DIRECT-RADIATION FROM A STRONG DC ELECTRIC-FIELD

Simulations have shown that a strong DC electric field yields, after electrostatic transients, a beam of electrons that is nearly flat in velocity distribution yet emits strong electrostatic and electromagnetic waves. Electric energy is converted "directly" into radiation. I derive this radiation analytically in order to learn how the radiation may depend on field strength and beam density in astronomical objects. Any wave with a significant electric component along the DC electric field grows exponentially in time, with the growth rate proportional to the number of electrons in the beam. The lower limits on the DC electric field and the beam density are set by competing plasma processes. The results are related to solar millisecond radio bursts.