The barium explosion of the Condor critical velocity experiment created a complex electric field pulse detected in situ by a single-axis electric field double probe on a separate spacecraft a few kilometers away. The measured component of the pulse had a peak amplitude which exceeded 320 m V/m. The sign of this component was consistent with an electric field pointed back toward the explosion point. The large electric field pulse arrived nearly simultaneously with the fastest minor ions associated with the explosion. Just ahead of the pulse a packet of nearly monochromatic waves (3460 Hz) was detected near the oxygen lower hybrid frequency, with a measured electric field component of 6 mV/m along the double-probe direction. The bulk of the barium beam was accompanied by a quasi-dc electric field whose amplitude was between 100 and 200 mV/m. The E¿B drift associated with this latter field was less than the speed of the main beam estimated fom the time delay of the arrival of the initial beam-related waves and particles. This implies a counterstreaming between the neutrals and ions in excess of the critical ionization velocity for barium. This region of the beam was accompanied by a peaked distribution in the soft electron fluxes and by intense electric field fluctuations with peak (one component) amplitudes exceeding 375 mV/m. The wave frequencies were in the range 0.1fLH≤f≤fLH where fLH is the barium lower hybrid frequency ((&OHgr;i&OHgr;e)1/2/2&pgr;).

The most significant electron heating was associated with the most intense wave activity. The observations provide evidence of several important links which may be required in the critical velocity chain and are consistent with theories which appeal to either the modified two-stream instability or to an ion beam process. For example, the data support the hypothesis that mechanical energy in the beam is converted to electrical energy associated with cross-field currents and that these currents are unstable to lower hybrid wave generation which subsequently heats the electron gas. In principle, the electrons then ionize the neutral gas to complete the loop. The observed (one component) lower hybrid electric field wave intensity was less than that predicted for a fully developed modified two-stream instability, which may be related to the fact that the fastest-growing modes are inhibited by the finite dimension of the beam parallel to the magnetic field. In turn, the reduction in the observed lower hybrid wave amplitude may be related to the low efficiency of the Alfv¿n process in the Condor experiment geometry reported in the companion papers.