Absolut mätning av Cherenkov-diffraktionsstrålning i det synliga området

In this report, we present our contribution to the ongoing investigation of the radiation emitted by a relativistic charged particle traveling in the vicinity of a dielectric medium, known as Cherenkov Diffraction Radiation (ChDR). Previous studies have identified ChDR as a promising candidate for non-invasive beam diagnostics in future accelerators, primarily due to its large emission angle and high directivity. However, the feasibility of employing ChDR-based diagnostic instruments remains uncertain, largely because of significant discrepancies between theoretical predictions of the radiated spectrum. Although in previous years, ChDR has been experimentally observed in a variety of settings, these efforts have not focused on measuring the absolute radiation yield. The first attempt to measure the absolute radiation yield was carried out in 2023 at the Accelerator Test Facility (ATF2) at KEK, Japan. The beam in this facility, has a high Lorentz factor and a transverse size on the order of micrometers. As a result, when the radiator is brought sufficiently close to the beam, Cherenkov Diffraction Radiation (ChDR) is emitted in the visible range.However, the measurements revealed that the signal at such close distances is heavily contaminated, with beam halo particles identified as the likely source of this signal pollution. Indeed, when a halo particle enters the radiator, it emits conventional Cherenkov radiation at intensities several orders of magnitude greater than that of ChDR, drowning the desired signal. The first part of the work presented in this report focuses on improving the data processing pipeline and characterizing the experimental setup. A detailed understanding of the response of each component in the setup is essential for achieving an absolute measurement of the radiation yield. The photon-counting detection system consisted of optical filters, polarizers, a lens, an image intensifier, and a CMOS sensor. The transmission spectra of the optical filters and polarizers were measured, as was the efficiency of the intensifier unit in combination with the lens and CMOS sensor. Additionally, the photon-counting process was refined through the use of neutral-density filters during data acquisition and the implementation of a segmentation-based detection algorithm. The second part of this work presents the design of a collimator system capable of shielding the radiator from halo particles without generating problematic secondary radiation. This study was grounded in the theoretical understanding of electron–matter interactions in the GeV energy range and supported by Monte Carlo simulations. The shielding effectiveness was evaluated numerically for materials of varying density and subsequently tested experimentally using a ten centimeter tungsten block at ATF2.