Measurement of type-I ELM pulse propagation in SOL through BES use of MSE diagnostics in JT-60U and impact of ELM on MSE diagnostics

Suzuki, Takahiro; Oyama, Naoyuki; Asakura, Nobuyuki; Fujita, Takaaki

Since transient heat and particle loads by the type-I ELMs are significantly high for the plasma facing components of the fusion reactor, understanding propagation of plasma ejected by ELMs (ELM pulse) in SOL is important. Increase in the SOL plasma density due to the ELM pulse has been measured through the increase in beam emission (BE) at various radial locations in SOL near equatorial plane, using MSE diagnostics as beam emission spectroscopy (BES) diagnostics. From the temporal delay of the increase of BE as a function of major radius in the SOL, radial velocity of the ELM pulse propagation has been evaluated as 0.8-1.8 km/s. In accurately evaluating the velocity, elimination of background (BG) light from the BES signal is found essential since the delay of the net BE is veiled by the BG light that increases in synchronous to the ELM pulse. The intermittent increase in the BG light synchronized with ELMs has been observed in MSE channels viewing not only the SOL but also the main plasma. Since this BG light affects the magnetic pitch angle measurement by MSE diagnostics as was reported in JET, the impact of the intermittent BG light by ELMs on MSE diagnostics has been investigated numerically. When intermittent BG light by ELMs mixes with PEM modulation for MSE diagnostics, broadband spectrum of the impulse-like BG light disturbs the spectrum intensities, even if the BG light is not polarized. Numerical simulation shows that error induced by ELMs piles up if ELM frequency is higher than , where is time constant of lock-in amplifier detecting PEM modulation, and then, the error remains even between ELMs.