Onion-peeling inversion of stellarator images

TL;DR

This paper introduces an onion-peeling method to reconstruct the emissivity profile of stellarator plasmas from 2D images, assuming uniform emissivity within flux surface layers, enabling better plasma diagnostics.

Contribution

It develops a novel linear inversion technique for stellarator imaging that leverages flux surface topology and pixel line-of-sight integration.

Findings

Successfully applied to CNT stellarator images

Revealed emissivity profiles consistent with plasma conditions

Provides a new diagnostic tool for stellarator research

Abstract

An onion-peeling technique is developed for inferring the emissivity profile of a stellarator plasma from a two-dimensional image acquired through a CCD or CMOS camera. Each pixel in the image is treated as an integral of emission along a particular line-of-sight. Additionally, the flux surfaces in the plasma are partitioned into discrete layers, each of which is assumed to have uniform emissivity. If the topology of the flux surfaces is known, this construction permits the development of a system of linear equations that can be solved for the emissivity of each layer. We present initial results of this method applied to wide-angle visible images of the CNT stellarator plasma.