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Generation of high pulsed magnetic field using a low inductance surface switch

Auvray, , Larour, J., Moustaizis Stavros

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Summary

In experimental physics, a number of domains need the intense magnetization of a rather large volume, namely in condensed matter science. In laser-matter interaction and plasma science, the magnetic field may extend the interaction time of the charged particles. But the B-field values of interest, as predicted by analytical study or by numerical simulation, commonly overtake the 50-60T range, a limit for a reasonable capital investment. Moreover, the existing materials cannot withstand fields of 100T or more and some experiments are conducted in a semi-destructive mode, i.e. the coils explode radially, preserving the cell and the diagnostics. The single turn coil (STC) is an option for reaching such fields in a non-destructive pulsed mode. In order to study the generation of high energy particles for neutron production, we have have estimated that convenient operating conditions are a peak value of 50T in few cm3. Translated in current intensity, this objective is close to IMA with a rising time of 1 ?s. To get such a very high current, we have built a low impedance transmission line connected to a massive brass STC with a 10 to 16mm bore. Two types of capacitor banks were used, based on 4.2-?F 50-kV low-inductance Haefely caps, charged under 30kV. The key component in the flat transmission line is a surface switch which has been described previously and can have an insertion inductance as low as few nH. In this switch, a number of channels are triggered along a melamina surface by an underlying conducting comb. Under the present conditions, when the channel number is 15 or more, a significant reduction of the inductance is observed (typ. 13 to 16nH for the whole circuit) and the peak current can reach 850kA, corresponding to 26 to 30T on axis. The field mapping, recorded with a mm axial resolution, is coherent with STC calculation. The paper will describe in detail the experimental setup, the associated probes, the calibration procedure and the results.- We will conclude by presenting an alternative switch, currently under construction, able to increase the peak current, the reproducibility of B and the device lifetime.

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