Dual Secondary Ball Lightning Tesla Coil

Click to view TRA's Replication (Dual secondary TC)

Click to View Nele Kovacevic's "Fireball" Tesla Coil

Kenneth L. Corum and James F. Corum Corum & Associates, Inc. 8551 State Route 534 Windsor, Ohio 44099

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Experimenter's Narrative:

"...it became apparent that the fireballs resulted form the interaction of two frequencies, a stray higher frequency wave imposed on the lower frequency oscillations of the main circuit.... This condition acts as a trigger which may cause the total energy of the powerful longer wave to be discharged in a infinitesimally small interval of time and the proportionately tremendously great rate of energy movement which cannot confine itself to the metal circuit and is released into surrounding space with inconceivable violence.

It is but a step, from the learning how a high frequency current can explosively discharge a lower frequency current, to using the principle to design a system in which these explosions can be produced by intent." -N. Tesla


Following Tesla's instructions, we rewired our apparatus as two synchronously pulsed high power RF oscillators, the first at a frequency of 67 KHz and the second at 156 KHz (The exact frequencies aren't critical). The basis for the apparatus was first conceived and patented in 1897 by Nikola Tesla. The idea of using two oscillators in synchronism was also used by Tesla at the turn of the century in a patented primitive spread spectrum communication system. The apparatus can be seen in dozens of photographs and circuit diagrams in Tesla's Colorado Springs Notes (referred to as CSN below).

There have been many descriptions and analyses of Tesla's oscillators. The classic being the Oberbeck in 1895. However, all of these scientific and engineering descriptions fall short of a true description. It wasn't until we applied slow wave transmission line theory and partial coherence to Tesla's oscillator that we were able to accurately predict the operation of the oscillator and the subsequent production of fireballs.

The apparatus consists primarily of two one-quarter wavelength, slow wave helical resonators above a conducting ground plane. Both of the resonators were magnetically coupled by a common link to a spark gap oscillator, of high peak power (approximately 70 KW), operating at a frequency of 67 KHz. The actual average power being delivered to the high voltage electrode was on the order of 3.2 KW (2.4 megavolts RF). Tesla, of course, was running about 100 items the power which we could produce with our rather modest equipment.


The spark gap oscillator was set to 800 pulses per second and the duration was 100 microseconds. The low frequency coil had a coherence time of 72 microseconds. This means that the induced incoherent oscillations on the resonator took 72 microseconds to build up a standing wave (or interference pattern), and show up as a high voltage on the top end of the resonator: Vmax = S V min (where S is the VSWR) [The theory is developed in great detail in References 5,6,7. Reference 8 even provides a computer assisted tutorial.] The high frequency coil had a coherence time of 30 microseconds.

#1. Using the high frequency coil to arc to the low frequency coil, the low frequency coil would then release its energy rapidly, in a burst. The burst of energy released manifests itself in the shape of a ball or "bubble." Due to the faster voltage rise on the high frequency coil and the subsequent short duration arc to the low frequency coil, the low frequency now sees a a low impedance where it would normally see a high impedance. the energy trapped in the coil when the oscillator was on must now be dissipated very quickly at this lower impedance point, hence the burst. (See CSN page 114, bottom paragraph. Tesla's use of lumped circuit Q is somewhat misleading, but his physics is substantially correct. Circuit 4 on page 115 and the one on the top of page 174 are virtually the same as Figure 1.)

#2. A second method of fireball production includes the use of microscopic vaporized metal or carbon particles. We used the low frequency coil alone and deposited a thin film of carbon particles on the high voltage electrode. When the voltage began to rise on the end of the resonator, streamers began to form on the electrode. The current passing through the carbon film tended to rapidly heat the carbon particles. This dissipation of power also tends to quickly reduce the impedance and subsequently release all the power rapidly into this heated micron size "resistor." The same results may be gotten by using "the tip of rubber covered cable or sire #10" to "facilitate the pumping of the spark." (CSN page 173-174) Old fashioned rubber is loaded with soot.

Experimentally, we have determined the ideal set of conditions for producing electric fireballs. They are:

1. Generate a lot of carbon or vaporized metal particles in a small region of space.

2. Create large electric fields in the same vicinity (on the order of 1 to 2 MV/m).

3. Rapidly elevate the temperature of the particles.

Video tape easily documents the results of meeting these three conditions. From this, fireball lifetimes are deduced to be 1 to 2 seconds and dimensions are 1 to 3 centimeters in diameter. Also, these are in agreement with Tesla's observations and conclusions. For example, in one place he attributes fireballs to the presence of resistively heated material in the air. (CSN page 333)

This mechanism is consistent with Zaitsev's relatively recent theory in which the resistive heating of particles creates a glowing region or fire ball: "the current of the preleader stages of the discharge from the seed [cloud of fine particles (metal, soot, or ash)] flowing through the structure drives it to thermal explosion." (ref. 1) The fire balls disappear either when the particles burn up or when a thermal explosion occurs. we have observed both.


Using these methods for producing the fireballs, we then set about creating conditions as described by observers of ball lightning. By having the streamers, produced by the two resonators operating together, strike a windowpane surrounded by a wooden frame, we produced conditions normally found in nature. (see refs 2 &3) What was observed by the operator of our apparatus was astounding! "the streamers went from the high voltage terminal and struck the windowpane. There were many fire balls present between the electrode and the window. But where the streamers hit the glass, there were many fireballs emanating from the opposite side of the glass. The fireballs would then travel slowly horizontally 12 inches or so and flare up. Some would travel out a bit farther and explode." .

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These results are reproducible on demand.