The results from the X Ray Bremsstrahlung Experiment of Project Trigger

An ionospheric cesium cloud release experiment, Project Trigger, was conducted at ESRANGE, Kiruna, Sweden, on February 11, 1977. A rocket‐boosted, parachute‐borne X ray bremsstrahlung detector was included in the overall project to accomplish three objectives: (1) an assessment of the preexplosion background precipitation from a slowly moving platform, (2) a measurement that would allow the effective radius of the triggered precipitation region to be determined, and (3) detection of any long‐duration precipitation effects. Analysis of the data produced the following conclusions: (1) with some slight exceptions, the counting rate observed before the explosion was the normal quiet background expected for the experimental circumstances; (2) the counting rate below 20 keV observed after the explosion was considerably in excess of that predicted by existing theoretical calculations of atmospheric X ray production and known cosmic ray sources; there is a possibility that this excess was an effect of the explosion; (3) a 0.13‐Hz peak in the power spectral density of the X ray flux was observed; this observation is interpreted as evidence for a particle‐wave‐particle interaction involving a bounce resonance between 1.5‐keV electrons accelerated by the explosion and 1.7 kHz whistler mode waves, which in turn pitch angle scatter higher‐energy electrons; (4) no prompt effect of the cesium release was seen in the X ray data; and (5) this result sets an upper limit of ∼2.8 km on the effective radius of the triggered prompt precipitation flux tube. This article contains supplementary material.