The Jon Beam Opening Switch

Plasma opening switches (POS\´s) have shown excellent characteristics in pulsed power applications. Proposed POS scaling predicts that the fastest opening time for a given conducted current should occur using a high-velocity low-density plasma as the switch medium. The ion beam opening switch (IBOS) uses a charge-neutral ion beam of 100-300 kV, ¿ 120 A/cm2 as the switch "plasma." Its velocity of up to 600 cm/¿s and density of ~1012/cm3 make this a very fast low-density plasma compared with typical 10 cm/¿s and 1013/cm3 POS plasmas. The IBOS has conducted ¿ 70 kA flowing in a parallel-plate transmission line driven by a 4-¿ pulser. IBOS opening time is load dependent, being ¿ 4 ns into a 15-nH load and about twice as long into a 4-¿ electron diode load. However, switch impedance is not zero during the entire conduction time, rising to ¿ 3 ¿ by the time of peak current. Peak current conducted before opening does not vary linearly with either injected ion current or switch axial length. Instead, the conduction current scales with plasma density in the switch, and is nearly independent of switch area until the area is restricted to a narrow (~1 cm) strip.