Adjoint Monte Carlo Simulation of Fusion Product Activation Probe Experiment in ASDEX Upgrade tokamak

TL;DR

This paper presents the first numerical analysis of fusion product flux measurements in the ASDEX Upgrade tokamak using adjoint Monte Carlo simulations, achieving good agreement with experimental data and proposing an optimized probe orientation.

Contribution

It introduces the first application of adjoint Monte Carlo calculations to analyze fusion product flux measurements in a tokamak experiment.

Findings

Numerical and experimental flux values agree within a factor of two.

The analysis demonstrates the effectiveness of adjoint Monte Carlo methods for fusion diagnostics.

An optimized probe orientation could enhance flux measurement coverage.

Abstract

The activation probe is a robust tool to measure flux of fusion products from a magnetically confined plasma. A carefully chosen solid sample is exposed to the flux, and the impinging ions transmute the material making it radioactive. Ultra-low level gamma-ray spectroscopy is used post mortem to measure the activity and, thus, the number of fusion products. This contribution presents the numerical analysis of the first measurement in the ASDEX Upgrade tokamak, which was also the first experiment to measure a single discharge. The ASCOT suite of codes was used to perform adjoint/reverse Monte Carlo calculations of the fusion products. The analysis facilitates, for the first time, a comparison of numerical and experimental values for absolutely calibrated flux. The results agree to within a factor of about two, which can be considered a quite good result considering the fact that all features of the plasma cannot be accounted in the simulations. Also an alternative to the present probe orientation was studied. The results suggest that a better optimized orientation could measure the flux from a significantly larger part of the plasma.