Initial results of tests of depth markers as a surface diagnostic for fusion devices

The Accelerator-Based In Situ Materials Surveillance (AIMS) diagnostic was developed to perform in situ ion beam analysis (IBA) on Alcator C-Mod in August 2012 to study divertor surfaces between shots. These results were limited to studying low-Z surface properties, because the Coulomb barrier precludes nuclear reactions between high-Z elements and the ∼1 MeV AIMS deuteron beam. In order to measure the high-Z erosion, a technique using deuteron-induced gamma emission and a low-Z depth marker is being developed. To determine the depth of the marker while eliminating some uncertainty due to beam and detector parameters, the energy dependence of the ratio of two gamma yields produced from the same depth marker will be used to determine the ion beam energy loss in the surface, and thus the thickness of the high-Z surface. This paper presents the results of initial trials of using an implanted depth marker layer with a deuteron beam and the method of ratios. First tests of a lithium depth marker proved unsuccessful due to the production of conflicting gamma peaks, among other issues. However, successful trials with a boron depth marker show that it is possible to measure the depth of the marker layer with the method of gamma yield ratios.United States. Department of Energy. (grant number DE-FG02-94ER54235, cooperative agreement number DEFC02-99ER54512

Development and testing of an in situ method of ion beam analysis for measuring high-Z erosion inside a tokamak using an AIMS diagnostic

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 157-163).While many ex situ measurements exist to measure plasma-facing component (PFC) surfaces of materials extracted from tokamaks, developing a deeper understanding of the dynamics of erosion, redeposition, and fuel retention in these surfaces will require in situ measurements. A first-of-a-kind technique, Accelerator-Based In-Situ Materials Surveillance (AIMS), was developed for this purpose and first demonstrated on Alcator C-Mod to study divertor surfaces with shot-by-shot resolution [1]. However, the original AIMS methods are not applicable to studying the erosion of bulk, high-Z PFCs like molybdenum and tungsten. Thus, a new method of ion beam analysis (IBA) has been developed to expand the capabilities of AIMS to directly measure this high-Z bulk erosion. This new method, called DEA (Depth markers for Evaluating high-Z materials with AIMS), combines the traditional IBA technique of particle-induced gamma emission (PIGE) with implanted depth markers.The implanted markers enable the study of bulk material by providing a reference to the surface that can be monitored for erosion and redeposition. Implanting the marker eliminates the need for specially-manufactured "marker tiles" formed by deposited layers that can delaminate and otherwise fail under operational conditions. Two variations of this method were developed: ex situ DEA (eDEA) and in situ DEA (iDEA). Both use PIGE spectroscopy with implanted markers, but they take advantage of different features in gamma production cross sections to analyze data. eDEA, which has shown promising results in ex situ analysis of materials exposed in a tokamak, can also be used to validate the use of depth markers. iDEA provides AIMS with the ability to measure in situ high-Z bulk erosion. As part of this thesis, the following ex situ experiments have been carried out to assess the viability of these techniques.eDEA samples with implanted depth markers have been studied after plasma exposure on the Material and Plasma Evaluation System (MAPES) in the Experimental Advanced Superconducting Tokamak (EAST). Stability of the marker to temperature excursions was studied by exposing samples to temperatures from 200 to 1000C for times from 1 to 24 hours. iDEA samples were implanted at different depths to determine the sensitivity of the technique to depth. Two simulations were developed to allow interpretation of the experimental data and to test the sensitivity, with initial studies showing a match between predicted and experimental results. eDEA measured erosion of 42.0 23.5 nm on one sample exposed in EAST, and iDEA depth markers were located with 40 nm of accuracy. These results show that DEA, as a part of an AIMS experiment, has the appropriate resolution to monitor surfaces inside a tokamak for time-resolved bulk erosion.by Leigh A. Kesler.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineerin