Influence of transverse magnetic field on plume dynamics and optical emission of nanosecond laser produced tungsten plasma in vacuum

The particles transport and optical emission of tungsten plasma in magnetic field are two of the prime aspects for the diagnosis of plasma wall interaction process in nuclear devices such as EAST tokamak. In this work, the effect of the magnetic field (1.1 T) on the laser produced tungsten plasma plume dynamics and its optical emission produced by laser in vacuum (similar to 4 x 10(-3) Pa) were investigated. Fast imaging results presented that magnetic field confined the plasma and affected the plasma geometry. Temporal evolution of the optical emission showed that the continuum radiation at early stage (> 100 ns) was not affected by the magnetic field while the tungsten ionic and atomic lines were significantly enhanced at later delay times (> 200 ns,> 400 ns, respectively). The negligible influence on the early continuum radiation was due to the laser-plasma pressure was far higher than the magnetic pressure as the plasma was hot and dense at early times. The higher electron temperature (T-e) and electron density (n(e)) at later delay times were also observed in the magnetic field. The time-dependent plume dynamics in the magnetic field was correlated to the temporal variation of the plasma parameter beta (the ratio of plasma pressure to magnetic pressure) and the electron collision frequency (v(e)), and electron cyclotron frequency (omega(ce)) were also discussed. Moreover, the information including plasma evolution, plasma velocity, electron temperature electron density, ionic and atomic velocities with and without magnetic field were obtained.