Low Energy Ion Measurements Research Articles

Spacecraft potential effects on low-energy ion measurements to be made by probe B1 of Comet Interceptor

ABSTRACT Spacecraft charging causes notorious issues for low-energy plasma measurements. The charged particles are accelerated towards or repelled from the spacecraft surface, affecting both their energy and travel direction. The latter results in a distortion of the effective field of view (FOV) of the instrument making the measurements. The Comet Interceptor mission, planned to be launched in 2029, will make a flyby of a long-period or interstellar comet that ideally is dynamically new. The mission comprises one main spacecraft A, developed by the European Space Agency (ESA), and two sub-probes B1 and B2, developed by the Japan Aerospace Exploration Agency and ESA, respectively. The low-energy plasma measurements made by Comet Interceptor will likely be affected by the spacecraft potential in the case of low relative flyby velocities. On probe B1, the Cometary Ion Mass Spectrometer (CIMS) of the Plasma Suite is an ion mass spectrometer, capable of measuring ions with energies down to 10 eV/q. In this work, we use the Spacecraft Plasma Interaction Software to study the influence of the spacecraft potential on the low-energy ion measurements to be made by CIMS in the inner cometary magnetosphere. The results show that the effective FOV of CIMS is distorted at low energies when the flyby velocity is low. The distortion level is highly geometry dependent, and the largest distortions are caused by the magnetometer boom. Furthermore, the results show that cold ions with bulk velocities in the range 1–10 km s−1, flowing both radially away from and inward towards the nucleus, are detectable by the instrument considering the nominal observation geometry.

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.

BepiColombo Mio Observations of Low‐Energy Ions During the First Mercury Flyby: Initial Results

AbstractWe present initial results of low‐energy ion observations from BepiColombo's first Mercury flyby. Unprecedentedly high time resolution measurements of low energy ions at Mercury by BepiColombo Mio reveal rapid (a few seconds) and large (1–2 orders of magnitude) fluctuations of ion flux around the magnetopause and within the magnetosphere. Around the magnetic equator in the pre‐midnight magnetotail, Mio observed plasma sheet ions consistent with previous observations. In the midnight magnetotail near the closest approach, Mio observed the co‐existence of high‐energy (∼keV/q) and low‐energy (<∼300 eV/q) ion components. The low‐energy component is inferred to be cold with a temperature well below 100 eV and have a major contribution to the total density as opposed to previously reported cold tenuous ions. Future observations by Mio will provide insights into the sources, transport, and acceleration of the newly identified ion components.

Performance of a Low Energy Ion Source with Carbon Nanotube Electron Emitters under the Influence of Various Operating Gases.

Low energy ion measurements in the vicinity of a comet have provided us with important information about the planet’s evolution. The calibration of instruments for thermal ions in the laboratory plays a crucial role when analysing data from in-situ measurements in space. A new low energy ion source based on carbon nanotube electron emitters was developed for calibrating the ion-mode of mass spectrometers or other ion detectors. The electron field emission (FE) properties of carbon nanotubes (CNTs) for H2, He, Ar, O2, and CO2 gases were tested in the experiments. H2, He, Ar, and CO2 adsorbates could change the FE temporarily at pressures from10−6 Pa to10−4 Pa. The FE of CNT remains stable in Ar and increases in H2, but degrades in He, O2, and CO2. All gas adsorbates lead to temporary degradation after working for prolonged periods. The ion current of the ion source is measured by using a Faraday cup and the sensitivity is derived from this measurement. The ion currents for the different gases were around 10 pA (corresponding to 200 ions/cm3 s) and an energy of ~28 eV could be observed.

Cosmic Ray 11-Year Modulation for Sunspot Cycle 24

Galactic cosmic-ray (GCR) modulation at 1 AU for sunspot (SSN) Cycle 24 is studied using data from a global network of detectors and balloon measurements of low-energy ions at high latitudes in Russia. The observed modulation is modest compared with previous cycles. The tilt angle of the heliospheric current sheet reached a maximum value for Cycle 24 even though the peak of the interplanetary magnetic-field intensity at 1 AU has a much lower value (≈ 5 nT). The solar polar field in the northern hemisphere reversed in June 2012 and again in March 2014 while that in the southern hemisphere reversed in July 2013. The double field reversal in northern hemisphere after SSN maximum is not expected from dynamo theory. GCR modulation is at maximum phase in 2013. We have also studied the anomalous GCR recovery in 2009 using data from a low-energy proton channel on Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA). The rigidity dependence of the Cycle 24 modulation is computed using data from neutron monitors, directional muon telescopes at Nagoya, Japan, and detectors on balloons at high latitudes in Russia. It is a power law with an exponent −1.29, similar to previous solar cycles (−1.2±0.1); the nearly linear dependence of the modulation on the rigidity over a wide range poses a challenge to the quasi-linear theory (QLT) of GCR modulation.

