Application of a digital phase comparator technique to interferometer data

Jiang, Yong; Brower, D. L.; Zeng, Lijiang; Howard, J.

doi:10.1063/1.1147765

Cited by 57 publications

(42 citation statements)

References 3 publications

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“…The signal, which is measured at the difference frequency of the lasers, is then digitized and the phase computed using a digital phase comparator technique. 23 A third reference beam is required to obtain simultaneous density information. However, the system as presently configured is limited to two beams.…”

Section: Methodsmentioning

confidence: 99%

Measurement of current profile dynamics in the Madison Symmetric Torus

et al. 2004

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The current profile and core magnetic field fluctuation amplitudes in a reversed-field pinch are measured by using a high-resolution polarimetry–interferometry system. This paper presents data showing a redistribution of the current during a sawtooth crash. Also, the core magnetic field fluctuation amplitude is observed to increase at a sawtooth crash consistent with the idea of nonlinearly driven dynamo current. In addition, the parallel current density increases in the outer region of the plasma during auxiliary pulsed parallel current drive. This was expected, as the external application of an edge parallel electric field is designed to flatten the current profile providing an equilibrium closer to the minimum energy Taylor state. However, the current density also increases in the core, relative to standard plasmas. This increase can be explained by a reduction of the dynamo (anti)current drive in the core that should accompany the measured reduction of magnetic fluctuations and by a drop in resistivity caused by the increased confinement of fast electrons.

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Section: Methodsmentioning

confidence: 99%

Measurement of current profile dynamics in the Madison Symmetric Torus

et al. 2004

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“…That is caused by the misalignment between the rotor axis and the grating. 12 To improve the resolution, it is necessary to replace the grating or to adopt a twin laser system. Figure 4 shows measurement results of the polarimeter and the interferometer along the plasma center chord.…”

Section: Resultsmentioning

confidence: 99%

Cotton-Mouton polarimeter with HCN laser on CHS

Akiyama

Kawahata

Ito

et al. 2006

Review of Scientific Instruments

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Polarimeters based on the Cotton-Mouton effect hold promise for electron density measurements. We have designed and installed a Cotton-Mouton polarimeter on the Compact Helical System. The Cotton-Mouton effect is measured as the phase difference between probe and reference beams. In this system, an interferometric measurement can be performed simultaneously with the same probe chord. The light source is a HCN laser ͑wavelength of 337 m͒. Digital complex demodulation is adopted for small phase analysis. The line averaged density evaluated from the polarimeter along a plasma center chord is almost consistent with that from the interferometer.

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“…5 In Figs. 4͑a͒ and 4͑b͒, the time trace and Fourier transform of the filtered signal wave form is shown for a HSX interferometer chord.…”

Section: Phase Detection Data Acquisition and Signal Processingmentioning

confidence: 99%

“…Second, implementation of digital techniques can be employed to reduce the time response to a few microseconds. 5 In this approach, the filtered reference and signal wave forms at 750 kHz are directly digitized and the phase information extracted via use of software-based algorithms. This is referred to as the digital phase comparator ͑DPC͒, which is capable of achieving 4 s time response.…”

Section: Phase Detection Data Acquisition and Signal Processingmentioning

confidence: 99%

Multichannel interferometer system for the helically symmetric experiment

Brower

Deng

Ding

et al. 2001

Review of Scientific Instruments

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A multichannel millimeter-wave interferometer system has been designed, fabricated and installed on the helically symmetric experiment ͑HSX͒, located at the University of Wisconsin, Madison. The interferometer system will view the plasma cross section along nine adjacent chords with 1.5 cm spacing. With this arrangement, coverage will span from the low-field side plasma scrape-off layer to well past the magnetic axis. For the plasma densities anticipated on HSX, a solid-state source operating at 288 GHz will be utilized. At this frequency refraction will be manageable, being less than the channel spacing. The source will be bias-tuned and modulated with a sawtooth wave form at 750 kHz in order to generate the intermediate frequency necessary for the heterodyne detection scheme. The signals will be measured using Schottky-diode corner-cube mixers. The interferometer will have sensitivity n e dlϷ8ϫ10 11 cm Ϫ2 , being able to measure density changes Ͻ1%. Initially, the phase will be evaluated using analog electronics with bandwidth Ͻ10 kHz providing real-time line-integrated output. A digital phase comparator scheme will also be implemented whereby the measured wave forms are directly digitized and the phase evaluated using a software-based algorithm. This will increase the time response up to the modulation frequency of 750 kHz. Improved time response will permit measurement of high-frequency density fluctuations along with ''fast changes in'' the equilibrium profile.

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Application of a digital phase comparator technique to interferometer data

Cited by 57 publications

References 3 publications

Measurement of current profile dynamics in the Madison Symmetric Torus

Measurement of current profile dynamics in the Madison Symmetric Torus

Cotton-Mouton polarimeter with HCN laser on CHS

Multichannel interferometer system for the helically symmetric experiment

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