Using laser shadowgraphy and interferometry on a Qin-1 facility, the initial plasma formation and dynamics of an exploding stainless steel liner were investigated. To obtain the absolute electron density distribution inside the liner, we established continuous wave laser interferometry using a streak camera to measure the shift in the fringes over time. Plasma is generated at the interior wall and flows toward the center with a velocity of ∼100 km/s, thus forming a column with higher density by accumulation. Simultaneously, a high-density plasma layer is formed near the interior surface and this layer flows toward the center at approximately 10 km/s. In addition, magnetohydrodynamics (MHD) instabilities were observed at the exterior surface using side-on laser shadow images at a much later time (∼400 ns). The growth in the amplitude and the wavelength of the perturbations were then analyzed. An MHD simulation of this process was then established to demonstrate that the high-density plasma layer carries part of the current and that it flows within the 10 km/s range after comparison with the experimental results. Finally, we measured the voltage and derived the change in the inductance. The results prove that part of the current flows through the center plasma column, which then influences the subsequent plasma flow.
The main factor that slows down the high-frequency response of a resistive voltage divider (RVD) is the distributed stray capacitance (Cg) between the high-voltage-arm (HVA) and the grounded conductors, due to the charging and discharging of Cg through the high resistance RH of the HVA with characteristic time RHCg. Based on a RVD consisted of ceramic tube resistors, a compensation method utilizing the distributed capacitance between a specially shaped inner conductor and the HVA was proposed in this paper, which is more compact than grading rings and can work well with grounded shielding. The method was verified by electromagnetic simulation, which indicated a bandwidth improvement from 3 MHz to more than 1 GHz for the prototype RVD with grounded shielding. Experimental results showed that the 10%–90% rise time for a step input was improved by the compensating electrode from ∼90 ns to 1.25 ns. The main drawback of the method is the possible degradation of insulation when precise compensation is required.
In this paper, two-dimensional magnetic field structure of a double-wire Z-pinch during the ablation stage is investigated using Faraday rotation diagnosis. The experimental results intuitively display the two-dimensional magnetic field distribution and reveal the process of the global magnetic field spreading towards the load axis as the ablation progresses. The radial current component is determined based on the axial non-uniformity of the magnetic field structure, which further confirms the two-dimensional current path within the ablation stream. Additionally, the significantly enhanced magnetic field intensity and opposing magnetic field direction on both sides of the precursor plasma column indicate the existence of magnetic reconnection and the current layer within. This process also specifically reveals the current transfer process from the wire to the precursor column.
The influences of the prepulse current on the implosion dynamics of planar wire array were investigated. The time-delay between the prepulse current and the main current ( Tdelay) was able to be controlled manually based on the double pulse current generator “Qin-1.” In the precondition stage by the prepulse current, the corona plasma, aluminum vapor, and residual wire cores formed during the explosion of the wires, and ∼40% (±10%) mass of the wires was in a gaseous state at ∼425 ns after the prepulse. After the main pulse was applied, the low-density corona plasma was first imploded and then collided with the aluminum vapor and residual dense cores. Then, the further implosion of the preconditoned wires closely related to their mass distribution, which was determined by the duration of Tdelay. The residual dense wire cores had a significant impact on the implosion when Tdelay was ∼200 ns. When Tdelay increased to ∼> 500 ns, the mass distribution gradually became uniform, and the implosion of the preconditioned wires showed no ablation and no trailing mass.
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%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.