An experimental model of ball lightning

Summary form only given. We have here a study of one possible form of Ball Lightning. In this work, bright orange plasma spheres of several centimeters in diameter were produced in atmospheric pressure air. These spheres persisted for up to a half second after the power supply was turned off. We developed a plasma arc in the form of a disc rather than a line. In this manner, we create a plasma sphere several centimeters in diameter that is confined by atmospheric pressure. It is created over a period of 1/2 a second. The theory is based on the published measurements on energy loss in an electric arc in air. We have a mathematical model for the lifetime of the balls. /spl tau/=6/spl sigma/NL/sup 2///spl nu/(3.16)/sup 2/. Here, /spl tau/ is the lifetime, /spl sigma/ is the atom - atom scattering cross section, N is the gas density at the operating temperature, L is the radius of the sphere, /spl nu/ is the thermal velocity of the gas at operating temperature, and 3.16 is the first zero of the spherical Bessel function. We have many photographs of the ball floating in the air after the power supply was turned off. To obtain the lifetime of the plasma spheres, streak photographs were made, showing the ball´s position versus time. These photographs show lifetimes of up to 1/4 second. Other photographs using a tape recorder showed lifetimes up to 1/2 second. High-speed (1 frame/millisecond) images were taken of the ball using both a digital camera and a high-speed film camera. We increased the size of the ball, by enclosing it in a cone of fused quartz, open at the bottom to reduce heat losses during the time of ball formation. The larger balls produced longer-lived spheres. We have also analyzed the ball´s light with a spectrometer, and found the spectrum appeared to be a continuum with a band in the red and a band in the green. The radiation temperature was measured to be 95/spl deg/F, using a non-contact Infrared thermometer that explains the longer lifetime of the - alls. We emphasize that there are possibly several other forms of ball lightning, such as magnetically confined plasmoids, and ours is just one form of it.