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

Abstract

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.

Design study of a combined interferometer and polarimeter for a high-field, compact tokamak

“…Some efforts have been devoted to the development of a twocolor interferometer-polarimeter based on CH 3 OD laser sources with k ¼ 57:2 lm and 47:7 lm. 35,36 At present, however, this technology is immature compared to CO 2 lasers, whose reliability and robustness constitute a decisive advantage.…”

Stabilization of 48- and 57-μ m CH3OD lasers for plasma diagnostics

“…In addition, simultaneously oscillated two-color FIR lasers are necessary for the compensation of the mechanical vibration, because the probe wavelength is shortened. Therefore, we have developed a two-color interferometer and polarimeter using 48-µm (6.3 THz) and 57-µm (5.2 THz) CH 3 OD lasers pumped by a 9R(8) CO 2 laser [3]. The pump CO 2 laser wavelength is 9.342 µm (32.1 THz).…”