2.C Fast, Optically Triggered, Superconducting Opening Switches

In high-power applications, opening switches play an important role. These switches are required to carry high currents (100 A-10 MA) and operate with short switching times ( l0ms-Ions). Moreover, before opening, the switch must conduct current to a parallel circuit branch (load) and withstand the voltage across the load. If there is no load in parallel to the switch, it must absorb all the energy stored in the circuit inductance. For a practical pulsed-power generator employing inductive energy storage, the opening switch has to be operated repeatedly.These diverse requirements make the design of an opening switch a challenging problem. I Theexisting opening switches include plasmaopening switch (POS), plasma erosion opening switch (PEOS), plasma flow switch (PFS), reflex opening switch(ROS), and explosive opening switch (EOS). All these switches are used to interrupt the flow of current in the circuit. An alternative approach to the switching problems is the superconducting, inductively coupled switch (SICS), in which the load is connected to the secondary coil of the transformer while current flows through the primary. Thecurrent flow in the primary is uninterrupted. The switching is accomplished by removing a magnetic screen that isolates the secondary from the primary. This approach is particularly suited to superconducting magnetic-energy storage (SMES) applications where apersistent current is required. Since there is no switch in the storage coil (primary), there is no dissipation of energy. The number of times switches like PEOS can be operated is limited because the surface discharge degrades the source. Explosive switches are also not suitedfor applications requiring repetitive switch operation. The SICS has been operated up to kHz repetition rates using a train of short laser pulses, and no degradation of performance has been observed.