Effect of transverse magnetic field on dynamics of Sn plasma produced by CO₂ Laser

Full text: In the present work we report the effect of magnetic field on the emission intensity of the neutral and singly ionized transition line, spatial and temporal variation in the plasma properties of the tin plasma in vacuum produced by the CO₂ laser. The plasma electron temperature is inferred by the Boltzmann plot method from singly ionized Sn emission lines, and plasma electron density is inferred using Stark broadened profiles. In the temporal variations, the temperature with and without magnetic field of 0.64T is estimated as (1.48-0.63) eV and (1.04- 0.58) eV at the delay of (200 – 1100) ns. Another experiment the electron temperature is measured in the range of (0.53 - 1.28) eV, and electron density is measured in the range of (9.19×1015 - 7.45×1016) cm-3, as the laser intensity is varied from (1×1010 to 2.5×1010) W/cm². The plasma shielding effect has been observed within the laser intensities of (2×1010 – 2.5×1010) W/cm². In order to get more information regarding the time taken by a particular state of the constituent to evolve after the onset of plasma, TOF emission studies were made for tin with and without magnetic field. This technique gives details on the velocity and K.E of the emitted particles. TOF profiles were taken at different distances from the target surface with and without magnetic field, in order to study the effect magnetic field. Time resolved studies were made for Sn II (556.19 nm) and Sn I (317.5 nm) species at a distance of 0mm, 1mm, 2mm and 3mm from the target surface in the presence and absence of the magnetic field. The expansion velocities of the Sn II were found to be greater than the excited neutrals. The expansion velocities of Sn II at 556.19 nm for 1mm distance from the surface with and without magnetic field were found to be 0.19×106 cm/sec and 0.23×106 cm/sec respectively. Similarly, expansion velocities of Sn II at 556.19 nm for 3mm distance from the surface with and without magnetic field were found to be 0.27×106 cm/sec and 0.32×106 cm/sec respectively. The observed deceleration of neutrals and ions compared to the field free case is consistent with magnetohydrodynamics model in which K.E of expansion is converted into joule heating. We explain the results by considering the role of various atomic processes viz. electron impact excitation and recombination. (author)