Top-hat Electrostatic Analyzer Research Articles

A low-energy particle experiment for both ion and electron measurements using a single microchannel plate-based detector

We have developed a low-energy particle experiment that alternately measures ions and electrons in space. The ability to switch between ion and electron measurements is achieved by simply adding ultra-thin carbon foils and positive and negative outputs to a conventional top-hat electrostatic analyzer and a high-voltage power supply, respectively. The advantage of this experiment is that it can perform both ion and electron measurements using only one MCP-based detector for electrons, since it detects secondary electrons emitted from the carbon foils. For the SS520-3 sounding rocket program, we prepared two identical energy analyzers, one for ions and the other for electrons to demonstrate this technique. Laboratory tests confirmed that the performance of the two analyzers was comparable to that of conventional analyzers for ion and electrons. The SS520-3 rocket experiment in the high latitude auroral region yielded observations that captured typical features of ions and electrons, which were similar to previous observations.Graphical

A gated-time-of-flight top-hat electrostatic analyzer for low energy ion measurements

When incorporated into a top-hat electrostatic analyzer, a gate electrode enables the separation of ions by their mass-per-charge with modest mass resolution (M/∆M ∼ 10). Gated-time-of-flight (TOF) instruments avoid the energy straggling and angular scattering effects prevalent in foil-based detection systems, providing more pristine measurements of three-dimensional distribution functions of incident ions. Gated-TOF implementations are ideal for measuring the properties of low-energy (i.e., <100 eV) thermal ions in various space environments. We present an instrument prototype capable of separating H+, He+, O+, and O2+ in Earth’s ionosphere and demonstrate that in addition to providing species determination, precise operation of the gate electrode provides an electronically adjustable geometric factor that can extend a single instrument’s dynamic range by several orders of magnitude.

A low-energy ion spectrometer with large field of view and wide energy range onboard a Chinese GEO satellite

Abstract A low-energy ion spectrometer (LEIS), onboard a Chinese navigation satellite in geosynchronous orbit, is one of the primary instruments for plasma detection. The LEIS is implemented by combining a top-hat electrostatic analyzer with a pair of angular scanning deflectors, which enables us to achieve in situ measurement of energetic ions in three-dimensional (3D) space with a large field of view of 360° × 90° and a wide energy range from 50 eV to 25 keV per charge. The key performance parameters including analyzer constant, geometric factor, linear relation function between elevation angles and deflector voltages, and the energy or angular resolutions have been determined by using detailed simulations and calibration experiments on the ground. The preliminary results from on-orbit observations demonstrate that the capability of the present LEIS payload can well meet the mission requirements for sampling the low-energy ion distributions in 3D space, measuring the negative satellite surface potential, and monitoring the magnetospheric storm or substorm activities.

Effects of noise on the accuracy of plasma bulk parameters derived from velocity moments of in-situ observations

We expose and quantify the inaccuracies of plasma bulk parameters derived from the calculation of velocity moments of noisy in-situ plasma observations. First, we simulate typical solar wind proton plasma observations, obtained by a typical top-hat electrostatic analyzer instrument. We add background noise to the simulated observations and analyze them by applying standard methods to derive the plasma density, speed, and temperature. We then compare the analysis results with the parameters we use to simulate the observations in the first place, in order to quantify the inaccuracies in the calculated plasma parameters as functions of the noise level in the observations. We find that even noise levels that are smaller than 1% of the signal peak, lead to significant inaccuracies in some plasma parameters. The plasma temperature suffers the biggest inaccuracies and the plasma speed the smallest. Our results highlight the importance of removing noise from observations when calculating the moments of the constructed plasma distributions. We finally, evaluate one simple method to remove uniform background noise automatically from measurements, which is useful for future on-board analyses.

