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A rod pinch diode (RPD) is a feasible load configuration to generate a high-brightness, small-size hard x-ray radiation source. In this paper, the radiography performance of a wire-shorted low-impedance RPD on a compactly designed table-top driver (WRPD-1) is demonstrated for the first time. The driver consists of four high-power discharge branches connected in parallel, with each branch consisting of two metal-film capacitors and one multigap field-distortion switch in series. The four branches are triggered synchronously to generate a fast-rising current pulse: the inductance of the load section at the short circuit is ∼10 nH, and the short-circuit current amplitude is ∼325 kA at ±90 kV charging voltage, with a 10%-90% rise time of 110 ns. With a low-impedance RPD shorted by an 18-µm-diameter aluminum wire, a quasi-spherical x-ray focal spot with diameter <0.6 mm (width of the half-maximum grayscale) and a pulse duration of ∼25 ns (half-width of the radiation pulse) is obtained at ±70 kV charging voltage, and the imaging resolution excels 10 lp/mm under 1.56× magnification. According to the transmission-absorption x-ray spectrum estimation, the average emitted photon energy is ∼30 keV with a distinct peak in the 10-15 keV range that corresponds to the L-lines of tungsten, and the total energy of photons >10 keV reaches ∼1.16 J. The present results show that the device can serve well for the flash radiography diagnosis and potentially as an efficient light source for dynamic x-ray diffraction., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

The prepulse current is an effective way to optimize the load structure and improve the implosion quality of the Z-pinch plasma. Investigating the strong coupling between the preconditioned plasma and pulsed magnetic field is essential for the design and improvement of prepulse current. In this study, the mechanism of the prepulse current on the Z-pinch plasma was revealed by determining the two-dimensional magnetic field distribution of preconditioned and nonpreconditioned single-wire Z-pinch plasma with a high-sensitivity Faraday rotation diagnosis. When the wire was nonpreconditioned, the current path was consistent with the plasma boundary. When the wire was preconditioned, the distributions of current and mass density presented good imploding axial uniformity, and the imploding speed of the current shell was higher than that of the mass shell. In addition, the mechanism of the prepulse current suppressing the magneto-Rayleigh-Taylor instability was revealed, which formed a sharp density profile of the imploding plasma and slowed the shock wave driven by the magnetic pressure. This discovery is essential and instructive for the design of preconditioned wire-array Z-pinch experiments.

As a new method for generating strong underwater shock waves with rapid repetition frequency, the use of underwater electrical-wire explosion (UEWE) to drive insensitive energetic materials has attracted increasing research attention in recent years. Accordingly, equipment based on this new method have been developed. The ability to measure the stress produced by an UEWE on a device plays a very important role in optimizing the device performance. However, in conventional stress measurements, the spatial electromagnetic interference (EMI) produced by the discharge can affect the measurement accuracy or even damage the experimental instruments. In this study, a novel system for measuring stress in a strong electromagnetic field, based on a piezoelectric film and a conditioning circuit, was debugged and evaluated. Shielding was used to eliminate the intense EMI due to the strong electromagnetic field. Our simulation and experimental results demonstrate that the stress generated can be quickly determined by measuring the output voltage of the conditioning circuit. The new system can be used to measure the stress at the fluid-solid interface under a strong electromagnetic field environment.

The dynamic polarizabilities of Al atom at 19 wavelengths from 420 nm to 680 nm are measured experimentally for the first time. A 15 µm diameter Al wire is heated to the gas/ microdrop stage using a 3 kA, 25 ns pulsed current, and the energy deposition when the resistive voltage reaches its peak is 4.7 eV·atom -1 , which is higher than the atomization enthalpy of Al but much lower than its first ionization potential. Two laser interferometric images of the Al gas are obtained simultaneously using a 532 nm laser and an optical parametric oscillator laser. Then an integrated phase method is used to reconstruct the Al atomic linear density distribution based on the known atomic polarizability at 532 nm, which acts as a bridge between the two interferograms to obtain the relative atomic polarizability value at a specific wavelength with respect to the value at 532 nm. The measured dynamic polarizability of Al atom decreases from 13.5×10 -24 cm 3 to 9.4×10 -24 cm 3 as the wavelength increases from 420 nm to 680 nm with a measurement error of approximately ±10%. The experimental result fits well with an uncoupled Hartree-Fock approximation, and the reconstructed static polarizability of 8.13 ± 0.79×10 -24 cm 3 is well matched with reference measurement results.

In this work, two Faraday channels and one shadow channel are constructed by two non-polarizing beam splitters and one reflector to measure the Faraday rotation distribution. The intensity of the Faraday and shadow images is related to the state of polarization (SOP) of the incident light, thus achieving two-dimensional accurate measurement. The measurement sensitivity is influenced by the settings of two polarization analyzers in the Faraday channels and the parameters of beam splitters, which are explored numerically and verified with experiments. The fluctuation of the probe light is eliminated by using three evaluation indexes. Also, the measurement range and error sources under different experimental settings are discussed.

Measurement of the magnetic field distribution in Z-pinch experiments remains an ongoing challenge. We present a method of measuring the radial distribution of the magnetic field around a copper rod using Zeeman splitting of sodium (Na) emission lines, in which an Na layer is formed by the laser ablation of NaCl crystals on a load surface. The load consists of a copper rod of 2 mm diameter and is pre-covered on its surface by the NaCl crystals. An 8 ns pulsed laser with an energy of 1 J and wavelength of 532 nm is focused on the crystals. The Na plasma is produced and expands from the surface of the copper rod into a vacuum. After applying a pulsed current with a peak value of 375 kA to the load, the Na 3s-3p doublet displays significant Zeeman splitting patterns. The self-luminosity of the Na plasma is recorded by a spectrometer coupled with an intensified charge-coupled device camera from an end-on view to eliminate the effects of different observing angles and Doppler shifts. We determine the magnetic field by fitting the measured spectra with the calculated results of the Voigt profile. The measurable range of radial position is 5-7 mm, and the corresponding magnetic field is 5-15 T. The averaged error of curve fitting is less than 12%.

The physical process of electrical explosion of wires in vacuum is featured with the surface discharge along the wire, which generates the corona plasma layer and terminates the Joule heating of the wire core. In this paper, a fiber-array probe was designed to directly measure the radiation of surface arc with spatial and temporal resolution. The radiation of the exploding wire was casted to the section of an optical-fiber-array by a lens and transmitted to PIN diodes and finally collected with an oscilloscope. This probe enables direct diagnostics of the evolution of surface discharge with high temporal resolution and certain spatial resolution. The radiation of a tungsten wire driven by a positive current pulse was measured, and results showed that surface discharge initiates near the cathode and propagates toward the anode with a speed of 7.7 ± 1.6 mm/ns; further estimations showed that this process is responsible for the "conical" structure of the exploding wire.