Study of Ball Lightning Generated by Electromagnetic Wave Localization

Ball lightning that is a natural phenomenon behaves curiously and moves variously according to a huge amount of eyewitness reports. The ball lightning could be reproduced by an alternative experiment that was the result of a localized spherical plasma object (fireball) caused by microwave interference and discharge inside the cavity. In the experiment, the motion of the plasma fireball was exceedingly similar to that of ball lightning in nature. When we try to understand the generation mechanism of the localized microwave discharge, electromagnetic wave localization gives a strong model. We showed the relationship between the electromagnetic wave localization and the appearance of plasma fireball, numerically and experimentally. In this paper, we discuss the possibility of the natural ball lightning generated by the electromagnetic wave localization from the result of the artificial plasma fireball. INTRODUCTION Ball lightning, luminous object, that is a natural phenomenon under the atmospheric environment behaves curiously and moves variously according to a huge amount of eyewitness reports [e.g. Singer, 1971; Barry, 1980; Stenhoff, 2000]. Kapitza [1955] suggested that ball lightning should appear at the antinodes of electromagnetic waves in radio frequency band between the earth and thunderclouds. The ball lightning could be reproduced by an alternative experiment that showed a localized spherical plasma object caused by microwave interference and discharge inside the cavity, reported by Ohtsuki and Ofuruton [1991]. In the experiment, the motion of the plasma fireball was exceedingly similar to that of ball lightning in nature such as going up, down, left and right, moving against the wind, passing through windows without damaging and so on. When we try to understand the generation mechanism of the localized microwave discharge according to Kapitza’s proposal and the mode theory of the electromagnetic waves in the cavity, the highest intensity of electromagnetic field to potentially cause microwave discharge should be produced at the antinodes in the cylindrical cavity. In Kapitza’s proposal, however, it can be shown that microwave discharge cannot take place because the intensity of microwave at the antinode is only four times as large as that of the incident microwave and is not enough to make discharge. Therefore, we needed to understand how to obtain the high intensity of the microwave to produce the plasma fireball. REPRODUCTION EXPERIMENT At first, we tried to follow and reproduce the experiment of ball lightning according to Ohtsuki and Ofuruton [1991] as shown in figure 1, and then clear its experimental properties of the plasma fireball. In the experiment, a cylindrical cavity made of punched aluminum plate, of which diameter was approximately 161 [mm] and length was 400 [mm], was connected to the waveguide. A plasma fireball existed during microwave supply (a few kW) only when we used slightly distorted cavity. Figure 2 shows the plasma fireball. From this experiment, we found that the motion of the plasma fireball was extremely complicated such as going up, Figure 1. Schematic diagram of experimental apparatus for creation of plasma fireball(s) in a cavity by using microwave. This system is almost equivalent to the experiment by Ohtsuki and Ofuruton [1991]. Figure 2. An example of a plasma fireball in a cylindrical metal cavity. The end of the waveguide, from which the microwave radiated into the cavity, is seen in the center of the cavity (a black rectangle). down, quickly moving to left and right, and oscillating, which corresponded to the eyewitness reports. ELECTROMAGNETIC WAVE LOCALIZATION Although our experiments can reproduce the eyewitness evidence, we have fundamental question: How to generate higher intensity of electromagnetic waves in a restricted region even if electromagnetic wave source exists? We have tried to confirm experimentally and numerically the possibility of realizing the localized microwave for our 2.45GHz microwave in one-dimensional system. Detail experiment and calculation were discussed and shown in the paper of Kamogawa et al. [1999]. The waveguide H01 mode was used here and the complete one-dimensional system was constructed for the easy comparison between the numerical result and the experimental one. In the experiment, a 2.45 GHz microwave oscillator (magnetron) was also used. This microwave radiation was guided through a rectangular waveguide. The power of incident microwave was continuously 2kW. Ceramic plates (2.25 mm thickness) for the multi-scattering of the microwaves, which were the same size as the cross-section of the waveguide, were put in the waveguide. The direction of the propagation of the microwave was perpendicular to the ceramic plates. From this fundamental experiment as shown in the paper [Kamogawa et al., 1999] by using a few ceramic plates, the experimental parameters such as the dielectric constant of the ceramic plates, some effects of this experimental system could be determined Finally, by using the parameters obtained by this fundamental experiments, the predicted mode of the microwave localization could be calculated. One-dimensional disordered system such as a quasi-fractal system (Cantor bar-like) could be calculated. In the system, it was found that the intensity of the microwave was considerably enhanced in restricted regions. Sometimes the enhancement of intensity exceeded a hundred times as shown figure 3. Finally, it could be concluded that the appearance mechanism of the plasma fireball in our whole experiments was high-possibly related to the localization of the electromagnetic waves when we regarded the cavity roughness as this disordered system. CONCLUDING REMARKSOur experiments of 2.45 GHz microwave interference inside the cavity could correspondingly reproducethe eyewitness reports and observation results. Furthermore, we experimentally and theoretically showlocalization of electromagnetic waves in quasi-fractal system and can explain how to obtain higher intensity ofthe electromagnetic wave. Therefore, it is concluded that the appearance mechanism of such phenomena mightbe related to the localization of electromagnetic waves. REFERENCESBarry, J.D., Ball Lightning and Bead Lightning, Plenum Press, New York, 1980.Kamogawa, M., H. Tanaka, H. Ofuruton, and Y-H. Ohtsuki, Possibility of microwave localization to produce aplasma experimental fireball, Proc. of Japan Acad., 75 Ser. B, 275-280, 1999.Kapitza, P.L., O priode sharovoy molnii, Dokl. Akad. Nauk. (in Russian), 101, 245-248, 1955, On the nature ofball lightning, On the nature of ball lightning (English translation), Collected Papers of Kapitza, Vol.2, ed. D.TerHaar, Pergamon, New York, 776-780, 1965. Ohtsuki, Y-H., and H. Ofuruton, Plasma fireballs formed by microwave interference in air, Nature, 350, 139-141,1991.Singer, S., The Nature of Ball Lightning, Plenum Press, New York, 1971.Stenhoff, M., Ball Lightning, Kluwer Academic / Plenum Publishers, New York, 2000.Tanaka, K., and M. Tanaka, Is ball lightning "Anderson Localization"? : Localized and enhanced fields in acorridor with irregular-shaped metal walls, Appl. Phys. Lett., 71, 3793-3795, 1997.Figure 3. Electromagnetic wave localization inquasi-Fractal system.