Evaluating the Performance of a Plasma Analyzer for a Space Weather Monitor Mission Concept

AbstractWe use historical analysis of solar wind plasma and coronal mass ejections to define the range of performance required for an ion analyzer for future space weather monitoring missions. We adopt the design of a top hat electrostatic analyzer, capable of measuring the plasma protons and constructing their three‐dimensional distribution functions. The design is based on previous heritage instruments and allows monitoring of extreme space weather events. In order to evaluate the future observations and their analysis methods, we model the expected response of the instrument in simulated plasma conditions. We evaluate a novel analysis method which can determine on board the plasma bulk properties, such as density, velocity, and temperature from the statistical moments of the observed velocity distribution functions of the plasma particles. We quantify the accuracy of the derived parameters critical for space weather purposes, by comparing them with the corresponding input solar wind parameters. In order to validate the instrument design, we examine the accuracy over the entire range of the input parameters we expect to observe in solar wind, from benign to extreme space weather conditions. We also use realistic parameters of fast solar wind streams and interplanetary coronal mass ejections as measured by the Advanced Composition Explorer spacecraft, to investigate the performance of the example instrument and the accuracy of the analysis. We discuss the achieved accuracy and its relevance to space weather monitoring concepts. We address sources of significant errors, and we demonstrate potential improvements by using a fitting analysis method to derive the results.

Statistical Uncertainties of Space Plasma Properties Described by Kappa Distributions.

The velocities of space plasma particles often follow kappa distribution functions, which have characteristic high energy tails. The tails of these distributions are associated with low particle flux and, therefore, it is challenging to precisely resolve them in plasma measurements. On the other hand, the accurate determination of kappa distribution functions within a broad range of energies is crucial for the understanding of physical mechanisms. Standard analyses of the plasma observations determine the plasma bulk parameters from the statistical moments of the underlined distribution. It is important, however, to also quantify the uncertainties of the derived plasma bulk parameters, which determine the confidence level of scientific conclusions. We investigate the determination of the plasma bulk parameters from observations by an ideal electrostatic analyzer. We derive simple formulas to estimate the statistical uncertainties of the calculated bulk parameters. We then use the forward modelling method to simulate plasma observations by a typical top-hat electrostatic analyzer. We analyze the simulated observations in order to derive the plasma bulk parameters and their uncertainties. Our simulations validate our simplified formulas. We further examine the statistical errors of the plasma bulk parameters for several shapes of the plasma velocity distribution function.

Mars Ion and Neutral Particle Analyzer (MINPA) for Chinese Mars Exploration Mission (Tianwen-1): Design and ground calibration

The main objective of the Mars Ion and Neutral Particle Analyzer (MINPA) aboard the Chinese Mars Exploration Mission (Tianwen-1) is to study the solar wind–Mars interaction by measuring the ions and energetic neutral atoms (ENAs) near Mars. The MINPA integrates ion and ENA measurements into one sensor head, sharing the same electronics box. The MINPA utilizes a standard toroidal top-hat electrostatic analyzer (ESA) followed by a time of flight (TOF) unit to provide measurement of ions with energies from 2.8 eV to 25.9 keV and ENAs from 50 eV to 3 keV with a base time resolution of 4 seconds. Highly polished silicon single crystal substrates with an Al2O3 film coating are used to ionize the ENAs into positive ions. These ions can then be analyzed by the ESA and TOF, to determine the energy and masses of the ENAs. The MINPA provides a 360°×90° field of view (FOV) with 22.5°×5.4° angular resolution for ion measurement, and a 360°×9.7° FOV with 22.5°×9.7° angular resolution for ENA measurement. The TOF unit combines a –15 kV acceleration high voltage with ultra-thin carbon foils to resolve H+, He2+, He+, O+, O2+ and CO2+ for ion measurement and to resolve H and O (≥ 16 amu group) for ENA measurement. Here we present the design principle and describe our ground calibration of the MINPA.

The analyzer constant of top hat electrostatic analyzer: comparison between theory and simulations

The top hat electrostatic analyzer is widely used to measure ion and electron fluxes variation in the relatively small region of space. The goal of this investigation is to report our findings about the difference of the analyzer constant K determined by two methods that are respectively the theory (Kthe) and simulation (Ksim). Firstly, an analyzer is designed with the radius R1 = 30 mm and the gap d = 2 mm, and the performance parameters of analyzer are obtained, including the analyzer constant K, energy resolution Δ E/Ek, and pixel geometric factor GF through the theory model and simulation. Since the analyzer constant K can be obtained both from theory (Kthe) and simulation (Ksim), a difference between the two has been obtained and, in particular, Kthe has resulted greater than Ksim. Analyzing the structure of top hat electrostatic analyzer, we drew as a conclusion that the non-uniform electrostatic field in the region of top hat accelerates the incident ions and generates the difference for the analyzer constant K. To analysis and take into account the difference between Kthe and Ksim, a function f(R0/d), which depends on the design parameters, are derived from the simulated results.

