A scheme of a modular plasma-opening-switch-based generator of megaampere currents for experiments with Z-pinches

Abstract

A generator that is based on a plasma opening switch (POS) (Fig. 1a) contains a capacitive energy storage С 0 , a switch Sw (spark gap), an inductive stor age L 0 , a POS (two coaxial electrodes with a plasma jumper and a longitudinal magnetic field in the inter electrode gap), and an inductive load [1]. The induc tive storage L 0 includes the inductances of all elements of the capacitive storage-POS circuit, and the induc tive load L l includes the inductances of the POS-liner line, i.e., the inductances of the line L lin and liner L lnr .After the switch Sw is closed, the capacitive storage discharges through the plasma jumper of the POS to the inductive storage L 0 and the electric energy C 0 /2 transforms into the magnetic energy L 0 /2 (storage mode with the duration t st ≈ 1 μs). Under certain con ditions, the POS resistance abruptly increases and the current is switched to the load (current switching mode with the duration t sw ≈ 100 ns).Typical forms of oscillograms of the current in the inductive storage I 0 , current in the load I l , and voltage U pos across the POS are shown in Fig. 1b. As was shown in experiments in [2], an external magnetic field prevents a repeated POS closure and allows the voltage across the load to be held for ~1 μs.After the current switching, the liner supply circuit is inductive (Fig. 2a) with the current I l and the energy that can be supplied to the liner being W lnr = (L 0 + L lin + L lnr ) /2. In this case, the energy of an external (with 2 0 U 2 0 I I l 2 respect to the liner) circuit must be the main energy source, i.e., L 0 + L lin + L lnr ≥ 10 L lnr .( 1 )A typical oscillogram of the liner current I l that includes the current switching mode t sw and the liner compression mode t comp , when the stored energy is expended for the liner compression, is illustrated in Fig. 2b.Abstract-A modular scheme of a megaampere current pulse generator on the plasma opening switch (POS) basis with insulation of the POS interelectrode gap by a magnetic field created by an external source is pro posed for experiments with wire liners and other applications. The POS is fed from independent modules that are switched on in parallel. On the basis of an ИК 50 3 (50 kV, 3 μF) capacitor, a supply module with a cur rent through the equivalent part of the POS of up to 200 kA is designed and tested. The limiting POS param eters and the maximum permissible number of modules are determined, and circuit designs of the basic units of the generator are presented.