Some aspects of the interaction between metal bodies and streaming rarefied plasmas were studied in a newly constructed Plasma Wind Tunnel as part of an attempt to investigate (via simulation) phenomena relevant to the spacecraft/space plasma interaction. Detailed nearwake ion current profiles for both spherical and cylindrical bodies at different body potentials (&) and at different plasma flow parameters are presented. Various features of the profiles can be correlated, at least qualitatively, with both plasma and body characteristics. For example, the width of the wake zone appears proportional to the Debye length (&,) and depends on the potential of the target body although it appears to be relatively insensitive to the ratio S = Vnor/(2kT,/M+)1'a. The amplitude of the ion current peak(s) also appears proportional to & while, for hxed #a, the location of the peak is directly related to Sand possibly dependent upon body geometry. The general importance of body geometry is qualitatively demonstrated. In addition, a discussion of the relevance of the above studies to previous in situ data obtained from the Ariel I and Gemini/Agena missions is given.

A parametric study was performed of electron temperature variation in the wake of a conducting sphere in a streaming plasma. The flow conditions were varied as follows: the ambient electron temperatures in the range 850-2450 K; the ambient electron densities in the range 5 x lo'-7 x 106/crn*; and body potentials relative to plasma potential in the range of + 1.7 to-2.8 V for an ion beam energy of-4 eV. Electron temperature enhancements were observed which ranged up to 200 per cent above ambient in the nearest proximity of the body surface. The magnitude of the enhancement depends upon the ambient dennty, temperature and body potential.

The fields and forces along the axis of an acoustic levitation device were measured and characterized. The device consisted of a St. Clair generator and reflector arranged in a single-axis configuration. A significant (i.e., factor of four) enhancement in the levitation forces was obtained by using concave surfaces for the driver and reflector. For bodies of various sizes and geometries, the acoustic levitation force is roughly proportional to body volume until the characteristic ’’diameter’’ reaches ∼λ/2(λ=wavelength). In addition, the behavior of materials when in the liquid state was studied. Liquid drops were found to deform and generally rupture when a characteristic size was reached. The characteristic radius appears to depend on material parameters and is from 0.2–0.5 cm for most materials on the ground.

This paper contains the results of measurements to determine the absolute counting efficiencies and pulse height distributions of a continuous channel electron multiplier (Spiraltron) used in the detection of hydrogen, argon, and xenon ions. The technique involves the post-acceleration of 8-eV ion beams to energies between 100 and 4000 eV. The absolute counting efficiency versus effective ion energy for the ions H2+, A+, and Xe+ is given. The Spiraltron was operated in a marginally gain saturated mode to investigate the charge pulse distribution for the three ions H2+, A+, and Xe+ at ion energies of 3 keV. The pulse height distribution for the light ion H2+ peaked near an equivalent gain of 2×107, while the distributions for the heavier ions displayed no significant peaks. This study suggests that discrimination between light and heavy ions may be accomplished in the energy range E<2 keV by utilizing continuous channel electron multipliers.

NZSLP FIG. 2. A SCHEMATIC COMPARISON BETWEEN THE 'QUASI-PERIODIC EMISSION' EVENT OF 4 MAY 1967 AND A WNG PERIOD pC RFCORDED IMMEDIATELY AFTERWARDS. THE EMISSION WAS RF.-CORDED AT DUNEDIN WHRST THE pc WAS RECORDED ~150 km SOUTHWEST OF DUNEDIN. The 15 min pc shown in Fig. 2 is then probably a ground-level manifestation of the geotail oscillations which had previously produced the plasma bunches responsible for the 'qua+periodic emission'. Thus it appears that the micropulsation 'quasi-periodic emission' under discussion can be adequately explained; though it is indeed a pity that these interesting events are not as common as their VLF counterparts.