Skin explosion of double-layer conductors in fast-rising high magnetic fields

Chaikovsky, S. A.; Oreshkin, V. I.; Datsko, I. M.; Labetskaya, N. A.; Ratakhin, N. A.

doi:10.1063/1.4871719

Cited by 45 publications

(6 citation statements)

References 30 publications

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“…The temperature range where all of the spectral features could have been observed simultaneously was 2-2.5 eV. This is consistent with previous electrode-plasma temperature estimates at these linear current densities (0.1-1 MA=cm) [57][58][59].…”

Section: B Density and Temperaturesupporting

confidence: 91%

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Gómez

Gilgenbach

Cuneo

et al. 2017

Phys. Rev. Accel. Beams

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The Z pulsed-power generator at Sandia National Laboratories drives high energy density physics experiments with load currents of up to 26 MA. Z utilizes a double post-hole convolute to combine the current from four parallel magnetically insulated transmission lines into a single transmission line just upstream of the load. Current loss is observed in most experiments and is traditionally attributed to inefficient convolute performance. The apparent loss current varies substantially for z-pinch loads with different inductance histories; however, a similar convolute impedance history is observed for all load types. This paper details direct spectroscopic measurements of plasma density, temperature, and apparent and actual plasma closure velocities within the convolute. Spectral measurements indicate a correlation between impedance collapse and plasma formation in the convolute. Absorption features in the spectra show the convolute plasma consists primarily of hydrogen, which likely forms from desorbed electrode contaminant species such as H 2 O, H 2 , and hydrocarbons. Plasma densities increase from 1 × 10 16 cm −3 (level of detectability) just before peak current to over 1 × 10 17 cm −3 at stagnation (tens of ns later). The density seems to be highest near the cathode surface, with an apparent cathode to anode plasma velocity in the range of 35-50 cm=μs. Similar plasma conditions and convolute impedance histories are observed in experiments with high and low losses, suggesting that losses are driven largely by load dynamics, which determine the voltage on the convolute.

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Section: B Density and Temperaturesupporting

confidence: 91%

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Gómez

Gilgenbach

Cuneo

et al. 2017

Phys. Rev. Accel. Beams

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show abstract

“…As the rate of rise of the magnetic field is increased, the magnetic induction, responsible for the formation of plasma, increases and tends to the value found in the plane geometry. The simulation results agree well with the experimental data [4,15,16], suggesting an adequacy of the used model.…”

Section: Simulation Results and Comparison With Experimental Datasupporting

confidence: 79%

Numerical simulation of electrical explosions in megagauss magnetic fields

Oreshkin

Chaikovsky

Khishchenko

et al. 2017

J. Phys.: Conf. Ser.

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Abstract. The paper reports on a magnetohydrodynamic simulation of electrical explosions of conductors in megagauss magnetic fields. It is shown that in a plane geometry, the time of plasma formation at the surface of a metal conductor does not depend on the rate of rise of the magnetic field and is determined by the properties of the metal; the absolute values of the magnetic field at which plasma is formed are 5±0.25 MGs for copper, 4.25±0.2 MGs for tungsten, 3.85±0.15 MGs for aluminum, and 3.6±0.25 MGs for titanium. In cylindrical geometry, the time of plasma formation does depend on the rate of field rise. IntroductionThe electrical explosion of conductors (EEC) has been studied for a long time and has a number of practical applications. An EEC mode of interest in the generation of superstrong magnetic fields and in the energy transfer, using vacuum transmission lines, is the current skinning mode [1][2][3][4]. For this mode, the time of energy delivery to the conductor is shorter than, or comparable to the time of magnetic diffusion into it. The basic processes inherent in the current skinning mode are the propagation of a nonlinear magnetic diffusion wave [5], the formation of a low-temperature plasma at the conductor surface, and the development of thermal instabilities [6,7].Nonlinear magnetic diffusion features, a speed of field penetration into a conductor are anomalously high compared to a conventional magnetic diffusion. The high diffusion speed is related to a decrease in conductivity of the metal due to its heating by an electric current. A nonlinear diffusion can occur only in a rather strong magnetic field whose induction, for the fairly often used metals, should be not lower than 250-450 kGs [1,2].

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“…[2][3][4][5][6][7] It was shown that depending on the current density, different modes of wire explosions can be obtained, i.e., "slow" explosion (j 10 7 A/cm 2 ) when magneto-hydrodynamic (MHD) instabilities have enough time to develop or, for significantly larger current densities, "fast" explosions, characterized by the development of thermal instabilities. [8][9][10][11][12] For fast explosions, if the skin time is significantly shorter than the current rise time, the explosion can be considered volumetric. On the other hand, an explosion is considered "superfast," when the skin-layer thickness is much smaller than the wire radius.…”

Section: Introductionmentioning

confidence: 99%

Phase transitions of copper, aluminum, and tungsten wires during underwater electrical explosions

et al. 2018

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Using streak images of underwater electrically exploding copper, aluminum, and tungsten wires (current densities of 10 7-10 8 A/cm 2 and energy density deposition of 10-50 kJ/g) and generated weak shocks, the onset of each phase transition, its duration, and the time when the wire explosion occurred were determined. The measured discharge current and resistive voltage were used to calculate the energy and energy density deposition. Using the discharge current waveform and the onset of the strong shock wave, the specific action integral was calculated and compared with published data. The thermodynamic parameters during the wire explosion were calculated using one-dimensional magneto-hydrodynamic simulations coupled with equations of state for water, copper, and aluminum. It was shown that the onset times of weak shocks, in general, cannot be related to the melting or the evaporation of the entire wire.

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Skin explosion of double-layer conductors in fast-rising high magnetic fields

Cited by 45 publications

References 30 publications

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Numerical simulation of electrical explosions in megagauss magnetic fields

Phase transitions of copper, aluminum, and tungsten wires during underwater electrical explosions

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