Faraday rotation densitometry for Large Helical Device

Akiyama, Tsuyoshi; Sato, E.; Nozawa, Takayuki; Tsuji‐Iio, S.; Shimada, Ryuichi; Murayama, H.; Nakayama, Keiichi I.; Okajima, S.; Tanaka, K.; Watanabe, K. Y.; Tokuzawa, T.; Kawahata, K.

doi:10.1063/1.1321742

Cited by 15 publications

(6 citation statements)

References 5 publications

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“…Single and multichannel systems have been developed and employed ͑with varying degrees of success͒ on the ZT-40M reversedfield pinch, 7 RTP tokamak, 8,9 LHD stellarator, 10 and a field reversed configuration. 11 However, the potential for high time response has never before been exploited to investigate a͒ Electronic mail: brower@mail.utexas.edu fast changes to equilibrium profiles or broadband magnetic fluctuations.…”

Section: Introductionmentioning

confidence: 99%

Laser polarimetric measurement of equilibrium and fluctuating magnetic fields in a reversed field pinch (invited)

Brower

Ding

Terry

et al. 2003

Review of Scientific Instruments

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Articles you may be interested inFar-infrared polarimetry diagnostic for measurement of internal magnetic field dynamics and fluctuations in the C-MOD Tokamak (invited)a) Rev. Sci. Instrum. 83, 10E316 (2012); 10.1063/1.4731757 Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pincha) Rev. Sci. Instrum. 83, 10E302 (2012); 10.1063/1.4728098 Electron thermal transport within magnetic islands in the reversed-field pincha) Phys. Plasmas 17, 056115 (2010); 10.1063/1.3388374 Measurement of electron transport in the Madison Symmetric Torus reversed-field pinch (invited) Rev. Sci. Instrum. 72, 1039 (2001); 10.1063/1.1319613First results from the far-infrared polarimeter system on the Madison Symmetric Torus reversed field pinch Rev.New developments in Faraday rotation polarimetry have provided the first measurements of current density profile and core magnetic fluctuations in the core of a high-temperature reversed field pinch. This has been achieved by a fast-polarimeter system with time response up to 1 s and phase resolution Ͻ1 mrad. Recent experiments on Madison Symmetric Torus have directly measured radial magnetic field fluctuations in the plasma interior with amplitude 33 G, ϳ1%. A broad spectrum of magnetic fluctuations is observed up to 100 kHz. Relaxation of the current density profile at the sawtooth crash occurs on the timescale of 100 s. Reversed-field pinch behavior is determined in large part by magnetic fluctuations driven by the radial gradient in the parallel current density. Hence, measurement of magnetic fluctuations and the current density profile is essential to understand the link between the current density profile, fluctuations, and transport.

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Section: Introductionmentioning

confidence: 99%

Laser polarimetric measurement of equilibrium and fluctuating magnetic fields in a reversed field pinch (invited)

Brower

Ding

Terry

et al. 2003

Review of Scientific Instruments

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“…Millimeter ͑mm͒ wave interferometry 1,2 techniques along with polarimetry 3,4 and optical emission diagnostics 5,6 have been widely used as nonperturbing methods for plasma diagnostics. Faraday rotation-based polarimetry originally developed for magnetic field measurement can be used as an accurate densitometer for magnetized plasmas.…”

Section: Introductionmentioning

confidence: 99%

Plasma interferometry at high pressures

Akhtar

Scharer

Tysk

et al. 2003

Review of Scientific Instruments

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A general formulation for the measurement of plasma density and effective collision frequency for lowly as well as highly, collisional plasmas using millimeter wave interferometry is presented. In the presence of high density and collisionality at high gas pressures where the collision frequency ͑͒ is of the order of both the plasma ( p ) and the wave frequency of the millimeter wave ͑͒ ( ϳ, p ), the measured line-average plasma density has a complex dependence on phase shift as well as the amplitude change of the millimeter wave signal. The measurement scheme and analysis presented in this article show that for collisional plasmas, simultaneous measurement of the phase change and the amplitude change data is required to uniquely determine the plasma density and collision frequency. The treatment allows the application of millimeter wave interferometry to a wide range of relative collision frequency, wave frequency and plasma frequency since it uniquely determines the line-average plasma density and effective collision frequency using the phase and amplitude change data. This diagnostic is particularly valuable at plasma densities (n e Ͻ10 14 /cm 3 ) and high pressures ( PϾ10 Torr) where Langmuir probe and optical emission diagnostics including the Stark effect are not accurate for density measurements.

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“…Polarimeters are used to measure the birefringence of materials, which provide various kinds of information such as sugar content, mechanical stress distribution or rock provenance. Polarimeters are also important diagnostics in magnetic confinement fusion experiments to measure electron density [1] and magnetic fields [2]. They measure Faraday rotation that is a rotation of the polarization plane of light (or electromagnetic wave) caused by the circular birefringence of plasma attributable to electron density and magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

“…Polarimeters have been widely used in fusion experiments: (Tokamak-type devices) TEXTOR [3], JT-60 [4], JET [5], TFTR [6], DIII-D [7], ToreSupra [8], C-Mod [9], NSTX [10], EAST [11], J-TEXT [12], ASDEX-U [13], (Stellarator-type devices) LHD [1], W7-AS [14], CHS [15], H-1 [16], and (Reversed-Field-Pinch-type devices) MST [17], RFX [18], RTP [19]. Probing laser beams pass author's e-mail: imazawa.ryota@qst.go.jp through plasma, and polarimeters measure the change of the polarization state of the laser light owing to the Faraday effect (i.e.…”

Section: Introductionmentioning

confidence: 99%

Measuring Faraday Effect in Z-Cut Crystal Quartz at Wavelength of 118.8 µm for Polarimeter

Imazawa

Nakayama

Akiyama

2018

Plasma and Fusion Research

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Faraday rotation angle in Z-cut crystal quartz at a wavelength of 118.8 µm was measured for the first time. Z-cut crystal quartz is used in vacuum windows of polarimeters for plasma diagnostics that use far-infrared light. ITER poloidal polarimeter uses double vacuum windows of 10-mm Z-cut crystal quartz discs in compliance with nuclear safety. According to the Becquerel model, thick Z-cut crystal quartz may lead to non-negligible Faraday rotation that must be compensated for to measure the pure polarization change attributable to the plasma. For the first time, this paper measures Faraday rotation at the wavelength of 118.8 µm by means of the rotating linear polarizer method. The Becquerel model is not applicable at the wavelength of 118.8 µm and Faraday rotation resulting from the Z-cut quartz vacuum window is negligible even with a magnetic field of 0.3 T and a 10-mm thick vacuum window.

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Faraday rotation densitometry for Large Helical Device

Cited by 15 publications

References 5 publications

Laser polarimetric measurement of equilibrium and fluctuating magnetic fields in a reversed field pinch (invited)

Laser polarimetric measurement of equilibrium and fluctuating magnetic fields in a reversed field pinch (invited)

Plasma interferometry at high pressures

Measuring Faraday Effect in Z-Cut Crystal Quartz at Wavelength of 118.8 µm for Polarimeter

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