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hicks_icc_2011_paper.pdf2011-08-26 13:42:26Nathaniel Hicks

A New Design of a Polarimeter for Non-invasive Internal Magnetic Field Measurements on the HIT-SI Spheromak

Author: Nathaniel K Hicks
Requested Type: Poster Only
Submitted: 2011-06-10 10:42:09

Co-authors: R. J. Smith, D. A. Ennis, C. J. Hansen, T. R. Jarboe, B. S. Victor, J. S. Wrobel, and the HIT-SI Team; J. Howard

Contact Info:
University of Washington
Box 352250
Seattle, WA   98105-2

Abstract Text:
The Helicity Injected Torus – Steady Inductive (HIT-SI) program investigates helicity injection current drive for magnetic confinement. The installation of a non-perturbative diagnostic of the internal magnetic field in HIT-SI discharges would allow the important ability to measure current-, q- and λ-profiles. Due to the lack of a neutral beam on HIT-SI and because of the relatively low magnetic field strength Btor ~ Bpol ~ 10-100 mTesla, polarimetry is more feasible than motional Stark effect measurements. The polarimeter diagnostic will introduce a probe beam at millimeter wavelengths, and the beam’s polarization is modified by the spheromak plasma as it propagates; measurement of this effect yields the density-weighted, line-integrated magnetic field parallel to the propagation. The diagnostic will also make an interferometric measurement of the electron density. Since the previous ICC workshop, it became clear that constraints on probe beam wavelength (due to increased plasma density in HIT-SI approaching 10^20 m^-3 and accompanying refractive effects) and on cost of the instrument would necessitate a new approach to the instrument. A novel design has therefore been developed that employs a single swept-frequency, backward wave oscillator radiation source (center frequency 300 GHz) and a single detector. The measurements will help to validate MHD codes running at the PSI-Center. This research is supported in part by an appointment to the U.S. Department of Energy Fusion Energy Postdoctoral Research Program administered by the Oak Ridge Institute for Science and Education.

Characterization: A3

Please place with other HIT-SI posters. Thank you.

University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011