A variety of plasma wave and electric field effects were observed during the AMPTE (Active Magnetospheric Particle Tracer Explorers) solar wind barium release on December 27, 1984. Electron plasma oscillations provided measurements of the electron density during the entire event. Inside the diamagnetic cavity created by the ion cloud, the electron density reached a peak of about 2¿105 cm-3 and then decreased approximately as t-2 as the cloud expanded. A static electric field of about 1--2 mV/m was detected in the diamagnetic cavity. This electric field is in the same direction as the solar wind electric field, suggesting that the solar wind electric field may be able to penetrate into the cloud. As the spacecraft passed through the boundary of the diamagnetic cavity, a region of compressed plasma and magnetic field was detected upstream of the ion cloud with a peak density of about 104 cm-3 and magnetic field strength of 130 nT. This region of compressed plasma is believed to be caused by solar wind plasma and magnetic field lines draped around the nose of the ion cloud. Inside the diamagnetic cavity, electrostatic emissions were observed in a narrow band centered on the barium ion plasma frequency and in another band at lower frequencies. These waves are believed to be short-wavelength ion acoustic waves. Bursts of electrostatic waves were also observed at the boundaries of the diamagnetic cavity, apparently caused by an electron drift current along the boundary. An intense burst of broadband electrostatic noise was observed near the outer boundary of the plasma compression region with intensities of up to 140 mV/m. This noise is apparently associated with a shocklike interaction between the ion cloud and the solar wind. Growth rate computations show that the noise can be accounted for by an electrostatic ion beam-plasma interaction between the nearly stationary barium ions and the rapidly moving solar wind protons.