ヘリオトロン/トルサトロン装置SHATLET-Mへのレーザー生成プラズマの適用

An l=2, m=12 modular-coil heliotron/torsatron device, SHATLET-M, has been filled with plasmas produced by the irradiation of an intense pulsed CO2 laser beam on a tiny freefalling deutrium pellet. Plasma parameters, namely, line-integrated density, spatially averaged beta value, their decay constants, and plasma currents are measured. The size of the deutrium pellets is in typical cases 0.2mm in diameter and 1mm in length. The pellets are irradiated by a CO2 laser pulse with a total energy of about 300J and a pulse width of 1μs. Within 10 μs, a toroidal plasma is rapidly formed that has a small ititial toroidal plasma current with a peak value of less than 150A. This initial toroidal current is rapidly damped in about 20μs leaving a net-currentfree toroidal plasma for another 200-400 μs. The diamagnetic loop measurement shows that the initial peak value of spatially averaged beta which may contain non-thermal components ranges from 3 to 6%, where the average densety is about 1×1013cm-3. The density increases in proportion to B1.8±0.2 (B is the magnetic field strength.), and the maximum averaged beta increases about in proportion to B. The decay time constants of the averaged beta values are less than about 100μs and no disruptive instability has been observed within these periods.