Special behavior of alkali beam emission spectroscopy in low-ion-temperature plasma

TL;DR

This paper investigates the unique behavior of alkali beam emission spectroscopy in low-ion-temperature plasmas using synthetic diagnostics, revealing distinctive emission features and plasma interactions in low-density, low-temperature conditions.

Contribution

It introduces a detailed analysis of BES in low-ion-temperature plasma regimes using the RENATE-OD synthetic diagnostic code, highlighting behaviors not previously explored.

Findings

BES shows unusual emission tendencies in low-ion-temperature, low-density plasmas.

The relation between beam energy and plasma penetration differs in these conditions.

Unique emission features are facilitated by low plasma density.

Abstract

Beam emission spectroscopy (BES) is a powerful plasma diagnostic method especially suited for the measurement of plasma density and its fluctuations. As such, synthetic BES codes are regularly used to aid the design or utilization of these diagnostic systems. However, synthetic diagnostics can also be used to study the method in previously not yet explored operational conditions. This paper presents such an analysis utilizing the RENATE-OD synthetic diagnostic code for a hypothetical alkali BES system on the HSX stellarator. HSX is a device featuring an unusual operating regime in the world of fusion devices due to the low ion temperature and low plasma density. It was found that BES shows unusual tendencies in these conditions. The relation between beam energy and plasma penetration in low-ion-temperature plasma, together with unique emission features facilitated by low-density plasma, and the underlying reasons behind these features are explored in this paper.