No abstract

Observations of substorm‐associated enhancements of proton and electron fluxes were made by Explorer 45 below L = 5.3 in the dusk magnetosphere on February 13, 1972. The particles were observed after a substorm that started at 1116 ± 0010 UT in the wake of an ssc at 0939 and that initiated a small magnetic storm with maximum Dst = 47 γ. The protons in the range between 1 and 40 keV exhibit strong dispersion effects in both energy and pitch angle. The electrons also show dispersion effects above 40 keV, while those below that energy are not observed until the satellite crosses the plasmapause. The observations are interpreted in terms of McIlwain's model electric field E3 and an injection boundary close to or coinciding with the plasmapause. Good quantitative agreement is obtained between the observed and the predicted proton energies and pitch angle dispersions and electron energy dispersions. In view of strong temporal fluctuations in the electron flux, no comparison in pitch angle dispersion of electrons is possible. The conclusion drawn is that in this event protons and electrons were injected at the onset of the substorm more or less instantaneously into the magnetosphere along or above the injection boundary and particles with energies below 10 keV were not convected in from the magnetospheric tail.

A series of 13 sudden increases in the proton flux was observed at L > 8 on the subsolar side of the magnetosphere during August, September, and October 1961. These increases are strongly correlated with the appearance of negative magnetic bays in the auroral zone. The increases exhibit proton intensities of J (>100 kev) ≲ 106 p/cm² sec ster. The particle intensity rise time is of the order of 10 minutes. The protons have strongly peaked energy distributions, and the peak energy decreases with time during a period of about 1 hour from about 300 key to 100 key. The events are interpreted as protons drifting in the earth's magnetosphere after being injected into it on the night side.

A linear relationship between the hourly Dst value and the inverse of the cube of the magnetosphere subsolar distance Rs -8 from Explorer 12 satellite boundary observations has been found to exist for geomagnetically quiet times and slightly disturbed periods. The proportionality constant between the Dst and Rs -8 is found to be 1.40 times the theoretical value predicted by Mead but remains unchanged for different geomagnetic conditions. The only changes are the amount of the field depression due to the ring current registered in the Dst values. The field depression at the earth's surface is found to be -19 • from the quiet time ring current and -44 • from the slightly disturbed time ring current. Mead

Abslract. A column of enhanced density plasma,exceeding the density expected from ionization by primary beam electrons, has been observed in a large vacuum system at low magnetic fields (1 to 1.5 G) and low ambient pressures (10 -6 to 10 -s torr). The peak luminosity of the discharge is about 10 times that of the beam alone, with a radius increase by a factor of 3. In the absence of the discharge, RF emission is observed at 1.1 to 1.2 fc-A strong band of RF noise with upper frequency cutoff at about fc is observed in the discharge mode, along with higher frequency noise at or near the plasma frequency.The onset of the plasma discharge is critically dependent on beam current.The present results agree with observations made at much higher densities and magnetic fields in fusion research studies. There has been difficulty in explaining many of the observational results obtained in rocket flights with modest and high current electron accelerators (Winckler, 1976, 1977). In particular, these include 1) the apparent neutralization of the vehicle under conditions where the return electron flux from the ambient plasma or the beam-produced ionization (based on the classical ionization rate of the local neutral gas) to the vehicle should have been much less than the emitted flux, and 2) the presence of a plasma cloud with increased Te and density surrounding the vehicle (Cartwright et el., 1977). We have recently concluded a series of electron beam experiments in the very large vacuum chamber at Johnson Space Center which can provide a plausible explanation for the flight observations. The experimental configuration is basically similar to that described by Bernstein et al. (1975, 1977) and is shown in fig. 1. The experimental conditions were as follows: 1. A tungsten cathode, convergent flow electron gun was used for most measurements; although the gun perveance is % 1.4x10 -6, the maximum beam currents and voltages employed were 100 ma and 2 kV respectively. The gun was operated DC. A pulsed electron gun was also operated for a short period of time. Although the guns could be isolated electrically, the present measurements were made with both the gun and collector grounded to the chamber walls. 2. A set of three coils have been added around the chamber periphery; the total variation in field strength along the beam path was % 15%. Most measurements were made at total mean field strengths ranging from 1.0-1.45 G. Typical beam injection pitch angles were <20 o . The path length between gun and collector was % 20 m. 3. The base pressure in the system was lx10 -6 torr, consisting primarily of water vapor (30%) and N 2. Increases in pressure to lx10 -s torr were accomplished with the addition of dry N 2.This pressure range corresponds to the altitude range 120-180 km; although rocket-borne accelerators have been flown at higher altitudes it is probable that the rockets are always surrounded by gas clouds of similar density which are produced by outgassing and residual motor exhaust. As shown in fig.