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Using Doppler Spectroscopy of Lithium Ions to Characterize Plasma Dynamics in the Lithium Tokamak Experiment

Author: Theodore M. Biewer
Requested Type: Poster Only
Submitted: 2012-12-07 08:30:14

Co-authors: D.P. Boyle, T.K. Gray, R. Kaita, R. Maingi, R. Majeski

Contact Info:
Oak Ridge National Laboratory
1 Bethel Valley Road
Oak Ridge, TN   37831
USA

Abstract Text:
There has been a long-standing collaboration between ORNL and PPPL on edge and boundary layer physics. As part of this collaboration, ORNL has a large role in the instrumentation and interpretation of edge physics in the Lithium Tokamak Experiment (LTX). In particular, a high-resolution spectroscopy diagnostic has been designed and is undergoing staged implementation on LTX. Here we present initial results (from 2012) of passively measured lithium charge exchange emission at 5166.89 Å in LTX, and show the expected measurement improvement from a recently completed upgrade to the diagnostic (to be utilized in 2013). Preliminary measurements have been made in transient LTX plasmas with plasma current, Ip = 40 – 65 kA, ohmic heating power, Poh ~ 0.3 MW and discharge lifetimes of 10 – 30 ms. Doppler spectroscopy measurements are made with a short focal length spectrometer and optics similar to the Edge Rotation Diagnostic (ERD) on NSTX. The diagnostic is being upgraded to 17 toroidal sightlines (from 6) and 6 to 9 up-down symmetric poloidal sightline pairs (from 5 pairs). Radial coverage of the poloidal array will extend between 0.2<r/a<0.95, while the toroidal array will cover 0<r/a<0.7. Simulations suggest that line-of-sight measurements from the upgraded diagnostic can be inverted to yield local profile values of Ti, vϕ, vθ and nLi. Inversions rely on accurate equilibrium reconstructions, which are expected from recently completed repair/upgrade to magnetic diagnostics and due to the adaptation of the LRDFIT code to LTX. With the equilibrium magnetic field reconstructions and the estimation of local plasma parameters from this diagnostic, under the assumption of force balance the radial electric field profile, Er, can be calculated. The effect of lithium on the Er profile, as well as the fundamental plasma parameters, is a major topic of interest for LTX and the plasma physics community. Preliminary results will be presented, and a general summary of the status of ORNL collaborations with LTX will be given.

This work was supported by the US. D.O.E. contracts DE-AC05-00OR22725 and DE-AC02-09CH11466.

Characterization: 3.0

Comments:
Group with other LTX presentations.