Light Ion Mass Spectrometer for space-plasma investigations

Abstract

Recent studies of the low-energy plasma population in the Earth’s space environment have revealed that this plasma population is much more complex than previously supposed and that a simple model of ionospheric evaporation cannot explain the distributions. There was a need to develop an advanced instrument to study this plasma in detail, and this paper describes the scientific background, design, development, and in-flight characteristics of such an instrument, the Light Ion Mass Spectrometer (LIMS). This instrument combines a magnetic mass spectrometer, a planar-grid retarding potential analyzer, and multidirectional sensor heads to measure the mass composition, density, temperature, and flow velocity of low-energy (E〈100 eV) plasma. The studies which were conducted leading to the final design will be discussed in detail and will illustrate certain effects which arose in the combining of energy and mass analysis into a single sensor. The instrument was flown on a high-altitude satellite in February 1979, and selected flight data will be presented to demonstrate the instrument performance.

Potential modulation on the SCATHA spacecraft

“…The antennas were slowly deployed starting in late February and ending in early March 1979. The NASA/Marshall light ion mass spectrometer (LIMS) is described in detail by Reasoner et al 8 A retarding potential analyzer was used in conjunction with a magnetic mass spectrometer to measure the total flux and energy distribution (for energies less than 100 eV) of H+ , He+ , and 0+. There are three sensors associated with this instrument.…”

Characteristics of low‐energy plasma in the plasmasphere and plasma trough

“…The LIMS/SCATHA instrument, however, combined a retarding potential analyzer (RPA) with a magnetic mass spectrometer in order that the detailed energy distribution of the low-energy plasma populations could be measured. The instrument is described in detail by Reasoner et al, [1982]. Here we point out only the relevant features of the LIMS.…”

“…Inherent in the design of the LIMS instrument are the effects that as the ion mass increases the energy passband over which a particular ion can be detected decreases. Furthermore, as the ion energy increases the solid angle response of the instrument decreases and this effect is much more pronounced for higher mass ions [Reasoner et al, 1982 ].…”

“…Furthermore, as the ion energy increases the solid angle response of the instrument decreases and this effect is much more pronounced for higher mass ions[Reasoner et al, 1982 ].The decrease of the solid angle response is the worst of the two effects for limiting the flux into the instrument. Rather the whole local time region in which the encounters Example of a warm field-aligned plasma.…”

Integrated development facility for the calibration of low-energy charged particle flight instrumentation

“…Direct measurements are made of the beam energy and composition with a retarding energy analyzer and an ion mass spectrometer (IMS) located near the plane of the instrument entrance aperture. This system, and its predecessors, has been used to calibrate and develop such instruments as the Light Ion Mass Spectrometer (LIMS) [10] and the Retarding Ion Mass Spectrometer (RIMS) [4], and is currently being used to develop the Thermal Ion Dynamics Experiment for the International Solar Terrestrial Program. Table 1 shows the typical range of parameters covered by this facility.…”