Behavior of ablated plasma in laser-triggered vacuum switch

Bi-directional pulse generator system is well convenient to generate a high-current charged particle beam using a linear induction accelerator because it requires no induction magnetic cores. However, in order to obtain an ideal bi-directional voltage pulse, it is necessary to reduce the inductance and resistance of the main gap switch. Therefore, laser-triggered vacuum switch is adequate for a main switch of bi-directional pulse generator because of its low inductance, high speed switching and easy parallel operation. In previous study, the electrical characteristics of a laser-triggered multi-arc vacuum switch were investigated. It is observed that a laser-triggered vacuum gap switch can be operate with very low delay time and very low jitter in wide range of applied voltage as long as negative voltage is applied to the target electrode. In present study, the behavior of ablated plasma in the gap was investigated. The switch electrodes were made of copper or aluminum, the surfaces of which were irradiated through lenses by the fundamental (1064 nm) or the third harmonics (355 nm) of Q-switched Nd:YAG laser. The maximum output energy and the pulse width of the laser are 650 mJ and 4-7 ns, respectively. The influences of the target materials, the wavelength and the output energy of the laser beam were discussed.