Optical transition radiation diagnostics for ion beams

Transition radiation (TR) refers to the emission of electromagnetic radiation when a charged particle moves across an optically inhomogeneous region like the interface between two media with different dielectric properties. Transition radiation have applications in detection of high-energy particles, coherent radiation sources, beam diagnosis etc. With advances in material science and nanotechnol_24ogy, there are some recent studies on shaping the properties of Transition Radiation by artificially engineered materials.

Charge distribution diagnostics, typically called beam profiling in transverse plane and beam charge or current monitoring in longitudinal plane, are fundamental diagnostic requirements for accelerator operation and optimization. There are several established methods like secondary electron monitor (SEM) grids as well as beam induced fluorescence (BIF) for transverse beam profile measurement, however, with rapid advances in accelerators and beam dynamics, the suitability of these methods is under question for fast radiation-hard diagnostics in context of heavy ion beams.

They are limited by resolution of the measured profiles, fundamental limits on signal generation processes and the effect of measurement apparatus on beam profile.

Optical transition radiation (OTR, i.e. TR in visible range) based beam diagnostics was proposed in 1973 and over around 50-years, have gathered a lot of attention due to some advantages like high light yield, simple experimental setup, possibility of working with different wavelengths. Dependence of the radiation yield and the degree of polarization of transition radiation on angle of incidence and angle of observation, beam energy and beam profile, target material and surface characteristics (e.g. roughness), wavelength of emitted radiation etc. continues to be the topic of numerous studies and the findings are exploited to improve OTR based beam diagnostic techniques.

Understanding of mechanism of formation of the transition radiation, its properties, and ways to flexibly shape it offers novel possibilities in beam diagnostics instrumentation as well as particle counters for future accelerators and colliders. Application of OTR for heavy ion beam diagnostics comes with its own set of opportunities and challenges.

One of the main characteristics of transition radiation is the high degree of polarization in the plane of observation. Interestingly, overall yield and degree of polarization is significantly different for rough targets. In addition to expected linearly polarized transition radiation in the plane of observation, a significant component of unpolarized radiation is reported with rough surface and non-relativistic ion beams.

A theoretical model and deeper understanding of OTR from rough surfaces looks a promising way forward to new beam diagnostic technique. This project aims to do that with experiments and simulations to verify this understanding and develop new insights. This project is jointly funded by STFC CDT LIV.INNO and GSI-FAIR, Germany. The work will be carried out at the Cockcroft Institute, U.K and GSI, Germany.