Materials Analysis Particle Probe (MAPP) diagnostic

Bryan R Heim, Purdue University

Abstract

Lithium conditioning of plasma-facing components surfaces (PFCs) has been implemented in the National Spherical Torus Experiment (NSTX) leading to improvements in plasma performance such as reduced D recycling and a reduction in edge localized modes (ELMs). Analysis of post-mortem tiles and offline experiments has identified interactions between Li-O-D and Li-C-O-D as binding channels for deuterium retention in ATJ graphite. The sensitivity to the chemical state of the PFCs and the correlation to plasma behavior motivates the use of an in-situ probe capable of measuring the surface chemistry state between plasma shots in NSTX. MAPP is a unique surface analysis diagnostic integrated into a tokamak allowing shot-to-shot chemical surface analysis of plasma materials interactions (PMI). For the first time, the possibility to correlate plasma performance to the plasma-material interface in the spatial scale of the material surface is now possible. Surface analysis techniques include: X-ray photoelectron spectroscopy (XPS), direct recoil spectroscopy (DRS), and thermal desorption spectroscopy (TDS), which probe the chemistry of the top surface layer (1-2 monolayers) and the near surface (5-10 nm) for chemical functionalities between Li-O-D and retention of hydrogen in a wide range of multi-component material matrices. Exposure of a maximum of four samples of various materials (C, Mo, Li-C, liquid Li, Pd) to a variety of NSTX plasma configurations enables the study of candidate PFCs materials. In-situ heating also allows for study of various thermal-driven phenomena. MAPP is equipped with a custom-designed remote diagnostic and data acquisition control system enabling remote access during experiments in NSTX. Integration of MAPP PFC surface chemistry with post-mortem sample analysis and off-line particle-beam surface interaction experiments coupled with computational modeling provides a targeted strategy to decipher mechanisms responsible for coupling of the evolving tokamak material surface and plasma edge behavior. This thesis summarizes the design, engineering, and initial calibration for the MAPP diagnostic and its coupling to the NSTX experimental campaign. MAPP and its possible use on other fusion devices is also discussed.

Degree

M.S.

Advisors

Allain, Purdue University.

Subject Area

Nuclear engineering|Materials science

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