Plasma‐depleted holes, waves, and energized particles from high‐altitude explosive plasma perturbation experiments

Abstract

High explosive shaped charge experiments King Crab and Bubble Machines I and II, designed to perturb the ambient plasma and magnetic field, were flown above 460 km on Taurus Tomahawk rockets from Poker Flat in March 1980, 1981, and 1982, respectively. The last flights were a mother‐daughter combination with the instrumentation section remaining attached to the rocket. The detectors consisted of a single‐axis dipole electric field detector, a fixed bias cylindrical Langmuir probe, a three‐axis attitude magnetometer, and curved plated energetic ion and electron electrostatic analyzer. The first experiment, King Crab, revealed the existence of a barium plasma depleted region or dark hole of about 5 km diameter centered on the burst. All electric power to the instruments failed on the lift‐off of the 1981 Bubble Machine I, but useful optical data were obtained. The third flight a year later produced useful data from all but the electron detector on the electrostatic analyzer. Ground‐based optical and telluric field instrumentation recorded evidence for injection‐induced waves of about 5‐s period. Delay times indicate a slow (175–385 km/s) propagation from the burst point. Promptly following the release, auroral intensity ion beams were observed in the field‐aligned ion electrostatic analyzer, with energies up to 6.8 keV. Evidence suggests that these particles were not energized by the explosion but that they represent an existing ion conic population pitch angle scattered by the released barium into the view of the detector. Concerning locally produced electrostatic instabilities, the wave measurements of Bubble Machine II indicate that finite Larmor radius stabilization occurs for the weakly driven low (barium) density situation, but that shorter‐wavelength waves can occur early in the expansion event when the barium density is higher. These results are in reasonable agreement with a theory described by Sperling and Krall (1981).