Nd:YAG laser Thomson scattering diagnostics for a laboratory magnetosphere.

A new Nd:YAG laser Thomson scattering (TS) system has been developed to explore the mechanism of high-beta plasma formation in the RT-1 device. The TS system is designed to measure electron temperatures (T) from 10 eV to 50 keV and electron densities (n) of more than 1.0 × 10 m. To measure at the low-density limit, the receiving optics views the long scattering length (60 mm) using a bright optical system with both a large collection window (260-mm diameter) and large collection lenses (300-mm diameter, a solid angle of ∼68 × 10 str). The scattered light of the 1.2-J Nd:YAG laser (repetition frequency: 10 Hz) is detected with a scattering angle of 90° and is transferred via a set of lenses and an optical fiber bundle to a polychromator. After Raman scattering measurement for the optical alignment and an absolute calibration, we successfully measured T = 72.2 eV and n = 0.43 × 10 m for the coil-supported case and T = 79.2 eV and n = 1.28 × 10 m for the coil-levitated case near the inner edge in the magnetospheric plasmas.