligned on the same axis,\ud the properties of the ODRI pattern can be effectively used for nonintercepting beam diagnostics,\ud especially for the unambiguously determination of the beam size. Indeed, the advantage of ODRI\ud compared with a single aperture DR screen is due to the reduction of synchrotron radiation background,\ud the increase of sensitivity for transverse beam dimensions, and the possibility to separate effects caused by\ud the beam size and by beam offset within the slit

Non-intercepting diagnostic for high brightness electron beams using Optical Diffraction Radiation Interference (ODRI)

“…This setup is able to clearly estimate the emittance, the angular divergence and even the position of the beam inside the slit, as we already demonstrated in [7]. In this paper we further extend our study comparing the data obtained under the same beam condition but observing different wavelengths or polarization states.…”

“…An introduction and explanation of the ODRI theory can be found in [7]. Here we report just the fundamental details.…”

“…As clearly explained in [7] the two slits must be slightly misaligned with respect to each other (tens of microns), in order to allow the discrimination between the beam transverse size σ and the angular divergence σ'. The simultaneous measurement of both σ and σ' paves the way to use this device in order to directly retrieve the beam emittance.…”

Far- and near-field approximation for diffraction radiation

“…It should be underlined that after some angle the radiation will start to reflect again from the lower (or upper) half-plane of the second slit, but in our work we do not consider so big angles. In the paper [5] the research for the system with collinear slits was performed and it was shown that additional slit in the system can dramatically change DR angular distribution. In paper [6] changes in DR angular distribution, caused by shifting the slits were investigated.…”

“…For this reason the techniques based on Diffraction Radiation (DR) [1,2] were proposed and tested [3,4], adopting a single-slit geometry. In order to avoid some problems connected with this geometry, such as the impossibility to separate effects caused by both beam size and beam offset within the slit, a two slits system was proposed [5] and experimentally tested. Since in this system an additional slit is introduced, it becomes necessary to investigate effects caused by new parameters, which appear due to the second slit.…”