A hybrid electrostatic retarding potential analyzer for the measurement of plasmas at extremely high energy resolution.

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.

A low-energy ion spectrometer with half-space entrance for three-axis stabilized spacecraft

A low-energy ion spectrometer (LEIS) for use aboard three-axis stabilized spacecraft has been developed to measure ion energy per charge distribution in three-dimensional space with good energy-, angular- and temporal-resolutions. For the standard top-hat electrostatic analyzer used widely in space plasma detection, three-axis stabilized spacecraft makes it difficult to obtain complete coverage of all possible ion arrival directions. We have designed angular scanning deflectors supplementing to a cylindrically symmetric top-hat electrostatic analyzer to provide a half-space field of view as 360°×90° (–45°–+45°), and fabricated the LEIS flight model for detecting magnetospheric ions in geosynchronous orbit. The performance of this payload has been evaluated in detail by a series of simulation and environmental tests, and the payload has also been calibrated through laboratory experiments using a low-energy ion source. The results show that capabilities of the LEIS payload are in accordance with the requirements of a magnetospheric mission.

Low-energy particle experiments\u2013electron analyzer (LEPe) onboard the Arase spacecraft

In this report, we describe the low-energy electron instrument LEPe (low-energy particle experiments–electron analyzer) onboard the Arase (ERG) spacecraft. The instrument measures a three-dimensional distribution function of electrons with energies of sim 19 eV–19 keV. Electrons in this energy range dominate in the inner magnetosphere, and measurement of such electrons is important in terms of understanding the magnetospheric dynamics and wave–particle interaction. The instrument employs a toroidal tophat electrostatic energy analyzer with a passive 6-mm aluminum shield. To minimize background radiation effects, the analyzer has a background channel, which monitors counts produced by background radiation. Background counts are then subtracted from measured counts. Electronic components are radiation tolerant, and 5-mm-thick shielding of the electronics housing ensures that the total dose is less than 100 kRad for the one-year nominal mission lifetime. The first in-space measurement test was done on February 12, 2017, showing that the instrument functions well. On February 27, the first all-instrument run test was done, and the LEPe instrument measured an energy dispersion event probably related to a substorm injection occurring immediately before the instrument turn-on. These initial results indicate that the instrument works fine in space, and the measurement performance is good for science purposes.

Electrostatic analyzer measurements of ionospheric thermal ion populations

AbstractWe define the observational parameter regime necessary for observing low‐altitude ionospheric origins of high‐latitude ion upflow/outflow. We present measurement challenges and identify a new analysis technique which mitigates these impediments. To probe the initiation of auroral ion upflow, it is necessary to examine the thermal ion population at 200–350 km, where typical thermal energies are tenths of eV. Interpretation of the thermal ion distribution function measurement requires removal of payload sheath and ram effects. We use a 3‐D Maxwellian model to quantify how observed ionospheric parameters such as density, temperature, and flows affect in situ measurements of the thermal ion distribution function. We define the viable acceptance window of a typical top hat electrostatic analyzer in this regime and show that the instrument's energy resolution prohibits it from directly observing the shape of the particle spectra. To extract detailed information about measured particle population, we define two intermediate parameters from the measured distribution function, then use a Maxwellian model to replicate possible measured parameters for comparison to the data. Liouville's theorem and the thin‐sheath approximation allow us to couple the measured and modeled intermediate parameters such that measurements inside the sheath provide information about plasma outside the sheath. We apply this technique to sounding rocket data to show that careful windowing of the data and Maxwellian models allows for extraction of the best choice of geophysical parameters. More widespread use of this analysis technique will help our community expand its observational database of the seed regions of ionospheric outflows.

