The use of any solid material as a fuel and the discharge stability make a laser triggered discharge-produced-plasma (LT-DPP) an attractive light source. Density, size, uniformity, and so on of a fuel control the pinch process by a Lorentz force, and understanding the plasma dynamics in the initial stage is the most important in the LT-DPP study. This work reports how a material for a pinch is supplied and how a laser-produced-plasma (LPP) generated on the electrode behaves before the main discharge current. Our study revealed that the material of a pinch plasma is mainly supplied by laser ablation of a cathode not by current heating of the electrodes. The delay time of a discharge is determined by the velocity of an LPP generated on the cathode, and the traveling velocity of about 1 × 105 m/s of LPP is determined by two factors: the pressure of LPP and acceleration by the electric field. Before the main discharge current starts to flow, two X-ray pulses are generated. The first X-ray pulse is generated on the cathode where a laser is irradiated. The second X-ray pulse is generated on the anode when the LPP generated on the cathode arrives, and the arrival of the LPP triggers the main discharge current. The material for the pinch is not the LPP, but supplied by laser ablation. A faintly bright region appears between electrodes several tens of ns after the start of the main discharge current and this region is slowly imploded and a pinch plasma is formed at the current peak.

In applying a laser-triggered discharge-produced plasma (LT-DPP) as a light source, the most important issues are the supply of fuel and the suppression of a large-scale nonuniformity called the zippering effect. This paper reports pinch formation in LT-DPP under various electrode separations from 4 mm to 10 mm, which provides information for suppressing the zippering effect. Spherically expanding fuel ablated from the cathode becomes visible when the discharge current becomes large. By 100 ns after the laser trigger, the laser-ablated fuel extends 5 mm from the cathode. The width of the fuel reduces gradually with the increase of the current and forms a pinch at the current peak at 200 ns for the case of a 5mm electrode separation. When the electrode separation is larger, neck-like fuel distribution is observed and the pinched portion propagates toward the anode. The condition for reducing the zippering effect is discussed.

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