Optical transition radiation diagnostics for low energy ion beams

跃迁辐射是指当带电粒子在光学不均匀区域(如具有不同介电性质的两种介质之间的界面)运动时所发射的电磁辐射。跃迁辐射在高能粒子探测、相干辐射源、束流诊断等方面都有应用。随着材料科学和纳米技术的进步，最近出现了一些利用人工工程材料来改变跃迁辐射性质的研究。电荷分布诊断是加速器运行和优化的基本诊断要求，通常被称为横向面上的束流分布和纵向面上的束流监测。目前已有几种已建立的方法，如二次电子监测器(SEM)栅格和束流诱导荧光(BIF)，用于横向束流轮廓测量，然而，随着加速器和束流动力学的快速发展，这些方法在重离子束背景下的快速难辐射诊断中的适用性受到质疑。它们受到测量轮廓的分辨率、信号产生过程的基本限制以及测量设备对光束轮廓的影响的限制。基于光学跃迁辐射的光束诊断技术于1973年提出，近50年来，由于具有光产额高、实验装置简单、可在不同波长下工作等优点，引起了人们的广泛关注。辐射产额和跃迁辐射的偏振度与入射角和观察角、束流能量和束流分布、目标材料和表面特性(例如粗糙度)、发射辐射波长等的依赖关系仍然是许多研究的主题，这些发现被用来改进基于OTR的束流诊断技术。了解跃迁辐射的形成机制、性质和灵活成形它的方法，为未来的加速器和对撞机的束流诊断仪器和粒子计数器提供了新的可能性。OTR在重离子束诊断中的应用也带来了一系列的机遇和挑战。跃迁辐射的一个主要特点是在观测平面内偏振度很高。有趣的是，总体产量和极化程度对于粗糙的目标来说是显著不同的。除了观测平面上预期的线偏振跃迁辐射外，粗糙表面和非相对论离子束还报告了非偏振辐射的一个重要组成部分。理论模型的建立和对粗糙表面光学共振的深入理解为新的束流诊断技术提供了一条很有前途的发展方向。该项目旨在通过实验和模拟来验证这一理解并开发新的见解。该项目由STFC CDT LIV.INNO和德国GSI-FIRE联合资助。这项工作将在英国的考克罗夫特研究所和德国的GSI进行。

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.