High voltage pulse of short duration to feed solenoids for intense ion bean transport

Abstract

A high voltage pulser up to 50 kV, with a main pulse of 2$mu$s time duration, was realized using a fast high voltage capacitor of 150 nF (50 kV) connected to the ground by a homemade spark-gap. The circuit, contained in a metallic box, had short electric connections in order to reduce any stray inductances. The diagnostics was performed by two systems: an auto-integrating Rogowski coil and an integrator connected to a current transformer, both suitable for pulses longer than 1$mu$s. In order to get the above characteristic the Rogowski coil circuit must have a ratio L/R higher than 1$mu$s, while the integrator, formed by a resistance and a capacitance, must get the product RC higher than 1$mu$. In the first system, the load resistance can be easily reduced, instead it is very difficult to reduce the coil resistance. The Rogowski coil we build exhibited a ratio L/R=2 $mu$s, while the integrator circuit connected to the transformer exhibited a value RC=5$mu$s . We made a solenoid with an inductance of 2.8 $mu$H (11 rings, length 14 cm) which was fed by the current generated by the pulser up to 4 kA, 1$mu$s at 24 kV of charging voltage. Under the above conditions, we estimate a magnetic field of 0.4 T applying the Ampere law. Actually, the magnetic field was measured in dc mode by means of a Hirst GM07 gauss-meter having a conversion coefficient of 0.08 mT/A which determined a magnetic field at the center of 320 mT. Potentially, at the maximum voltage of 50 kV we can get a magnetic field up to of 0.7 T.