|MadSci Network: Physics|
When the high voltage is first applied, the electrodes act as a capacitor, which begins to charge up. Most of the charge should be near the tips of the electrodes, as long as the air gap is small compared to the box size. When the electric field strength between the electrodes gets large enough, the air in the gap starts to ionize, and a current begins to flow. This causes the capacitor (i.e. the electrodes) to discharge, and the current between the electrodes rapidly builds up. During this process, the electrodes are acting like a dipole antenna, and radiating electro- magnetic waves. Since the time of this process is about a microsecond, the electromagnetic waves have frequencies around a megahertz. These waves are then absorbed by the steel box. The purpose of the box is to keep the electromagnetic energy confined; otherwise you would be creating a lot of radio static! A steel box is used because steel has a relatively high electrical resistance. Since power absorbed goes like RI^2, having a high resistance keeps the currents in the box lower than if a copper box was used. The amount of electromagnetic energy which is radiated depends on the size and shape of the electrodes (which gives the capacitance), and the temperature and humidity of the air in the box (which gives the breakdown electric field). If you are running 15 amps through the arc lamp, I expect it will get pretty hot! I don't think that the initial transient is a special problem. The lamp will continue to generate electromagnetic waves during its normal operation, due to fluctuations in the current. How do you get the light out of the box? A heavy mesh screen will let most of the light out, while keeping most of the RF energy confined.
Return to MadSci Network