Spectro-polarimetrc optical systems for imaging plasma internal fields, structures and flows

Abstract

Spectro-polarimetric imaging systems have opened new and better ways to study the spatio-temporal behaviour of plasma properties including current distribution, pedestal fields and the velocity distribution function of radiating species from the plasma edge to the core. Using spatial-heterodyne polarimetric techniques, these coherence-imaging (CI) systems have been deployed for motional Stark effect (MSE) imaging and charge-exchange Doppler imaging (CXRS) on KSTAR and ASDEX-Upgrade, and for passive Doppler spectroscopy of the plasma edge on DIII-D and MAST. They have also been used for Doppler imaging of low-temperature argon discharges on the linear mirror device MAGPIE at the ANU, including synchronous Doppler imaging of flow vortices associated with low frequency instabilities. We describe the diagnostic technologies, discuss the results and comparisons with simple models, and consider new applications and future developments.

Stokes-Doppler coherence imaging for ITER boundary tomography

“…For Doppler broadened and shifted emission spectra, interferometric measurements of the optical coherence (fringe contrast and phase) deliver projections of the brightnessweighted ion temperature and flow speed. For a snapshot spatial-heterodyne imaging polarization interferometer, the brightness at position (x, y) in the image plane is given by 5,7…”

“…1,2 Similar techniques have been applied to polarized multiplets to image the magnetic field pitch angle in tokamaks through the motional Stark effect. [3][4][5] We combine these ideas to propose a Stokes-Doppler coherence-imaging camera to map the full Stokes vector of Zeeman-split impurity lines in the tokamak scrape-off-layer (SOL) and divertor.…”

A photoelastic-modulator-based motional Stark effect polarimeter for ITER that is insensitive to polarized broadband background reflections

“…In Sections III C and III D the sinusoidal filter and polarization encoding are established within a single system. Knowledge of the spectrum is not required for these measurements as its effect is limited to the amplitudes expressed in Equations (21) and (22), which are common to the encoding Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 130.56.97.48 On: Mon, 19 Sep of both s 1 and s 2 .…”

“…15 An alternative to PEM-based MSE polarimetry has been proposed recently. 16,17,21 Imaging motional Stark effect (IMSE) observes light from the full multiplet, achieving spectral discrimination and high net polarization fraction with a birefringent sinusoidal interference filter. This approach is amenable to two dimensional imaging of the beam emission as there is no need to precisely track the beam Doppler shift.…”

Coherence-imaging spectroscopy for 2D distribution of ion temperature and flow velocity in a laboratory magnetosphere

“…The spectrometer obtains the one-dimensional (1D) spatial profile of temperatures and velocities from the Doppler effect. Based on the optical coherence effect, 1,2 coherence-imaging spectroscopy (CIS) enables us to obtain two-dimensional (2D) spatial images of temperatures and velocities in plasmas. Recently, the CIS has been successfully demonstrated on MAGPIE linear plasmas, 3 MAST spherical tokamak plasmas, 4,5 and DIII-D tokamak plasmas.…”