Advanced Laser Diagnostics for Electron Density Measurements

Kawahata, K.; Akiyama, Tsuyoshi; Pavlichenko, R.; Tanaka, K.; Ito, Y.; Nakayama, Keiichi I.; Okajima, S.; Tsuji‐Iio, S.

doi:10.1585/pfr.2.s1027

Cited by 3 publications

(2 citation statements)

References 15 publications

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“…The measurement system for plasma electron density, the poloidal magnetic field and the current density profile is an important part of magnetically confined fusion plasma diagnostics. Far-infrared (FIR) laser heterodyne interferometers have been regarded as an effective diagnostic tool to measure the plasma electron density in many fusion devices [1,2], such as JET [3] and LHD [4]. Since the 2006 experimental campaign, a hydrogen cyanide laser interferometer has been used at the HL-2A tokamak [5].…”

Section: Introductionmentioning

confidence: 99%

A precision control method for plasma electron density and Faraday rotation angle measurement on HL-2A

Zhang

Ding

et al. 2017

Plasma Sci. Technol.

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The precision of plasma electron density and Faraday rotation angle measurement is a key indicator for far-infrared laser interferometer/polarimeter plasma diagnosis. To improve the precision, a new multi-channel high signal-to-noise ratio HCOOH interferometer/polarimeter has been developed on the HL-2A tokamak. It has a higher level requirement for phase demodulation precision. This paper introduces an improved real-time fast Fourier transform algorithm based on the field programmable gate array, which significantly improves the precision. We also apply a real-time error monitoring module (REMM) and a stable error inhibiting module (SEIM) for precision control to deal with the weak signal. We test the interferometer/polarimeter system with this improved precision control method in plasma discharge experiments and simulation experiments. The experimental results confirm that the plasma electron density precision is better than 1/3600 fringe and the Faraday rotation angle measurement precision is better than 1/900 fringe, while the temporal resolution is 80 ns. This performance can fully meet the requirements of HL-2A.

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Section: Introductionmentioning

confidence: 99%

A precision control method for plasma electron density and Faraday rotation angle measurement on HL-2A

Zhang

Ding

et al. 2017

Plasma Sci. Technol.

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“…Figure 1 shows a schematic drawing of the two color laser interferometer [5,6] combined with a polarimeter. The system consists of a twin terahertz laser which simultaneously oscillates at 57.2 µm and 47.7 µm, beam splitters (BS), beam combiners (BC), and phase/rotation detection systems.…”

Section: Introductionmentioning

confidence: 99%

Progress in development of two color laser diagnostics for the ITER poloidal polarimeter

Kawahata¹,

Akiyama²,

Tanaka³

et al. 2012

J. Inst.

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Two color laser diagnostics using THz laser sources are under development for a high performance operation of the Large Helical Device and for future fusion devices such as ITER. So far, we have achieved high power laser oscillation lines simultaneously oscillating at 57.2 µm (1.6 W) and 47.7 µm (0.8 W) by using a twin optically-pumped CH 3 OD laser. And, we confirmed the usefulness of this two color laser operation for two-color laser interferometry in a test stand. For the measurement of the Faraday rotation angle we have developed a photo-elastic modulator (PEM) operating around 50 µm, and performed bench tests of the polarimeter with dual PEMs and demonstrated the feasibility of the polarimeter. The achieved angular resolution is 0.01 degrees with a time resolution of 1 ms, which satisfies diagnostic requirements for q-profile measurements on ITER (0.05 deg. at 10 ms time resolution). In this symposium, recent hardware developments and simultaneous measurements of a phase shift and a rotation angle will be presented.

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Recent Progress of the HL-2A Multi-Channel HCOOH Laser Interferometer/Polarimeter

Zhang

Zhongchao

et al. 2015

Plasma Sci. Technol.

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A multichannel methanoic acid (HCOOH, λ = 432.5 µm) laser interferometer/polarimeter is being developed from the previous eight-channel hydrogen cyanide (HCN, λ=337 µm) laser interferometer in the HL-2A tokamak. A conventional Michelson-type interometer is used for the electron density measurement, and a Dodel-Kunz-type polarimeter is used for the Faraday rotation effect measurement, respectively. Each HCOOH laser can produce a linearly polarized radiation at a power lever of ∼30 mW, and a power stability <10% in 50 min. A beam waist (diameter d0 ≈12.0 mm, about 200 mm away from the outlet) is finally determined through a chopping modulation technique. The latest optical layout of the interferometer/polarimeter has been finished, and the hardware data processing system based on the fast Fourier transform phasecomparator technique is being explored. In order to demonstrate the feasibility of the diagnostic scheme, two associated bench simulation experiments were carried out in the laboratory, in which the plasma was simulated by a piece of polytetrafluoroethene plate, and the Faraday rotation effect was simulated by a rotating half-wave plate. Simulation results agreed well with the initial experimental conditions. At present, the HCOOH laser interferometer/polarimeter system is being assembled on HL-2A, and is planned to be applied in the 2014-2015 experimental campaign.

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Advanced Laser Diagnostics for Electron Density Measurements

Cited by 3 publications

References 15 publications

A precision control method for plasma electron density and Faraday rotation angle measurement on HL-2A

A precision control method for plasma electron density and Faraday rotation angle measurement on HL-2A

Progress in development of two color laser diagnostics for the ITER poloidal polarimeter

Recent Progress of the HL-2A Multi-Channel HCOOH Laser Interferometer/Polarimeter

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