On the measurement of poloidal field distributions in Tokamaks by far-infrared polarimetry

Kunz, W.; Dodd, Gregory C.

doi:10.1088/0032-1028/20/2/009

Cited by 24 publications

(8 citation statements)

References 4 publications

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“…In practice, it is found useful to modulate the intensity sensed by the detector at some known frequency to facilitate detection and enhance signal-to-noise ratios. This is accomplished either by modulating I o in time [40], or by rocking the polarization angle of the incident EM wave, which generates a sinusoidal temporal modulation of the intensity transmitted by the polarization analyzer [42], [43]. Both of these concepts will be discussed in detail in Section 3.2.1.…”

Section: Polarimetrymentioning

confidence: 99%

“…The rocking polarization method (see Figure 3.5) was first demonstrated by Kunz [42]. Extensive systems based on this technique (and incorporating simultaneous interferometric measurements) have been assembled on the ISX-B tokamak [46] [43] and on TEXT tokamak [47].…”

Section: Polarimetrymentioning

confidence: 99%

“…Faraday rotation induced by the plasma generates a signal at the modulation frequency. The amount of Faraday rotation is calculated from the amplitude of the signal at the modulation frequency [42], [43]. Because this method does not require two beams to be combined on a polarizing beam splitter, this method is inherently less sensitive to refractive effects.…”

Section: Amplitude Polarimetrymentioning

confidence: 99%

“…Because this method does not require two beams to be combined on a polarizing beam splitter, this method is inherently less sensitive to refractive effects. An initial drawback was the 10% transmission factor of the ferrite modulator [42]; however, development at Oak Ridge National Laboratory [43] resulted in a more acceptable transmission factor of ~ 80%. The higher transmission was obtained for A = 447 nm radiation.…”

Section: Amplitude Polarimetrymentioning

confidence: 99%

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Far-infrared polarimetry/interferometry for poloidal magnetic field measurement on ZT-40M

Erickson¹,

Forman²,

Jahoda³

1986

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The measurement of internal magnetic field profiles may be a very important step in the understanding of magnetic confinement physics issues. The measurement of plasma-induced Faraday rotation is one of the more promising internal magnetic field diagnostics, This thesis describes the development of a heterodyne polarimeter/interferometer for internal poloidal magnetic field measurement on ZT-40M. Heterodyne techniques were employed because of the insensitivity to spurious signal amplitude changes that cause errors in other methods. I am grateful to the ZT-40M program management for the contribution of machine access (as poor as it was) and funding, and for their patience during the diagnostic development. I would also like to thank the ZT-40M team for their interest, and for supplying some of the data that is presented in this thesis. I appreciate the friendship and support of the people I have come to know at Los Alamos. Finally, I would like to thank my wife, Laura, for typing the text of this thesis, and Dr. Cris W. Barnes for his help in the preparation of this document. Ill 4.11 Baseline with Four-Signal Technique 112 4.12 Heterodyne Polarimeter on ZT-40M 116 4.13 ZT-40M Interferometer 4.14 Simultaneous Configuration 119 4.15 Revised Simultaneous Configuration 122 4.16 Two-Chord Simultaneous Configuration 123 4.17 Preamplifier Circuit for GaAs Photoconductor 124 4.18 Method for Calculating Carrier-Signal Phase 128 5.1 Polarimetric Measurements Indicating Sensitivity Problems 134 5.2 Theoretical Beam Profiles for Geometry of ZT-40M 139 5.3 Setup for Beam Propagation Measurements 140 5.4 Measured Intensity Profiles for Geometry of ZT-40M 141 5.5 Crossed Polarizer Test Setup 142 5.6 Polarization Azimuth Rotation for Bare Metal, Quartz, and Threaded Tubulations 144 5.7 Reflectivities and Phase Difference for s and p Polarizations for Grazing Angles of Incidence 146 5.8 Polarization Rotation vs. Incident Azimuth 5.9 Quartz Inserts after Removal from ZT-40M 5.10 Profile of Metallic Deposition on Quartz 5.11 Polarimetric Phase for ZT-40M Discharges with Bare Tubulations, Bypassing Torus, and with Threaded Inserts 6.1 Interferometric Measurement with Two-Signal Technique 6.2 Example of Interferometric Measurement in Simultaneous Configuration 6.3 Central-and Edge-chord-averajred Densities 6.4 Examples of Density Sawtooth Oscillations 6.5 Density of Ramped (70 kA to 170 kA) Discharge Compared to Standard 170 kA Discharge 165 6.6 Carrier Signal Measured by the Polarimeter 166 6.7 Toroidal Current and Faraday Rotation for a Design-Mode Discharge 168 7 List of Tables 1.1 Relative Merits of Measurement Techniques 4.1 Laser Gases 6.1 Calculated Faraday Rotation Levels for Various Profiles

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Section: Polarimetrymentioning

confidence: 99%

Section: Polarimetrymentioning

confidence: 99%

Section: Amplitude Polarimetrymentioning

confidence: 99%

Section: Amplitude Polarimetrymentioning

confidence: 99%

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Far-infrared polarimetry/interferometry for poloidal magnetic field measurement on ZT-40M

Erickson¹,

Forman²,

Jahoda³

1986

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“…For the measurements the polarization modulation method described in Ref. [4] was used: A ferrite modulator (FM) consisting of a ferrite disk in the alternating magnetic field of an air coil causes an oscillating rotation (amplitude a m ) of the plane of polarization. An additional rotation a pl is caused by the Faraday effect in the plasma due to the poloidal magnetic field.…”

Section: Experimental Arrangementmentioning

confidence: 99%

First measurement of poloidal-field-induced Faraday rotation in a tokamak plasma

Kunz

Tfr

1978

Nucl. Fusion

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Faraday rotation measurements using a ferrite modulation technique were performed on one channel of the 337 μm-interferometer on TFR. The experiment is intended as a preparatory step towards poloidal-field determination on the basis of the Faraday effect in a multi-channel configuration. The technical feasibility of precise Faraday rotation measurements under machine conditions is demonstrated. The measured rotation is unambiguously due to the poloidal magnetic field and agrees fairly with what can be estimated.

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Spectroscopic Plasma Diagnostics

Drawin

1983

Atomic and Molecular Physics of Controlled Thermonuclear Fusion

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On the measurement of poloidal field distributions in Tokamaks by far-infrared polarimetry

Cited by 24 publications

References 4 publications

Far-infrared polarimetry/interferometry for poloidal magnetic field measurement on ZT-40M

Far-infrared polarimetry/interferometry for poloidal magnetic field measurement on ZT-40M

First measurement of poloidal-field-induced Faraday rotation in a tokamak plasma

Spectroscopic Plasma Diagnostics

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