Following the ideas of R.K. Golka, Y.H. Ohtsuki and H. Ofuruton we made experiments with microwave induced plasma balls. Some researcher think that they could be experimental models of the ball lightning: an interesting and up to now not understanded phenomenon of the nature. The experimental setup consisits of a kitchen microwave oven with a burning candle inside. (SEE the WARNING above before making any experiments!) After switching the power on plasma balls form at the flame and fly upwards. The lifetime of the balls are cca. 0.5s and reaching the wall of the oven they disappear. Sometimes they split into two or more parts before that.

The following pictures show typical snapshots of the experiment. These images were digitally filtered to get rid of the grid of the microwave oven door. To see the original pictures click here .

Some ideas on the experiment

Before the plasma ball forms there is a bright flash at the flame. Probably the electromagnetic field induce arc-light at the carbonized wick producing large number of electrons and ions. These particles together with the ionized particles of the flame forms a cloud that conducts electricity. The microwave can create eddy current (?) in this cloud. This current could prevent the recombination of the ions and electrons. The size of the balls is cca. 3cm that is in good agreement with the theory of P. Kapitza.

Links to other pages:

• The Ball lightning page of Bill Beaty with many links and a good journal reference index
• Candle flames in microgravity by NASA

References:

• Y.H. Ohtsuki, H. Ofuruton: Plasma fireballs formed by microwave interference in air; Nature Vol. 350, pp 139-141, (1991)
• K. Yasui: Plasma fireballs fed by microwaves; Physics Letters A, 173, pp451-455, (1993)

István Csabai & András Czirok , 1997