Investigation Into Magnetic Reconnection Formation on Propellant Ignition in Electrical Explosion

In magnetic reconnection, magnetic lines break and reconnect to change their topology to a lower-energy state. This process can liberate stored magnetic field energy and accelerate particles during unsteady explosive events. Here, we report the observations of the magnetic reconnection and kink instability of plasma jet in single wire electrical explosion and their effect on propellant ignition. The results showed that the initial velocity of plasma was ∼2,000 m/s, and when the magnetic reconnection occurred, the velocity increased by ∼400–∼2,400 m/s. The evaluated Alfvén velocity was ∼500 m/s, the Alfvén time was ∼20 µs, and the Lundquist number S = 1.7 × 107. Based on these experimental results and model, the three-dimensional magnetic field topology and its evolution process was evaluated and presented. Furthermore, the magnetic reconnection occurred when its curvature reached a certain value due to the fact that the motion of the current sheet changes the topology of the magnetic field, and then, the plasma jet was accelerated and exhausted. The plasma jet angle was ∼50° in experiment 1, and it was consistent with the calculated results. The resulting magnetic reconnection plays an important role in propellant ignition, which enhances the ignition ability of wire electrical explosion. Furthermore, the results represent a key step towards resolving one of the most important problems of plasma physics and can be used to improve the understanding of wire array explosion and propellant ignition.

Adhesive and Magnetic Properties of Polyvinyl Butyral Composites with Embedded Metallic Nanoparticles

Magnetic metallic nanoparticles (MNPs) of Ni, Ni82Fe18, Ni50Fe50, Ni64Fe36, and Fe were prepared by the technique of the electrical explosion of metal wire. The average size of the MNPs of all types was in the interval of 50 to 100 nm. Magnetic polymeric composites based on polyvinyl butyral with embedded metal MNPs were synthesized and their structural, adhesive, and magnetic properties were comparatively analyzed. The interaction of polyvinyl butyral (supplied as commercial GE cryogenic varnish) with metal MNPs was studied by microcalorimetry. The enthalpy of adhesion was also evaluated. The positive values of the enthalpy of interaction with GE increase in the series Ni82Fe18, Ni64Fe36, Ni50Fe50, and Fe. Interaction of Ni MNPs with GE polymer showed the negative change in the enthalpy. No interfacial adhesion of GE polymer to the surface of Fe and permalloy MNPs in composites was observed. The enthalpy of interaction with GE polymer was close to zero for Ni95Fe5 composite. Structural characterization of the GE/Ni composites with the MNPs with the lowest saturation magnetization confirmed that they tended to be aggregated even for the materials with lowest MNPs concentrations due to magnetic interaction between permalloy MNPs. In the case of GE composites with Ni MNPs, a favorable adhesion of GE polymer to the surface of MNPs was observed.

Discharge and post-explosion behaviors of electrical explosion of conductors from a single wire to planar wire array

This work deals with an experimental study of a Cu planar wire array (PWA) in air and water under the stored energy 300–1200 J. A single Cu wire is adopted as a controlled trial. Four configurations of PWA and a wire with the same mass (cross-section area) but the different specific surface areas (15–223 cm2 /g) are exploded. The transient process is analyzed using high-speed photography in combination with the results of optical emission and discharge. Discharge characteristics revealed that PWA always has a higher electric power peak, early but higher voltage peak, as well as faster vaporization and ionization process than the single-wire case. Two to three times stronger optical emission could be obtained when replacing the single-wire with PWA, indicating a higher energy density state is reached. Phenomenologically, in both air and water, single-wire load tends to develop a transverse stratified structure, while PWA is dominated by the uneven energy deposition among wires. Finally, the synchronism and uniformity of the PWA explosion are discussed.

Preparation of Nano/Micro Bimodal Aluminum Powder by Electrical Explosion of Wires

Electrical explosion of aluminum wires has been shown to be a versatile method for the preparation of bimodal nano/micro powders. The energy input into the wire has been found to determine the relative content of fine and coarse particles in bimodal aluminum powders. The use of aluminum bimodal powders has been shown to be promising for the development of high flowability feedstocks for metal injection molding and material extrusion additive manufacturing.

One hundred kilojoules of energy storage in water wire electric explosion deposition energy study

In this experiment, the electro-explosive deposition energy in water of aluminum-magnesium welding wire model ER5356 at 100 kJ capacitive storage energy was investigated. The loop current and the load discharge voltage during the wire electrical explosion were measured using a self-integrating Roche coil and a capacitive voltage divider, respectively. The physical process of electrical explosion and the energy deposition process were delineated by the measured loop currents and load voltages. The current waveform and load voltage of the electric explosion in water of 1.2 mm-3.0 mm diameter Al-Mg wire at 100 kJ stored energy were measured; the changes of load resistance value, load power and deposition energy of the wire loaded with electric explosion were calculated. The results show that the peak circuit current and peak time point decrease and then increase with increasing diameter, and the minimum value is achieved at 1.6 mm wire diameter; the load voltage and load resistance values gradually decrease with increasing diameter; the load power and total deposited energy of discharge achieve the maximum value at 2.0 mm diameter. At 100 kJ energy storage, there is an optimal range between 1.6 mm and 2.4 mm wire diameter.

Surface discharge during electrical explosion of conductors in strong magnetic fields

In experiments on the electrical explosion of conductors in rapidly growing mega-Gaussian magnetic fields, it was found that at the initial stage of the explosion, “hot spots” up to 500 pieces/mm2 were recorded on the surface. At a later stage, a plasma layer was formed on the surface of the conductor, in which filaments, that is, current channels, were formed. In this work, on the basis of the ecton theory, a model of the development of a surface discharge is constructed. The model makes it possible to estimate, firstly, the magnitude of the current flowing through the surface plasma, and secondly, the thickness of the plasma layer.

The initial stage of the plasma formation at skin explosion of cylindrical conductors

The formation of plasma on the surface of the electrically exploded conductor is a key issue in terms of the energy introduced into the metal substance. The purpose of this work was to study the dynamics of dense plasma formation on the metal surface at magnetic induction values of 200-600 T and its rising rates of (2-6) T/ns. The experiments were carried out on a terawatt MIG generator with current amplitude up to 2.5 MA and rise time of 100 ns. In experiments, skin electrical explosion of cylindrical conductors made of different materials and with different diameters was studied. The formation of plasma on the surface of the conductor was recorded using a four-frame optical camera with an exposure time of 3 ns for each frame. It was shown that when the current increases, “spots” appear on the surface of a cylindrical conductor. These spots are the centers of plasma formation. Later in the time, longitudional plasma channels were registered. In course of subsequent merging of the channels relatively uniform plasma formation occurs. The paper discusses the features of the dynamics of plasma formation as a function of the peak and the rising rate of the magnetic field induction.