In-flight performance and preliminary observational results of Solar Wind Ion Detectors (SWIDs) on Chang’E-1

SWIDs (Solar Wind Ion Detectors, SWID-A and SWID-B) are two of the scientific instruments on Chang’E-1, the first Chinese lunar mission. SWIDs utilize top-hat electrostatic analyzer to measure the low energy (<20keV/q) ion distribution of solar wind and the plasma environment around the Moon. SWIDs consist of two identical instruments with two perpendicular fan shaped field-of-views of 180°×6°. The preliminary observational results of SWIDs show that SWIDs were sufficient to measure the basic characteristics of the Moon-plasma interaction. A typical event about the Moon and solar wind interaction is discussed in this paper. Another new observational result near the Moon reported in this paper is the double proton beams coupled with a single alpha beam in solar wind. This is the first double ion beams event reported near the Moon. The double ion beams appeared having relatively anisotropic characteristics due to the interaction between solar wind and the Moon.

On variable geometric factor systems for top-hat electrostatic space plasma analyzers

Even in the relatively small region of space that is the Earth's magnetosphere, ion and electron fluxes can vary by several orders of magnitude. Top-hat electrostatic analyzers currently do not possess the dynamic range required to sample plasma under all conditions. The purpose of this study was to compare, through computer simulation, three new electrostatic methods that would allow the sensitivity of a sensor to be varied through control of its geometric factor (GF) (much like an aperture on a camera). The methods studied were inner filter plates, split hemispherical analyzer (SHA) and top-cap electrode. This is the first discussion of the filter plate concept and also the first study where all three systems are studied within a common analyzer design, so that their relative merits could be fairly compared. Filter plates were found to have the important advantage that they facilitate the reduction in instrument sensitivity whilst keeping all other instrument parameters constant. However, it was discovered that filter plates have numerous disadvantages that make such a system impracticable for a top-hat electrostatic analyzer. It was found that both the top-cap electrode and SHA are promising variable geometric factor system (VGFS) concepts for implementation into a top-hat electrostatic analyzer, each with distinct advantages over the other.

Mercury Ion Analyzer (MIA) onboard Mercury Magnetospheric Orbiter: MMO

The Mercury Magnetopsheric Orbiter (MMO) is one of the spacecraft of the BepiColombo mission; the mission is scheduled for launch in 2014 and plans to revisit Mercury with modern instrumentation. MMO is to elucidate the detailed plasma structure and dynamics around Mercury, one of the least-explored planets in our solar system. The Mercury Plasma Particle Experiment (MPPE) on board MMO is a comprehensive instrument package for plasma, high-energy particle, and energetic neutral particle atom measurements. The Mercury Ion Analyzer (MIA) is one of the plasma instruments of MPPE, and measures the three dimensional velocity distribution of low-energy ions (from 5 eV to 30 keV) by using a top-hat electrostatic analyzer for half a spin period (2 s). By combining both the mechanical and electrical sensitivity controls, MIA has a wide dynamic range of count rates for the proton flux expected around Mercury, which ranges from 10 6 to 10 12 cm −2 s −1 str −1 keV −1, in the solar wind between 0.3 and 0.47 AU from the sun, and in both the hot and cold plasma sheet of Mercury’s magnetosphere. The geometrical factor of MIA is variable, ranging from 1.0 × 10 −7 cm 2 str keV/keV for large fluxes of solar wind ions to 4.7 × 10 −4 cm 2 str keV/keV for small fluxes of magnetospheric ions. The entrance grid used for the mechanical sensitivity control of incident ions also work to significantly reduce the contamination of solar UV radiation, whose intensity is about 10 times larger than that around Earth’s orbit.

