Laboratory studies of magnetic vortices. I. Directional radiation of whistler waves based on helicity injection (vol 6, pg 2989, 1999)

A novel principle for the directional excitation of whistler waves is demon strated in a laboratory experiment. It is based on helicity conservation of electron magnetohydrodynamic fields in plasmas. Whistler wave packets prop agating in opposite directions to a static magnetic field have opposite sig ns of helicity. Injection of helicity of one sign produces radiation in one direction. This is accomplished with an antenna consisting of a loop linke d through a torus. Directionality of 20 dB is readily achieved. The directi on of radiation is electronically reversible. Transmission between two ante nnas is unidirectional, hence nonreciprocal. Possible applications include secure communication, direction finding, and efficient power deposition in radio frequency (rf) heating. (C) 1999 American Institute of Physics. [S107 0-664X(99)01308-7].