LASER-ABLATION-ASSISTED-PLASMA DISCHARGES OF ALUMINUM IN A TRANSVERSE-MAGNETIC FIELD

Laser-ablation-assisted-plasma discharges (LAAPD) have been used to en hance the ionization of laser ablated aluminum metal. Ablation is acco mplished by focusing a KrF excimer laser (248 nm, 40 ns, less-than-or- equal-to 0.4 J) on a solid aluminum target with a fluence of 4 J/cm2. Peak plasma discharge voltage is 1-4 kV and peak plasma current is 0.2 -1 kA, while peak power is 0.1-1 MW. Gated emission spectroscopy is us ed to determine the charge states and the electronic temperatures with in the plasma discharge. With unmagnetized discharge parameters of 3 k V and 760 A, the observed light emission is dominated by transitions f rom Al2+ ions indicating nearly complete ionization of the plume. From the emission spectra intensities, an Al2+ electronic temperature of 3 .3 eV is determined. Emission spectra from unmagnetized LAAPD of 1.2 k V and 280 A show no visible Al2+ ion transitions indicating cooler pla sma and a lower ionization state. Introducing a 620 G transverse magne tic field (at 1.2 kV, 280 A) enhances the ionization due to the increa sed electron confinement and leads to the observance of the Al2+ lines as seen with discharges of 3 kV and 760 A.