Laboratory study of the temporal evolution of the near wake of a conducting body with enhanced secondary electron emission

Summary form only given. The current collection of a negatively biased object during the formation of the near wake of a conducting body was studied. A pulsed plasma source was used to create a streaming plasma with a diameter of 30 cm, a density of <10⁸/cm³, directed energy of <100 eV, thermal energy of 3 eV, and a turn-on time of 5 ms. A biasable, 5-cm-radius disk was inserted in the plasma stream, creating a wake. A sphere with a 0.5-cm radius was placed 5 cm downstream of the disk. The temporal evolution of the current collected by the sphere was measured as the sphere was biased in the range of 0 to -5 kV. The current collected by the sphere was dependent on the relative potential of the disk to the plasma potential as well as on the potential on the sphere. The amount of current collected by the sphere was a factor of 2 larger than that expected from the collection of ions and the expected secondary electron emission. The excess current was due to the emission of up to three secondary electrons for every ion collected and only occurred for strongly negatively biased spheres