The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) for the Mars Express Mission

The general scientific objective of the ASPERA-3 experiment is to study the solar wind – atmosphere interaction and to characterize the plasma and neutral gas environment with within the space near Mars through the use of energetic neutral atom (ENA) imaging and measuring local ion and electron plasma. The ASPERA-3 instrument comprises four sensors: two ENA sensors, one electron spectrometer, and one ion spectrometer. The Neutral Particle Imager (NPI) provides measurements of the integral ENA flux (0.1–60 keV) with no mass and energy resolution, but high angular resolution. The measurement principle is based on registering products (secondary ions, sputtered neutrals, reflected neutrals) of the ENA interaction with a graphite-coated surface. The Neutral Particle Detector (NPD) provides measurements of the ENA flux, resolving velocity (the hydrogen energy range is 0.1–10 keV) and mass (H and O) with a coarse angular resolution. The measurement principle is based on the surface reflection technique. The Electron Spectrometer (ELS) is a standard top-hat electrostatic analyzer in a very compact design which covers the energy range 0.01–20 keV. These three sensors are located on a scanning platform which provides scanning through 180∘ of rotation. The instrument also contains an ion mass analyzer (IMA). Mechanically IMA is a separate unit connected by a cable to the ASPERA-3 main unit. IMA provides ion measurements in the energy range 0.01–36 keV/charge for the main ion components H+, He++, He+, O+, and the group of molecular ions 20–80 amu/q. ASPERA-3 also includes its own DC/DC converters and digital processing unit (DPU).

The Time-of-Flight Energy, Angle, Mass Spectrograph (Teams) Experiment for Fast

The Time-of-flight Energy Angle Mass Spectrograph (TEAMS) is being flown on the FAST Small Explorer mission to measure the 3-dimensional distribution function of the major ion species present in the lower magnetosphere. The instrument is similar to time-of-flight plasma analyzer systems that have been designed and planned for flight as CODIF (Composition and Distribution Function analyzer) on the four European Space Agency Cluster-II spacecraft and, as ESIC (Equator-S Ion Composition instrument) on Equator-S. This instrument allows the 3-dimensional distribution functions of individual ion species to be determined within 1/2 spin period (2.5 s). Two-dimensional distributions are measured in 80 ms. These capabilities are crucial for the study of selective energization processes in the auroral regions of the magnetosphere. The design, operational characteristics, and test and calibration results for this instrument are presented. The sensor consists of a toroidal top-hat electrostatic analyzer with instantaneous acceptance of ions over 360° in polar angle. After post-acceleration of the incoming ions by up to 25 kV, a time-of-flight mass spectrograph discriminates the individual species. It has been demonstrated through calibration that the instrument can easily separate H+, He2+, He+, O+ and, for energies after post-acceleration of > 20 keV, even O 2 + molecules. On-board mass discrimination and the internal accumulation of several distinct data quantities combined with the spacecraft’s flexible telemetry formatting allow for instrument data rates from 7.8 kb s−1 to 315 kb s−1 to be telemetered to ground through the FAST centralized Instrument Data Processor.

Instrumental characteristics of the Electron Spectrum Analyzer (ESA) onboard the Planet-B mission and observational perspectives of the electron measurements

An Electron Spectrum Analyzer (ESA) onboard the Planet-B mission to the planet Mars will measure the electron energy flux in the range of 12 eV to 15 keV in 32 energy steps. The sensor is essentially a toroidal top-hat electrostatic analyzer mounted on the surface of the spacecraft, which has a spin period of nominally 8 sec. With a 4° × 180° view angle and its spinal motion, the sensor can measure three-dimensional electron velocity distribution functions. Such distribution functions will be taken mostly during the perigee path with a high bit rate burst mode. In a nominal low bit rate mode, the reduced distribution data in the pitch-angle and energy phase space will be recorded and transmitted to Earth together with the burst mode data. This electron measurement will provide significant information for studies on the structure of the magnetosphere and ionosphere as well as information on particle acceleration and the wave-particle interaction processes around Mars.

Design, construction, and laboratory calibration of the Angle Resolving Energy Analyzer (AREA): a 'top-hat' instrument for auroral research

The design philosophy, construction, and laboratory evaluation of the AREA instrument for space plasma measurement, that is generically a top-hat electrostatic analyzer, are reported. The instrument accepts particles from eleven 16 degrees azimuth sectors equally spaced around 360 degrees in the acceptance plane. Laboratory measurements of energy resolution and angular responses demonstrate sharp focusing in azimuth, satisfactory energy resolution, and a large geometric factor. These measurements compare favorably with computer simulations of the same instrument reported previously.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>