Magnetic pumping of whistler waves by tether current modulation

摘要

Magnetic excitation of whistlers by a square array of electrodynamic tethers isdiscussed. The array is made of perpendicular rows of tethers that carry equal, uniform,and time-modulated currents at equal frequency with a 90° phase shift. The array wouldfly vertical in the orbital equatorial plane, which is perpendicular to the geomagnetic fieldBo when its tilt is ignored. The array radiates a whistler wave along Bo. A parametricinstability due to pumping by the background magnetic field through the radiated wavegives rise to two unstable coupled whistler perturbations. The growth rate is maximum forperturbations with wave vector at angles 38.36° and 75.93° from Bo. For an experimentinvolving a wavefront that moves with the orbiting array, which might serve to studynonlinear wave interactions and turbulence in space plasmas, characteristic values ofgrowth rate and parameters, such as the number of tethers and their dimensions anddistances in the array, are discussed for low Earth orbit ambient conditions.