Fuel retention measurements in Alcator C-Mod using accelerator-based in situ materials surveillance

Abstract

This paper presents the first in-situ time-and space-resolved measurements of deuterium (D) fuel retention in plasma-facing component (PFC) surfaces using Acceleratorbased In-situ Materials Surveillance (AIMS) on the Alcator C-Mod tokamak. AIMS is a novel in-situ materials diagnostic technique based on the spectroscopic analysis of nuclear reaction products induced in PFC surfaces using an ∼MeV beam of deuterons from a compact linear accelerator in between plasma shots. AIMS measurements of D retention on inner wall PFCs were acquired during diverted and limited plasma operations and during wall conditioning experiments. Intershot measurements demonstrate the local erosion and codeposition of boron films on PFC surfaces with a constant D/B ratio. This is consistent with previous results suggesting that D codeposition with boron is insufficient to account for the net retention observed in Alcator C-Mod. Changes in deuterium concentration during boronization, electron cyclotron and glow cleanings were also measured.

Alcator C-Mod: research in support of ITER and steps beyond

“…In addition, the AIMS measurements indicate that the plasma does not deplete retained deuterium from the boron films over the course of a run day. This provides additional evidence that retention in boron films cannot sufficiently explain the net fuel retention observed on Alcator C-Mod, as there is insufficient atomic capacity for deuterium storage [70].…”

20 years of research on the Alcator C-Mod tokamak

“…54 Early results have proven the principle of the technique and shown that measurements could be routinely made between shots. [55][56][57] C. Divertor regimes and detachment physics Meeting the challenges of divertor power handling and erosion require better understanding of the underlying physics, through which improved designs and operating regimes can be achieved. The operating point of the divertor depends in large measure on the balance between parallel and perpendicular transport.…”

Application of Ion Beam Analysis in Studies of First Wall Materials in Controlled Fusion Devices

“…The latter involves chambers for in-situ experiments (e.g., exposure to plasma, implantation, thermal treatment) with simultaneous analyses to determine the dynamics of processes without breaking vacuum; the research challenges have been addressed in [45]. In-situ IBA, i.e., inside a fusion device, has been discussed for a long time and, once, it has been demonstrated in Alcator-C Mod [71]. However, such an approach in a reactor-class machine will not be possible.…”