Validating neutral-beam current drive simulations in the TJ-II stellarator

TL;DR

This study validates neutral-beam current drive simulations in the TJ-II stellarator by comparing experimental results with theoretical models, highlighting good agreement for one beam direction and discrepancies for the other.

Contribution

It provides a validation of current drive simulations in stellarators using experimental data and analytical modeling, with insights into the accuracy of predictions for different beam configurations.

Findings

Good agreement between simulation and experiment for NBI2 current.

Discrepancy where NBI1 current is less than half predicted.

Discussion of potential reasons for the mismatch.

Abstract

In this paper, we analyze the results of neutral-beam current drive (NBCD) experiments, performed in the TJ-II stellarator, with the aim of validating the theoretical predictions. Both parallel and anti-parallel injection with respect to the magnetic field were explored using co (NBI1) and counter (NBI2) beams at different injected beam power and plasma densities. The fast-ion current driven by both beams was simulated with the Monte Carlo code ASCOT and the electron response to the fast-ion current was calculated analytically using a model valid for an arbitrary magnetic configuration and a low collisionality plasma. The model reproduces with rather good agreement the toroidal current measured in NBI2 plasmas while the current driven by NBI1 is less than half the predicted one. Possible reasons for this discrepancy are discussed.