Fuse conditioning of the output of a capacitor bank to drive a PEOS

Abstract

The paper details capacitor bank experiments performed to assess the performance of a plasma erosion opening switch (PEOS). A description is given of the PEOS, which was of an inexpensive and expendable design, and was intended for use as the final stage of a flux compressor output conditioning circuit. Techniques usicg automatically operating exploding foils, as both opening and closing switches, condition the 9ps quarter-wave output pulse from the capacitor bank to a 400ns pulse to the PEOS. An outline is given of the computer modelling and the experimental procedures used to establish the optimum operating conditions, and results are presented which illustrate the behaviour of the PEOS.

Global problems and energy

“…It is relatively straightforward to adapt the system for use with the output of a high energy flux compression generator, typically with a current rise time of about 20 µs. Load voltages increasing at up to 1 MV ns −1 can be expected for such a system working into a highly resistive load [2,4].…”

“…Opening switch (OS) Closing switch (CS) Load Figure 1 shows the equivalent electrical arrangement of the two-stage conditioning circuit, with the energy source being the capacitor bank (C) used in previous studies [3,4]. The main switch (S 1 ) and the closing and opening switches (CS and OS) were also described in those publications.…”

“…They were solved algebraically for dI/dt, with the resulting set of first-order differential equations then being solved numerically [3] using FORTRAN software. At each time step of the solution the OS foil resistance R f and the CS bridge resistance R b were obtained using experimentally derived variations of the dynamic resistance ratio with specific deposited energy for the 17 µm copper foil [3] and the 100 µm aluminium bridges [4], after first calculating the specific energy deposited. The second stage of the conditioning circuit (including the PEOS) was coupled according to a closing-switch delay function [4].…”

“…At each time step of the solution the OS foil resistance R f and the CS bridge resistance R b were obtained using experimentally derived variations of the dynamic resistance ratio with specific deposited energy for the 17 µm copper foil [3] and the 100 µm aluminium bridges [4], after first calculating the specific energy deposited. The second stage of the conditioning circuit (including the PEOS) was coupled according to a closing-switch delay function [4]. Calculation of the PEOS resistance was by the standard NRL method [9], using as input the following data for the PEOS plasma: (i) carbon plasma characteristics [7] in accordance with the time delay between the flashboard action and the start of the PEOS input current ( t ≈ 1 µs), type of ion: C ++ , density 1.35 × 10 19 m −3 and velocity 9 × 10 4 m s −1 ;…”

“…A complete conditioning circuit for an FCG will therefore consist of a stage (or stages) of current sharpening to reduce the initial FCG current rise time to some hundreds of nanoseconds, followed by a PEOS. Details of the circuit components used in a current research programme at Loughborough have been presented previously, as have computer models used in predicting the performance of the system [1,3,4].…”