Untitled

et al. 2008

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A short wavelength far infrared laser whose wavelength is about 50 m is preferable for a polarimeter and an interferometer for high density operations in the Large Helical Device ͑LHD͒ and on future large fusion devices such as ITER. This is because the beam bending effect ͑ϰ 2 ͒ in a plasma, which causes fringe jump errors, is small and the Faraday and the Cotton-Mouton effects are moderate. We have developed a polarimeter with highly resistive silicon photoelastic modulators ͑PEMs͒ for the CH 3 OD laser ͑ = 57.2 and 47.7 m͒. We performed bench tests of the polarimeter with a dual PEM and demonstrated the feasibility for the polarimeter. Good linearity between actual and evaluated polarization angles is achieved with an angular resolution of 0.05°and a temporal resolution of 1 ms. The baseline drift of the polarization angle is about 0.1°for 1000 s.

Section: B Optical Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Short wavelength far infrared laser polarimeter with silicon photoelastic modulators

Akiyama

et al. 2008

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“…Among these oscillation lines the most powerful line was found to be a 57.2 m CH 3 OD laser line 5 which was able to oscillate simultaneously at 47.6 m every 5 ϫ 57.2 m ͑ϳ6 ϫ 47.6 m͒ by tuning the FIR laser cavity length. 6 Figure 2(a) shows a Fabry-Pérot (FB) interferometer which is used to measure the wavelength of the laser oscillation line. By rotating the polarizer vertically or horizontally, one oscillating line is selected to feed to the Fabry-Pérot interferometer.…”

Section: New Two Color Fir Laser Interferometermentioning

confidence: 99%

Development of a new two color far infrared laser interferometer for future fusion devices

Tokuzawa

et al. 2004

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A new two color far infrared (FIR) laser interferometer under development for future fusion devices will be presented. The laser wavelength is optimized from the consideration of the beam refraction effect due to plasma density gradient and signal-to-noise ratio for an expected phase shift due to plasmas. Laser lines of 57.2 and 47.6 m are found to be suitable for the applications to high performance plasmas of Large Helical Device and future fusion devices such as the International Thermonuclear Experimental Reactor. The output power of 57.2 m CH 3 OD laser is estimated to be ϳ1.6 W, which is the highest laser power in the FIR wavelength regime. The optical configuration of a new interferometer system using two colors will be proposed. In the system, one detector simultaneously detects the beat signals of the 57.2 and 47.6 m laser lines, and each interference signal can be separated electronically (1 MHz for 57.2 m and 0.84 MHz expected for 47.6 m). Mechanical vibration can be compensated by using the two color interferometer. The present status of the development of the system is also presented.

“…In the International Thermonuclear Fusion Experimental Reactor ͑ITER͒, a poloidal polarimeter based on the Faraday effect of a far-infrared laser beam passing though the plasma has been designed 1 to measure the profile. A 118.8 m CH 3 OH laser line is proposed as a probing light source for the polarimeter, since the CH 3 OH laser line is the shortest and high power far-infrared laser oscillation line among many oscillation lines applied on fusion devices so far. The Faraday rotation angles that can be expected in ITER are large enough to be measured accurately.…”

Section: Introductionmentioning

confidence: 99%

Development of two color laser diagnostics for the ITER poloidal polarimeter

Akiyama

et al. 2010

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Two color laser diagnostics using terahertz 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 and 47.7 m by using a twin optically pumped CH 3 OD laser, and confirmed the original function, compensation of mechanical vibration, of the two color laser interferometer. In this article, application of the two color laser diagnostics to the ITER poloidal polarimeter and recent hardware developments will be described.