In the large vacuum facility at the NASA‐Johnson Space Center an electron beam was projected ˜ 20 m parallel to B from a gun with variable accelerating potential (1.0 to 2.5kV) to an aluminum target. The ionospheric neutral pressure and field were approximated. Beam electron energy distributions were measured directly using an electrostatic deflection analyzer and indirectly with a detector that responded to the X‐rays produced by electron impact on the target. At low currents the distribution is sharply peaked at the acceleration potential. At high currents a beam plasma discharge occurs and electrons are redistributed in energy so that the former energy peak broadens to 10‐15 percent FWHM with a strongly enhanced low energy tail. At the 10% of maximum point the energy spectrum ranges from < ½ to ∼ 1.2 times the gun energy. The effect is qualitatively the same at all pitch angles and locations sampled.
A space qualified 260" spherical plate electrostatic analyzer has been developed as a plasma diagnostic tool. The use of nested spheres and unusually shaped microchannel plates has resulted in a sensor capable of measuring simultaneously the three-dimensional populations of ions and electrons in a plasma. High-current microchannel plates and a new packaging of a hybrid preamplifier discriminator are combined with an uncommon highvoltage circuit. The combination of these features yields an analyzer that is compact and lightweight, efficient in its power consumption, and has-a broad dynamic range.
Recent electron beam injection experiments in the lower ionosphere have produced two perplexing results:
1. At altitudes from 140 km to 220 km, the beam associated 391.4 nm intensity is relatively independent of altitude despite the decreasing N2 abundance.
2. The radial extent (⊥B) of the perturbed region populated by beam associated energetic electrons significantly exceeds the nominal gyrodiameter for 90° injection.
A series of laboratory measurements is described in which both of these flight results appear to have been closely reproduced. The laboratory results are reasonably consistent with the transition from a collision dominated to collisionless beam‐plasma discharge configuration.
We have developed a new compact thermal ion sensor suitable for spaceflight or laboratory applications. The device is highly sensitive and has a wide dynamic range due to its use of a microchannel plate charge multiplier. It allows spatial variations in velocity and anisotropic temperatures to be measured in a flowing plasma stream using a segmented anode. It has a high rejection to solar UV due to the trajectories of the particles within the device. The device has been flight tested as part of the Charging Hazards and Wake Studies flight experiment and sample data from the flight are presented. We discuss interpretation of the output of the device including extracting the parallel and perpendicular temperatures and the flow energy of a plasma stream.
A system has been developed to provide accurate calibration of electron detectors measuring in the energy range from approximately 10 eV to 50 keY. The principal component of the system is a large area (730 cm 2 ), monoenergetic electron beam which is tunable in energy. This beam is produced by illuminating, in vacuum, a thin gold film deposited onto a quartz flat with ultraviolet light, such that photoelectrons are ejected from the gold surface. With the gold film floated at an adjustable negative voltage, the photoelectrons ejected from the surface are accelerated towards an electrically grounded screen which is positioned in front of the quartz flat. All high voltages in the beam system are guarded so as to eliminate any significant leakage current. The current leaving the gold surface which determines the beam intensity is measured using a specially designed picoammeter. Electron beam intensities of _10 6 electrons/cm 2 s are produced by illuminating the gold photocathode with light from a 2-W mercury vapor lamp which has 90% of its output at 2537 A. The resulting beam has an energy spread of 0.41 eV. Electron beam intensities of -10 7 electronslcm 2 s are produced with a 200 W medium pressure mercury arc lamp. For this case, the beam has a width in energy of 0.55 eV. Detectors to be calibrated are mounted within a set of computer-controlled rotational and translational tables. The tables allow the look direction of the detector to be oriented with respect to the beam in two orthogonal angles and two orthogonal directions. The entire calibration system operates within a set of Helmholtz coils that allow the Earth's magnetic field to be canceled. The voltage on the gold surface, the angular and spatial positioning of the detector, and the accumulation and display of the data are all controlled by a minicomputer.
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