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Many space plasmas (especially electrons generated in planetary ionospheres) exhibit fine-detailed structures that are challenging to fully resolve with the energy resolution of typical space plasma analyzers (10% → 20%). While analyzers with higher resolution have flown, generally this comes at the expense of sensitivity and temporal resolution. We present a new technique for measuring plasmas with extremely high energy resolution through the combination of a top-hat Electrostatic Analyzer (ESA) followed by an internally mounted Retarding Potential Analyzer (RPA). When high resolutions are not required, the RPA is grounded, and the instrument may operate as a typical general-purpose plasma analyzer using its ESA alone. We also describe how such an instrument may use its RPA to remotely vary the geometric factor (sensitivity) of a top hat analyzer, as was performed on the New Horizons Solar Wind at Pluto and MAVEN SupraThermal and Thermal Ion Composition instruments. Finally, we present results from laboratory testing of our prototype, showing that this technique may be used to construct an instrument with 1.6% energy resolution, constant over all energies and angles. [ABSTRACT FROM AUTHOR]

The stability of a thin current sheet with a finite guide field is investigated in the weak guide-field limit by means of linear theory and simulation. The emphasis is placed on the lower-hybrid drift instability (LHDI) propagating along the current flow direction. Linear theory is compared against the two-dimensional linear simulation based on the gyrokinetic electron/fully kinetic ion code. LHDI is a flute mode characterized by k·Btotal=0; hence, it is stabilized by a finite guide field if one is confined to k vector strictly parallel to the cross-field current. Comparison of the theory and simulation shows qualitatively good agreement. [ABSTRACT FROM AUTHOR]

Low-energy plasmas having temperatures of order 1 eV or less are found commonly in the ionospheres and space environments of Earth and other planets. Measuring the density, temperature, drift velocities, phase-space anisotropies, and other properties of these plasmas presents numerous challenges. Examples are distortions of particle trajectories due to spacecraft wakes, spacecraft charging, and particle gyromotion in magnetized plasmas. Furthermore, these plasmas are known to organize into structures as small as tens of meters across, traversed by spacecraft in tens of milliseconds or less. The Suprathermal Plasma Imager (SPI) was developed to address these challenges. The SPI is optimized for measurements of particles with ∼1 eV energies, and of the suprathermal extension of those populations up to several hundred eV. The SPI is sensitive to particle flux intensities of order 6×10[SUP5] cm[SUP-2] s[SUP-1] sr[SUP-1] eV[SUP-1] and greater. It produces 3024-pixel images corresponding to two-dimensional (angle/energy) cuts through plasma velocity distribution functions, with an image frame rate of up to 100 s[SUP-1]. The SPI has a cylindrical sensor head measuring 37.5 mm in diameter and 14 cm long, with a mass of 350 g. The relatively small size and mass of the sensor allow it to be deployed easily on a boom, outside of the spacecraft's electrical sheath and in a region where wake perturbations are reduced. The SPI sensor head contains no electronic circuitry, but instead creates a visible image of the particle distribution with a system of dc-biased grids, microchannel plates, and a phosphor screen. The phosphor image is transferred via an imaging fiber-optic cable to an instrument box in the main spacecraft body, where it is sampled with a charge-coupled device and support electronics. Inside the sensor, angle/energy images of incident particle distributions are formed by a pair of concentric hemispherical grids. The incident energies E[SUBi]... [ABSTRACT FROM AUTHOR]