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Title: Correlation polarimetry for broadband magnetic fluctuation measurements

Journal Article · · Review of Scientific Instruments
DOI:https://doi.org/10.1063/1.5038832· OSTI ID:1609214
 [1];  [1];  [1]
  1. Univ. of California, Los Angeles, CA (United States)
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Correlation techniques have been successfully utilized for plasma diagnostics like electron cyclotron emission to reduce measurement noise. Herein we present the first application of such a technique to Faraday-effect polarimetry measurements on the Madison Symmetric Torus (MST). The MST far infrared (FIR) interferometer-polarimeter diagnostic utilizes 11 vertical chords with a chord separation of 7-8 cm and a heterodyne detection system for fluctuation measurements up to several hundred kHz. The planar-diode mixers viewing each chord represent independent noise sources; modifying the optical setup so that two different mixers view the same chord allows cross correlation between the two independent signals to reduce the noise floor in fluctuation measurements. In this manner, the noise floor in both interferometry and polarimetry measurements in reversed-field pinch discharges has been reduced by a factor of 20-30. The correlation polarimeter provides a sensitive measurement of broadband magnetic fluctuations.

Research Organization:
Univ. of Wisconsin, Madison, WI (United States); Univ. of California, Los Angeles, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Grant/Contract Number:
FC02-05ER54814; FG02-01ER54615
OSTI ID:
1609214
Alternate ID(s):
OSTI ID: 1471801
Journal Information:
Review of Scientific Instruments, Vol. 89, Issue 10; Conference: 22.Topical Conference on High Temperature Plasma Diagnostics, San Diego, CA (United States), 15-19 Apr 2018; ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English

References (8)

An upgraded interferometer-polarimeter system for broadband fluctuation measurements journal August 2016
Laser polarimetric measurement of equilibrium and fluctuating magnetic fields in a reversed field pinch (invited) journal March 2003
Upgrade of far-infrared laser-based Faraday rotation measurement on MST journal October 2010
Core temperature fluctuations and related heat transport in the Texas Experimental Tokamak‐Upgrade journal March 1995
Study of plasma density fluctuations by the correlation of crossed CO2 laser beams journal January 1980
Dual mode (ordinary–extraordinary) correlation reflectometry for magnetic field and turbulence measurements (invited) journal January 2001
High-frequency fluctuation measurements by far-infrared laser Faraday-effect polarimetry-interferometry and forward scattering system on MST journal November 2014
A far-infrared ‘polari-interferometer’ for simultaneous electron density and magnetic field measurements in plasmas journal December 1978

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Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
Instruments & Instrumentation
Physics