In situ determination of the static inductance and resistance of a plasma focus capacitor bank

Abstract

The static (unloaded) electrical parameters of a capacitor bank are of utmost importance for the purpose of modeling the system as a whole when the capacitor bank is discharged into its dynamic electromagnetic load. Using a physical short circuit across the electromagnetic load is usually technically difficult and is unnecessary. The discharge can be operated at the highest pressure permissible in order to minimize current sheet motion, thus simulating zero dynamic load, to enable bank parameters, static inductance L(0), and resistance r(0) to be obtained using lightly damped sinusoid equations given the bank capacitance C(0). However, for a plasma focus, even at the highest permissible pressure it is found that there is significant residual motion, so that the assumption of a zero dynamic load introduces unacceptable errors into the determination of the circuit parameters. To overcome this problem, the Lee model code is used to fit the computed current trace to the measured current waveform. Hence the dynamics is incorporated into the solution and the capacitor bank parameters are computed using the Lee model code, and more accurate static bank parameters are obtained.

Current Sheet Axial Dynamics of 2.5-kJ KSU-DPF Under High-Pressure Regime

“…The coupled-equations method allows for the motion and the current to be derived as the two solutions of the two equation system. The nature of the problem is such that the current waveform is a damped sinusoid with non-linear time-varying damping factor as well as frequency; these are correctly incorporated into the pointby-point solutions as the coupled equations are numerically solved [1,11]. Nevertheless the use of a damped sinusoidal current in the equation of motion may still be used as a simpler alternative for analytical purposes.…”

“…The current waveform was measured using Rogowski coil then analyzed using the RLC analysis [1]. The resulting values for the inductance and resistance incorporate contributions due to the motion of the current sheet.…”

“…The discharge current predominantly goes through diffusive ohmic regime rather than electromagnetic regime. Although the high pressure gas greatly slows down the motion of the current sheet, a small displacement still exists, which adds an amount of inductance and resistance to the circuit; thus causing an over-estimation of the static parameters [1].…”

“…machine [1], [2].The plasma focus machines of Mather-type have been recently classified into two types according to the value of their static inductance [3]. The most reliable method to determine the DPF static parameters C o , L o , and R o is the short circuit (SC) test.…”

Correlation of measured neon soft X-ray pulses of the INTI plasma focus with the reflected shock phase at 12KV

“…14 The dI/dt signal is from a 7-turn Rogowski coil wrapped around one of the 16 conductors returning the current from the focus tube to the capacitor earth. 15 The absorption filters method based on foil absorbers and silicon PIN diode detectors is used in the SXR spectrometer (see Fig. 4).…”