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This content will become publicly available on March 9, 2019

Title: Improvements to the Ion Doppler Spectrometer Diagnostic on the HIT-SI Experiments

An Ion Doppler Spectrometer diagnostic system measuring impurity ion temperature and velocity on the HIT-SI and HIT-SI3 spheromak devices has been improved with higher spatiotemporal resolution and lower error than previously described devices. Hardware and software improvements to the established technique have resulted in a record 6.9 µs temporal and <=2.8 cm spatial resolution in the midplane of each device. These allow C III and O II flow, displacement, and temperature profiles to be simultaneously observed. With 72 fused-silica fiber channels in two independent bundles, and an f/8.5 Czerny-Turner spectrometer coupled to video camera, frame-rates of up to ten times the imposed magnetic perturbation frequency of 14.5 kHz were achieved in HIT-SI, viewing the upper 1/2 of the midplane. In HIT-SI3 frame-rates of up to eight times the perturbation frequency were achieved viewing both halves of the midplane. Biorthogonal Decomposition is used as a novel filtering tool, reducing uncertainty in ion temperature from <=13 to <=5 eV (with an instrument temperature of 8-16 eV), and uncertainty in velocity from <=2 to <=1 km/s. Doppler shift and broadening is calculated via the Levenberg-Marquart algorithm, after which errors in velocity and temperature are uniquely specified. Axisymmetric temperature profiles on HIT-SI3 for Cmore » III peaked near the inboard current separatrix at approximately 40 eV are observed. Axisymmetric plasma displacement profiles have been measured on HIT-SI3, peaking at approximately 6 cm at the outboard separatrix. Both profiles agree with the upper half of the midplane observable by HIT-SI. With its complete midplane view, HIT-SI3 has unambiguously extracted axisymmetric, toroidal current dependent rotation of up to 3 km/s. Analysis of the temporal phase of the displacement uncovers a coherent structure, locked to the applied perturbation. Previously described diagnostic systems could not achieve such results.« less
ORCiD logo [1] ; ORCiD logo [1] ;  [1] ; ORCiD logo [1]
  1. Univ. of Washington, Seattle, WA (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 89; Journal Issue: 3; Journal ID: ISSN 0034-6748
American Institute of Physics (AIP)
Research Org:
Univ. of Washington, Seattle, WA (United States). HIT-Group
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Ion Doppler Spectrometer; HIT-SI; Plasma Diagnostics; Spheromak
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1425255