Z-pinch Discharge in Laser Produced Plasma

Z-pinch effects in a laser produced aluminium plasma were investigated with a relatively low current fast coaxial electrical discharge. The ion flux in the laser produced plasma (LPP) was monitored with a Langmuir ion probe and the line density was controlled by using an aperture to select the portion of the LPP which enters the discharge cell. The Zpinch dynamics were recorded using time-resolved imaging of the visible self-emission; the plasma was pinched to about one-third the initial radius. Both the laser and Z-pinch plasmas were diagnosed using timeand space-resolved spectroscopy; substantial heating was observed. The measured behaviour of the pinch was compared with the predictions of the slug model. INTRODUCTION Currently there is great interest in producing efficient, sources of extreme ultraviolet (EUV) radiation for lithography, Z-pinch plasmas have been shown to be intense emitters of EUV and x-ray radiation [1]. Z-pinch structures are created by driving a high electric current through a cylindrically symmetric plasma so that the Lorentz force compression of the plasma column produces the imploding structure. The portion of LPP under discharge in this experiment was selected and collimated through a 3 mm circular aperture in the cathode as seen in Fig. 1 (a). The value of the measured pinch radius was found in a good agreement with the value predicted by the slug model[2].. EXPERIMENTAL SETUP In this work a LPP under free expansion from a rotating aluminium target, as shown in Fig. 1 (a), approached a discharge cell where it was collimated by an aperture in the cathode of the cell. A 248 nm, 20 ns excimer laser pulse was focused on the target to a 1mm diameter spot, giving a laser fluence of 4 J cm -2 . The cathode was 1 cm from the target and the inter electrode gap was 1 cm. Two 5 mm x 10 mm windows were cut in the discharge cell to allow viewing the plasma along the axis orthogonal to the discharge axis. When the column of plasma contacts the anode it triggers the discharge. The coaxial discharge cell was connected to a low inductance DC circuit (L ≈ 60 nH) consisting of a 1.5 μF capacitor which was charged to a maximum of 1 kV. 37 EPS Conference on Plasma Physics D5.524