Time‐of‐flight mass spectrographs—From ions to neutral atoms

Abstract

After their introduction to space physics in the mid 1980s time‐of‐flight (TOF) spectrographs have become a main staple in spaceborne mass spectrometry. They have largely replaced magnetic spectrometers, except when extremely high mass resolution is required to identify complex molecules, for example, in the vicinity of comets or in planetary atmospheres. In combination with electrostatic analyzers and often solid state detectors, TOF spectrographs have become key instruments to diagnose space plasma velocity distributions, mass, and ionic charge composition. With a variety of implementation schemes that also include isochronous electric field configurations, TOF spectrographs can respond to diverse science requirements. This includes a wide range in mass resolution to allow the separation of medium heavy isotopes or to simply provide distributions of the major species, such as H, He, and O, to obtain information on source tracers or mass fluxes. With a top‐hat analyzer at the front end, or in combination with deflectors for three‐axis stabilized spacecraft, the distribution function of ions can be obtained with good time resolution. Most recently, the reach of TOF ion mass spectrographs has been extended to include energetic neutral atoms. After selecting the arrival direction with mechanical collimation, followed by conversion to ions, adapted TOF sensors form a new branch of the spectrograph family tree. We review the requirements, challenges, and implementation schemes for ion and neutral atom spectrographs, including potential directions for the future, while largely avoiding overlap with complementary contributions in this special issue.

In Situ Observations of Interstellar Pickup Ions from 1 au to the Outer Heliosphere

“…The advent of TOF spectrographs that allow species determination in the suprathermal energy range and provide superior background and noise suppression due to their built-in coincidence measurement in space physics enabled the diagnostics of PUIs in various environments (Möbius et al. 2016a ; Wüest 1998 ). As mentioned in Sect.…”

In Situ Mass Spectrometers for Applications in Space

“…In the "top-hat" ESA design incoming ions are precisely scanned by energy into the TOF region from which the ion mass is determined. Ions are preaccelerated (Möbius et al, 2016) piercing a thin foil to emit a secondary electron corresponding to a start signal. A secondary electron is also emitted from a second surface corresponding to a stop signal.…”