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Research Papers

# Experimental Study of Electromagnetic Effects on Solid Copper Jets

[+] Author and Article Information
Patrik Appelgren1

Swedish Defence Research Agency (FOI), Grindsjön Research Centre, SE-147 25 Tumba, Swedenpatrik.appelgren@foi.se

Melker Skoglund, Patrik Lundberg, Lars Westerling, Tomas Hurtig

Swedish Defence Research Agency (FOI), Grindsjön Research Centre, SE-147 25 Tumba, Sweden

Swedish Defence Research Agency (FOI), Grindsjön Research Centre, SE-147 25 Tumba, Sweden

1

Also at the Division of Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, Stockholm, Sweden.

2

Also at the Division for Electricity, Uppsala University, Uppsala, Sweden.

J. Appl. Mech 77(1), 011010 (Sep 30, 2009) (7 pages) doi:10.1115/1.3172251 History: Received October 29, 2008; Revised February 02, 2009; Published September 30, 2009

## Abstract

In this paper we present a study of the interaction between an electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise time, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. An electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data on energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200–250 kA and a rise time of $16 μs$ could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending on the initial electric energy in the pulsed power supply.

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## Figures

Figure 1

Shaped charge with a conical metallic liner surrounded by high explosives (HE)

Figure 2

Formation of a shaped charge jet. The two top left pictures show the shaped charge with its cylindrical casing visible, while the following pictures only show the metal liner and its formation to a jet. Due to its velocity gradient the jet stretches, accompanied by a decrease in diameter. The jet is followed by the slug of much higher mass but with lower velocity.

Figure 3

The pulse forming network with four capacitor modules Ci connected via the pulse shaping inductors Li. Lout is the inductance between the capacitor bank and the transmission line, LTrL is the inductance of the transmission line, LEl/SCJ is the inductance of the electrodes and the jet, RSCJ is the resistance of the jet, and V1, V2, and I1 are the voltage and current probes.

Figure 4

The experimental setup with the shaped charge being fired vertically down through the electrodes into the target. Flash X-ray tubes project a shadow of the jet onto the X-ray film.

Figure 5

Picture of the wooden test stand with a thick steel plate, protecting the electrodes and transmission line from pressure and shrapnel. The cylinder on top of the steel plate absorbs most of the fragments from the shaped charge.

Figure 6

The three flash X-ray tubes protected from shrapnel and pressure by their aluminum casings

Figure 7

Measured current pulse in the 96 kJ experiment

Figure 8

Measured load voltage and capacitor bank output terminal voltages in the 96 kJ experiment. The drop in voltages at the time of trigger is due to the inductance distributed in the system.

Figure 9

Impedance and resistance of the electrodes and jet. The dashed line indicates the average resistance value of 21.6 mΩ.

Figure 10

The energy deposition in jet and electrodes during the interaction time

Figure 11

X-ray pictures of jet disruption at different energies. From the top, 96 kJ, 39 kJ, and 0 kJ is stored in the capacitors. The pictures are taken 36 μs after contact is made by the tip with electrode 2 (the right of the two shadowed areas), except for the lower picture, which is taken 31 μs after contact. The jet tip has moved to a distance of 260 mm from electrode 2 after 36 μs.

Figure 12

X-ray pictures of jet disruption at different energies. From the top, 96 kJ, 39 kJ, and 0 kJ is stored in the capacitors. The pictures are taken 86 μs after contact is made by the tip with electrode 2, except for the lower picture, which is taken 81 μs after contact. The jet tip has moved to a distance of 620 mm from electrode 2 after 86 μs.

Figure 13

X-ray pictures of four jet fragments at 36 μs (left) and 86 μs (center and right) after the jet made contact with electrode 2. The figure in the center depicts the same four fragments as in the figure in the right but from a different angle.

Figure 14

Radial velocity for dispersed fragments in the 96 kJ experiments

Figure 15

Radial velocity of the dispersed fragments versus current level through them at their exit from the electrode region in the 96 kJ experiment

Figure 16

The solid lines show an estimation of radius of the jet 86 μs after the tip made contact with the second electrode, assuming an instant radial velocity of 200 m/s of a segment at the exit of the electrode region (located at 0.4 m on the scale). The estimation is made for jet segments with velocities of 3–7.3 km/s. The X-ray picture of the 96 kJ experiment has been stretched in the radial direction.

Figure 17

The X-ray picture of the 39 kJ experiment with the estimation of the radius of the jet, assuming an instant radial velocity of 130 m/s of a segment at exit of the electrode region

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