The hot plasma environment and floating potentials of an electron‐beam‐emitting rocket in the ionosphere

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Abstract
With an extensive array of particle sensors the plasma environment surrounding the Echo III accelerator payload is studied. From measurements of the thermal ion spectrum, negative payload potentials referenced to the unperturbed ionospheric plasma are obtained. Multiple detectors determined the electron population from a fraction of an eV up to 40‐keV energy. An intense electron population extending up to the energy of injected electrons by the accelerator is produced when the acceleration is turned on. The energetic tail of this population is returned to the payload principally from directions in which the beam was fired, with the most intense fluxes coming from the atmosphere for downward injections of the beam. The atmospheric‐scattered beam and secondary electrons are called ‘quick echoes.’ Electrons of energy less than several keV down to the detector threshold (0.1 eV) are called the suprathermal component. These electrons are produced isotropically around the payload during gun firings and decay away in approximately 32 ms. The largest directional intensities of this component are observed at the higher altitudes. Quick echo electrons are also observed to produce suprathermal electrons when they encounter the payload. The mechanism by which the suprathermal electrons are produced is discussed but remains unknown at the present time. The hot electrons surrounding the accelerator payload during gun injections bring sufficient charge to the payload to neutralize it provided the loss of charge by secondary production on the payload skin is small, presumably owing to a positive payload floating potential during injection. Since the hot population exists for tens of milliseconds after the gun turn off, it results in driving the payload up to 4 volts negative during this time. Secondary production on the payload skin apparently prevents much larger negative potentials after gun turnoff when the payload is immersed in the hot population. Quick echo electrons creating suprathermal electrons around the payload also drive the payload to a few volts negative. This is an important consideration when discussing the origin of the suprathermal electrons, since electrical discharge and beam plasma discharge mechanisms do not apply to the quick echo beams.