A new high repetition rate Nd:YAG Thomson Scattering system is developed for the Heliotron J helical device. A main purpose of installing the new system is a temporal evolution measurement of a plasma profile for an improved confinement physics such as the edge transport barrier (H-mode) or the internal transport barrier of the helical plasma. The system has 25 spatial points with ∼ 10mm resolution. Two high repetition Nd:YAG lasers (> 550mJ@50Hz) realize the measurement of the time evolution of the plasma profile with ∼ 10ms time intervals. Scattered light is collected with a large concave mirror (D = 800mm, f /2.25) with a solid angle of ∼ 100mstr and transferred to interference filter polychromators by optical fiber bundles in a staircase form. The signal is amplified by newly designed fast preamplifiers with the DC and AC output which reduces the low frequency background noise. The signals are digitized with the Multi-event QDC, fast gated integrators. The data acquisition is performed by the VME-based system which is operated by the CINOS.
A new laser timing controller for the high time-resolution Nd:YAG Thomson scattering system with two Nd:YAG lasers has been developed to study improved confinement physics in Heliotron J. A PIC-based timing controller synchronizes the timings of laser oscillations with plasma discharges and enables the measurement of plasma profiles with a precision of <1 μs. The timing controller is used for the "soft start" of the system, which protects the optical components against initial unstable laser oscillations. The timing controller is designed to precisely control the delay time of the laser pulse from one laser to another, and to investigate the profile change of electron temperature and density within a short time span (> 80 ns), which is crucial for transport physics studies including spontaneous transitions.
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