Abstract
For a hybrid X-pinch load assembled in parallel with the return-current rods, the impedance of the hybrid X-pinch load is important for current division between the load and the current rods. In this paper, the experimental results of the investigation of the impedance of a hybrid X-pinch load on the Qiangguang facility (1.5 MA, 100 ns) were reported. The current of the X-pinch load was measured using a serial nickel foil resistor, and the voltage was measured using a two-stage resistive divider. The inductance of the X-pinch load was obtained by comparing the differential signal of the current with the voltage waveform, and it is about 4.7 nH, which is nearly equal to the calculated total inductance of the metal wire and the two X-pinch electrodes. The resistance of the X-pinch was determined by subtracting a part of the inductance from the measured voltage, and the following results were obtained. At the start of the current, the resistance of the X-pinch increases quickly from the metallic resistance of 0.16 Ω at room temperature for a 2-mm-length 30-μm-diameter Mo wire to 0.8 Ω in about 10 ns, and then, it falls fast to nearly zero, which suggests that the electrically exploding phase of the metal wire ends and the high conductive plasma is formed. As the current continues to flow through the Mo wire, the resistance increases once again from nearly zero to about 0.4 Ω at the moment when the X-pinch begins to burst x-ray radiation, which reflected that the micro-pinch dynamical process occurs and a hot and tight plasma zone is formed. Assuming that the tight plasma zone is 300 μm long with a 10 µm diameter and the temperature of the plasma is ∼1 keV, we can obtain that the resistance of the tight X-pinch spot is about 0.6 Ω, which is close to the value of 0.4 Ω obtained in the experiments.
Highlights
X-pinch loads can emit x rays at the wire crossed zone as point projection radiography for the x-ray sources of few-micrometer size
When the X-pinch is used as a back-lighting x-ray source in wire-array Z-pinch experiments, it is usually assembled in parallel with the return-current rods; sometimes, even two or three X-pinches are assembled in order to obtain time-resolved x-ray back-lighting images in one shot,9 and the load current will be distributed between the X-pinch loads and return-current rods
The typical voltage and current signals of a Mo X-pinch are shown in Fig. 6, together with x-ray signals monitored by a diamond photo-conducting diode (PCD) with a 50-μm Cu filter
Summary
X-pinch loads can emit x rays at the wire crossed zone as point projection radiography for the x-ray sources of few-micrometer size. It can be used as a primary diagnostic method for radiography in plasma physics, phase-contrast imaging of soft biological objects, and more.. The return-current rods can be treated as lumped inductance while the impedance of the X-pinch load involving inductance and resistance is not known, so it is necessary to obtain the impedance of the X-pinch load. The current of the X-pinch load is monitored using a metal foil resistor in series with the X-pinch load, and the voltage is measured using a two-stage resistant divider. The paper provides a detailed description of the experimental configuration, the current and the voltage measurement sensors as well as their calibration, the experiment and the results, and, at last, a brief conclusion
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