Silicon-Controlled Rectifier Circuitry for Producing Pulsed Magnetic Fields

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Abstract
A switching circuit using a high powr silicon‐controlled rectifier to discharge a high energy (5 kJ), low voltage (450 V) capacitor bank into pulse coils immersed in liquid helium is described. A free‐wheeling diode assures that the pulses remain unidirectional. The circuit has successfully operated with inductance‐resistance‐capacitance (LRC) combinations yielding pulses having rise times τR and decay times τD in the ranges 0.80 msec ≤τR≤0.25 sec and 2.2 msec ≤τD≤1.2 sec, respectively. Another SCR is used to shunt unwanted capacitor energy to an auxiliary circuit at any desired time during the pulse duration. This function is used to protect the pulse coils from overheating and to conserve liquid helium. The use of special, fixed‐geometry copper coils is described which enables one to obtain initial rates of change of the applied magnetic field Ḣ0 which varied over many orders of magnitude (102<Ḣ08 Oe/sec). The circuit, while generally useful in most solid‐state studies requiring pulsed‐magnetic fields, was used to study flux‐jumping, rate effects, and critical currents in tubes and wires made of type II superconducting materials. Some of these experiments are described.

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