Coherence Imaging of Flows in the DIII‐D Divertor

Abstract

Various spatial heterodyne polarization interferometers for spectrally-resolved optical imaging of edge and core parameters in high temperature magnetized plasmas are described. Applications for such "coherence imaging" (CI) systems include imaging motional Stark effect and Zeeman effect polarimetry for determination of the magnetic field pitch angle, and passive and active (charge exchange recombination spectroscopy -CXRS) Doppler imaging of plasma temperature and flow. In this paper we describe spatial heterodyne coherence imaging systems and present first results of Doppler flow imaging in the DIII-D divertor.Instruments have been installed for imaging flows in the divertor and scrape-off-layer in the DIII-D tokamak and also for Doppler imaging on the H-1 heliac [1]. In the former case, single snapshot interferometric images of the plasma in CII 514nm, and CIII 465nm emission have been demodulated to obtain flow and ion temperature projections in both the scrape-off-layer and divertor. Flow field amplitudes in the divertor are found to be broad agreement with UEDGE modeling [2], and point the way towards experiments that address important divertor transport issues in future.

Doppler coherence imaging and tomography of flows in tokamak plasmas (invited)

“…6,7 The interferogram can be demodulated and the local fringe amplitude and phase compared with the properties of a set of reference fringes. 5 Carbon ion flow measurements based on multiple discrete channel visible Doppler spectroscopy have also been reported previously. 8,9 We have recently deployed snapshot systems for Doppler imaging the emission from the CII 514 nm and CIII 465 nm multiplets originating in the divertor and SOL regions of the DIII-D tokamak.…”

“…While the optical system design and instrument response have been discussed in greater detail elsewhere, 5 we here summarize the key system features as they pertain to imaging measurements of the C2+ multiplet at 465 nm in the region of the DIII-D divertor.…”

“…The standard approach makes use of a grating spectrometer that disperses the spectrum in one spatial dimension and reserves the other to obtain a 1D spatial section of the region of interest. 4,5 In its simplest form, a polarization interferometer consists of a birefringent delay plate of suitable thickness sandwiched between crossed or parallel polarizers, combined with an optical interference prefilter to isolate the spectral features of interest. The power of both active and passive 2D optical imaging systems to reveal new physics has been demonstrated recently by a number of authors.…”

Scrape-Off-Layer Flow Studies in Tokamaks: Final Report of LDRD Project 09-ERD-025

“…Development/implementation/data for FTS system in DIII-D The LDRD-supported installation of the FTS system in DIII-D is described in detail in the attached publications [2,3], where the initial data obtained are also shown. The main purpose of this report is to highlight the most recent data and model comparisons that were presented at the APS-DPP Annual meeting in November 2012 [4] and are being written up for publication.…”

“…This "flow image" represents a line-averaged measurement of the C +2 flow velocity towards (or away from) the camera, weighted by the C +2 emissivity. Given precise knowledge of the camera location and magnetic geometry, the flow inside the plasma is tomographically reconstructed from the flow image [2][3]. This final reconstruction represents a poloidal cut of the C +2 flow in the plasma.…”