Increased signal separation upgrade permits preliminary electron anisotropy measurements with Heliotron J multi-pass Thomson diagnostic.

A signal separation system is constructed on the multi-pass Thomson scattering system of Heliotron J to solve the problem of overlapping scattered light signals for the electron temperature anisotropy measurement. The phenomenon of overlapping scattered light signals is relieved by operating the signal separation system. A Raman scattering experiment is undertaken to verify the separation effect of the signal separation system. Two scattered light signals corresponding to two adjacent incidences of one laser shot were extended to 104 ns. Moreover, we applied the multi-pass Thomson scattering system with signal separation system to the electron temperature anisotropy measurement. No anisotropy was observed within the error bars in the initial experiment.

Design of a dual scattering angle multi-pass Thomson scattering system with signal separation function on Heliotron J.

This paper proposes a design of dual scattering angles multi-path Thomson scattering system with a signal separation function to solve the overlapping phenomenon of scattered light signals and to increase the measurement accuracy for the investigation of anisotropic electron velocity distribution. Furthermore, an optical path design is proposed to demonstrate how overlapping scattered light signals can be separated by setting the optical path in a limited room with a compact layout, which makes the incident interval between two overlapping scattered light signals 1.7 times longer than that of our current system. The specific position of each optical component existing in the system is determined via a Gaussian beam analysis to avoid damage caused by overexpansion of spot size with the application of two cooperating image relay systems. Conversely, a polychromator is optimized by resetting the pass waveband of the interference filter combination to achieve high accuracy in electron temperature (Te) measurement corresponding to two scattering angles simultaneously.

Spatially resolved measurement of helium atom emission line spectrum in scrape-off layer of Heliotron J by near-infrared Stokes spectropolarimetry.

For plasma spectroscopy, Stokes spectropolarimetry is used as a method to spatially invert the viewing-chord-integrated spectrum on the basis of the correspondence between the given magnetic field profile along the viewing chord and the Zeeman effect appearing on the spectrum. Its application to fusion-related toroidal plasmas is, however, limited owing to the low spatial resolution as a result of the difficulty in distinguishing between the Zeeman and Doppler effects. To resolve this issue, we increased the relative magnitude of the Zeeman effect by observing a near-infrared emission line on the basis of the greater wavelength dependence of the Zeeman effect than of the Doppler effect. By utilizing the increased Zeeman effect, we are able to invert the measured spectrum with a high spatial resolution by Monte Carlo particle transport simulation and by reproducing the measured spectra with the semiempirical adjustment of the recycling condition at the first walls. The inversion result revealed that when the momentum exchange collisions of atoms are negligible, the velocity distribution of core-fueling atoms is mainly determined by the initial distribution at the time of recycling. The inversion result was compared with that obtained using a two-point emission model used in previous studies. The latter approximately reflects the parameters of atoms near the emissivity peak.