Holistic numerical calibration of the iMESA electrostatic analyzer.

A drifted Maxwellian velocity distribution is the most common model used to interpret the data from low-energy charged-particle instruments onboard spacecraft that are used to investigate the ambient plasma environment in the low Earth orbit (LEO). An original method is presented for determining the flow parameters (density, temperature, and flow energy) of such a distribution from the output of the integrated miniaturized electrostatic analyzer, which has been successfully flown on several LEO missions. Rather than attempting to deconvolve from the on-orbit data the analyzer's response to an ideal, monoenergetic input, numerical simulation is used to predict and parameterize the response of the device to an input distribution that includes an isotropic, non-zero temperature, yielding a straightforward method for extracting the flow parameters from the spacecraft data. The method is computationally simple enough to be incorporated into a robust algorithm suitable for rapid batch processing or real-time analysis of data.

The integrated miniaturized electrostatic analyzer: A space plasma environment sensor.

The integrated Miniaturized Electrostatic Analyzer (iMESA) was a satellite-based ionospheric sensor that operated on NASA's Space Test Program Satellite (STPSat-3) from December 2013 to July 2019. The instrument's scientific objective was to (1) measure the plasma density in low Earth orbit, (2) measure the plasma temperature in low Earth orbit, and (3) quantify the spacecraft potential with respect to the ambient plasma potential in the ionosphere. iMESA sampled the ionosphere every 10 s by measuring the ion current density through the ESA as a result of the motion of the spacecraft through the plasma. Current density spectra were transmitted to the ground where they were post-processed into ion density spectra and then analyzed numerically to determine the ion density, ion temperature, and spacecraft potential. This article discusses the instrument design and simulation, the determination of a geometric factor, and data processing procedures and evaluates the final data product with regard to the mission success criteria. The ion density and ion temperature captured by the iMESA instrument are on the same order and range as the values predicted in the literature. The spacecraft potential was also quantified. The conclusion after the evaluation of the instrument's data product is that the scientific mission is successful on all three points.

On the Emergence Mechanism of Carrot Sprites.

We investigate the launch of negative upward streamers from sprite glows. This phenomenon is readily observed in high-speed observations of sprites and underlies the classification of sprites into carrot or column types. First, we describe how an attachment instability leads to a sharply defined region in the upper part of the streamer channel. This region has an enhanced electric field, low conductivity and strongly emits in the first positive system of molecular nitrogen. We identify it as the sprite glow. We then show how, in the most common configuration of a carrot sprite, several upward streamers emerge close to the lower boundary of the glow, where negative charge gets trapped and the lateral electric field is high enough. These streamers cut off the current flowing toward the glow and lead to the optical deactivation of the glow above. Finally, we discuss how our results naturally explain angel sprites.

A laminated energetic electrostatic analyzer for 0-5 keV charged particles.

A compact electrostatic energy bandpass filter based on a laminated analyzer design has been developed to measure charged particle fluxes at energies ranging from 0 to 5 keV. The sensor head has been successfully tested against a low energy magnetically filtered plasma source and an ion beam source capable of producing energetic ions in the range of 100-1250 eV. Additionally, the instrument has demonstrated the ability to accurately measure negative spacecraft frame charging using a low Earth orbit plasma simulator. The effects of the spacecraft frame charging on the measured energy distribution measurements and the impact regarding the derived charged particle density and temperature parameters are also examined.

Screens versus microarrays for ruggedized retarding potential analyzers.

An array of highly miniaturized electrostatic lenses is shown to be a viable replacement for meshes or screens in a retarding potential analyzer (RPA) where mechanical ruggedness or the ability to intercept large currents of energetic particles is desirable. Data from a prototype device are presented cross-calibrated with a traditional planar RPA indicating how the so-called microarray configuration avoids energy-dependent transparency (either reduced or enhanced) associated with meshes or screens while providing accurate energy analysis with reasonable energy resolution. In contrast, another ruggedized configuration employing a screen is presented, showing the severity of energy-dependent enhanced transparency, verified by numerical simulation.