Energetic ion and electron observations were made from a high altitude sounding rocket launched into the expansive phase of an auroral substorm near local midnight. In the 400‐500 km altitude range, on both the up‐ and down‐leg, intense (∼108 cm−2 sec−1 sr−1 keV−1) beams of 90‐500 eV ions were observed at 90° pitch angles. At higher altitudes the beam appeared at larger pitch angles, the variation of these pitch angles with height being consistent with adiabatic expansion of a population injected at 90° at lower altitudes. The width of the beam was within the angular response (∼10°) of the ion sensor at all energies and altitudes. These ions, energized up to 500 eV, were observed throughout the flight, enhancements occurring at the edges of auroral precipitation regions and, for the largest event, in coincidence with intense field‐aligned electron precipitation. Acceleration by ion cyclotron waves produced via a current‐driven or beam‐plasma instability is suggested as a possible source mechanism.
Further laboratory measurements of the beam‐plasma discharge (BPD) produced when an energetic electron beam traverses an initially neutral gas are presented. The experimental data indicate that the critical beam current Ic at energy V, magnetic field B, and system length L required for ignition obeys the empirical relationship Ic ∝ V3/2/B0.7 PL at pressures P < 2 × 10−5 torr. This relationship appears to primarily describe the accumulation of ambient plasma density, collisionally produced by the beam itself, to a critical value where ωpe² ≈ ωce² at which ignition occurs. Additional measurements of the narrow‐band cyclotron‐related waves (fce < f < 1.4fce) observed at beam currents below BPD threshold do not clearly establish whether this instability is a necessary precursor to the BPD. The relevance of these experiments to past and planned electron beam experiments in space is briefly discussed.
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.
We report energetic ion and electron, wave, and ambient plasma observations from two sounding rockets which were launched from Churchill, Canada, into the expansive phases of two auroral substorms and which passed through source regions of transversely accelerated ionospheric ions (TAI). The two events were observed at low altitudes (400-600 kin) and resulted in ion energization of hundreds of electron volts. In the acceleration region, the ionospheric ion velocity distribution function in the direction perpendicular to the local magnetic field (lB) displayed a distinct, non-Maxwellian, high-energy tail, suggesting ion cyclotron heating. The plasma density was lower than theoretical quiescent values, by as much as 2 decades in the stronger event. Strong thermal ion drift was observed in the perpendicular (lB) direction, but was absent in the parallel (liB) direction. Large-amplitude, low-frequency fluctuations in plasma density were present, and a number of wave modes were observed, including upper hybrid and Langmuir waves, and whistler, ion acoustic, and ion cyclotron waves. No consistent correlation existed between the energetic particle precipitation and the TAI. However, strong field-aligned electron enhancements were observed at times coincident with the TAI acceleration region. The characteristics of the TAI ion energy spectra were consistent with a simple model of ion cyclotron acceleration and energy loss due to ion-neutral collisions. These observations are discussed in terms of current theories on electrostatic ion cyclotron acceleration and lower hybrid acceleration. concluded from their S3-3 data that, at least for O + conics, a substantial fraction of the ion energy originated from transverse acceleration. Gorney et al. [1981] found that conic source regions, estimated by mapping the pitch angles of the peak measured fluxes in conics down to their magnetic mirror points, tended to be below 3000 km. These authors also found that perpendicular conics (conics with peak fluxes within a few degrees of 90 ø and also referred to as transversely accelerated 341 ions, TAI) were observed primarily in the 1500-to 2000-km altitude region.In this paper, we report particle, wave, and ambient plasma observations from two sounding rockets which passed through such conic source regions. The events were observed at low altitudes (400-600 km) and resulted in ion energization of hundreds of electron volts. EXPERIMENTSBlack Brant rockets AAF-IVB-33 and AAF-IVB-36 were launched from Churchill Research Range, Manitoba, Canada (58.74øN, 93.82øW) into the expansive phases of two auroral substorms, IVB-33 on February 5, 1976, at 0522:55 UT (2322:55 LT) to an apogee of 735 km and IVB-36 on January 26, 1981, at 0720:06 UT (0120:06 LT) to an apogee of 585 km. Both payloads were instrumented with electrostatic analyzers to measure electron and ion spectra in the 0.1-to 20-keV/q range, solid state detectors to measure energetic particles (E > 20 keV/q), low-energy ion sensors to measure ambient ion velocity distributions (0.1-5 ...
A proportional counter has been designed to detect soft beta-emitters in the gas phase. Data is presented to illustrate the applicability of the counters to the detection of C14, S35, and H3. Various partial pressures of C14O2 have been investigated to determine the effects on the counter properties. Corrections have been made for the counter ends and the memory effects are described. An energy spectrum is presented for H3 to determine the low energy limit of the instrument.
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