PROPAGATION OF BEAM-DRIVEN VLF WAVES FROM THE IONOSPHERE TOWARD THE GROUND

As part of the Cooperative High Altitude Rocket Gun Experiment (CHARGE -2B) rocket mission, an electron beam was injected into the ionosphere with a modulated beam current in an effort to generate very low frequ ency (VLF) waves. The propagation of the beam-driven VLF waves through the ionosphere is examined here to determine whether it is possible t o detect these wave emissions with ground receivers. The paths of the VLF waves from where they were generated near the rocket were followed to the bottom of the ionosphere and the decrease in wave amplitude du e to wave-particle resonance and collisional damping was calculated. I t was found that due to collisional damping, which for these VLF waves becomes large at altitudes below about 150 km, wave amplitudes were d ecreased below the background atmospheric noise level. A number of dif ferent beam injection events have been examined and in all of the case s studied the waves were sufficiently damped such that detection on th e ground would not be possible. This is in agreement with observations on the ground in which no wave emissions were observed during the CHA RGE-2B mission. Control parameters that would be more favorable for be am-generated VLF propagation to the ground are discussed for future ex periments of this type.