External proton beam analysis of plasma facing materials for magnetic confinement fusion applications

摘要

A 1.7MV tandem accelerator was reconstructed and refurbished for this thesis and for surface science applications at the Cambridge laboratory for accelerator study of surfaces (CLASS). At CLASS, an external proton beam set-up was designed and constructed to perform in-air ion beam analysis on plasma facing divertor tiles from the Alcator C-Mod tokamak. A Particle Induced Gamma Emission (PIGE) technique was developed for boron depth profiling. In addition, Particle Induced X-ray Emission (PIXE) was implemented and used for a comprehensive study of poloidal tungsten migration in the C-Mod divertor. A novel PIGE technique was developed for measuring depth profiles of boron deposition on C-Mod tile surfaces. Boron (B) is regularly deposited on C-Mod tiles to improve plasma performance. This technique is therefore useful for studying the interaction of B with plasma facing components (PFC) to develop a better understanding of the effects of B in Alcator C-Mod. The technique involves taking multiple PIGE yield measurements of a single sample while changing the beams path-length through the air to vary the energy of the beam incident on the sample. A numerical code was written to deconvolve boron depth profiles from these gamma yields by exploiting the sharply peaked cross section of the '0B(p, ay)7Be resonance reaction. Simulations demonstrate that this code converges to the expected results. Preliminary measurements of C-Mod tiles were performed using the external proton beam to induce 429keV gamma emission from the 10B(p, ay)7Be reaction which was measured, using a Sodium Iodide (Nal) scintillation detector.