I. Sakuma

Vapor shielding effects on energy transfer from plasma-gun generated ELM-like transient loads to material surfaces

Energy transfer processes from ELM-like pulsed helium (He) plasmas with a pulse duration of ~0.1 ms to aluminum (Al) and tungsten (W) surfaces were experimentally investigated by the use of a magnetized coaxial plasma gun device. The surface absorbed energy density of the He pulsed plasma on the W surface measured with a calorimeter was ~0.44 MJ m−2, whereas it was ~0.15 MJ m−2 on the Al surface. A vapor layer in front of the Al surface exposed to the He pulsed plasma was clearly identified by Al neutral emission line (Al i) measured with a high time resolution spectrometer, and fast imaging with a high-speed visible camera filtered around the Al i emission line. On the other hand, no clear evaporation in front of the W surface exposed to the He pulsed plasma was observed in the present condition. Discussions on the reduction in the surface absorbed energy density on the Al surface are provided by considering the latent heat of vaporization and radiation cooling due to the Al vapor cloud.

Characterization of Gun Plasma Penetrated Into a Steady State Plasma Device

Characterization of a pulsed plasma formed with a plasma gun device was performed. The averaged electron density was measured with an interferometer system using a Zeeman laser at 633 nm. It was found that the plasma with the density of ~ 1022 m-3 was successfully formed. The temporal evolution of the plasma was observed with a fast framing camera. It was found that the shape of the plasma was significantly varied temporally. From the intensity profile, the vertical emission profile was obtained using Abel inversion. The emission profile had a flat top shape with the radius of ~ 20 mm, and gradually decreased with the radius. The penetration behavior of the gun plasma across the magnetic field was observed.

Development of a magnetized coaxial plasma gun for simulation experiment of type-I ELM heat loads

The magnetized coaxial plasma gun (MCPG) device at University of Hyogo for simulation experiments of type-I ELM heat loads has been upgraded to improve the performance. The characteristics of the upgraded MCPG device have been investigated and compared with the previous one. The capacitor bank energy for the power supply of the MCPG was increased from 24.5 kJ to 144 kJ. In the preliminary experiments, the plasmoid with duration of ∼0.6 ms, the incident ion energy of ∼40 eV, and the surface absorbed energy density of ∼2 MJ/m2 was successfully produced by the present MCPG device at the gun voltage of 6 kV.