Low Energy Charged Particle Measurement by MAP-PACE Onboard KAGUYA

MAP-PACE (MAgnetic field and Plasma experiment - Plasma energy Angle and Composition Experiment) is one of the scientific instruments onboard the KAGUYA (SELENE) satellite. PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measure the distribution function of low energy electrons below 15keV, while IMA and IEA measure the distribution function of mass identified low energy ions below 28keV/q. Since KAGUYA is a three-axis stabilized spacecraft, a pair of electron sensors (ESA-S1 and S2) and a pair of ion sensors (IMA and IEA) are necessary for obtaining three-dimensional distribution function of electrons and ions. Low energy ion measurements on the lunar orbit have been realized more than 30 years after the Apollo period. In addition, nobody has ever measured the mass identified three-dimensional distribution function of low energy ions at 100km altitude. PACE discovered surprisingly active low energy ion environment around the Moon. Instead of being absorbed by the lunar surface, quite a large amount of solar wind ions are reflected back from the Moon. The reflected solar wind ions are accelerated above solar wind energy picked up by the electric field in the solar wind.

Solar wind proton reflection at the lunar surface: Low energy ion measurement by MAP‐PACE onboard SELENE (KAGUYA)

Interaction between the solar wind and objects in the solar system varies largely according to the settings, such as the existence of a global intrinsic magnetic field and/or thick atmosphere. The Moon's case is characterized by the absence of both of them. Low energy ion measurements on the lunar orbit is realized more than 30 years after the Apollo period by low energy charged particle analyzers MAP‐PACE on board SELENE(KAGUYA). MAP‐PACE ion sensors have found that 0.1%∼1% of the solar wind protons are reflected back from the Moon instead of being absorbed by the lunar surface. Some of the reflected ions are accelerated above solar wind energy as they are picked‐up by the solar wind convection electric field. The proton reflection that we have newly discovered around the Moon should be a universal process that characterizes the environment of an airless body.

Jovian periodicities (∼10 h, ∼40 min) on Ulysses’ Distant Jupiter Encounter observations around the Halloween CIR events

We analyzed data from four different instruments (HI-SCALE, URAP, SWOOPS, VHM/FGM) onboard Ulysses spacecraft (s/c) and we searched for possible evidence of Jovian emissions when the s/c approached Jupiter during the times of Halloween events (closest time approach/position to Jupiter: February 5, 2004/ R = 1683 R J, θ = ∼49°). In particular, we analyzed extensively the low energy ion measurements obtained by the HI-SCALE experiment in order to examine whether low energy ion/electron emissions show a symmetry, and whether they are observed at north high latitudes upstream from the jovian bow shock, as is known to occur in the region upstream from the south bow shock as well ( Marhavilas et al., 2001). We studied the period from October 2003 to March 2004, as Ulysses moved at distances 0.8–1.2 AU from the planet at north Jovicentric latitudes <75°, and we present here an example of characteristic Jovian periodicities in the measurements around a CIR observed by Ulysses on days ∼348–349/2003 ( R = 1894 R J, θ = 72°). We show that Ulysses observed low energy ion (∼0.055–4.7 MeV) and electron (>∼40 keV) flux and/or spectral modulation with the Jupiter rotation period (∼10 h) as well as variations with the same period in solar wind parameters, radio and magnetic field directional data. In addition, characteristic strong ∼40 min periodic variations were found superimposed on the ∼10 h ion spectral modulation. Both the ∼10 h and ∼40 min ion periodicities in HI-SCALE measurements were present in several cases during the whole period examined (October 2003 to March 2004) and were found to be more evident during some special conditions, for instance during enhanced fluxes around the start (forward shock) and the end (reverse shock) of CIRs. We infer that the Jovian magnetosphere was triggered by the impact of the CIRs, after the Halloween events, and it was (a) a principal source of forward and reverse shock-associated ion flux structures and (b) the cause of generation of ∼10 h quasi-periodic magnetic field and plasma modulation observed by Ulysses at those times.

Improvement of plasma measurements onboard Cluster due to spacecraft potential control

The ion emitter experiment ASPOC (Active Spacecraft Potential Control) and the plasma electron experiment PEACE (Plasma Electron And Current Experiment) have been operating together in a large variety of plasma environments. Three cases on February 4, 2001, May 21, 2002, and June 12, 2002 have been analysed. A clear improvement of the electron measurements was found in regions with low plasma density in the lobes and the polar zones as well as near boundaries of these regions where the sustained spacecraft potential of less than ≈8 V helps to identify features in the electron spectra at low energy and facilitates the accurate calculation of moments. The variations of the electron distribution function were consistent with a change of the spacecraft potential from ≈40 to ≈8 V when ASPOC was turned on. A significant reduction of the count rates by photo-electrons generated at spacecraft surfaces was found. Also the low-energy ion measurements by the Cluster Ion Spectrometer improve using active spacecraft potential control. The refinement of the energy resolution of the electron detectors at low-energy levels is an important feature for accurate plasma measurements.

Electrostatic interaction between Interball-2 and the ambient plasma. 2. Influence on the low energy ion measurements with Hyperboloid

Abstract. The measurement of the thermal ion distributions in space is always strongly influenced by the ion motion through the complex 3D electrostatic potential structure built around a charged spacecraft. In this work, we study the related aberrations of the ion distribution detected on board, with special application to the case of the Hyperboloid instrument borne by the Interball-2 auroral satellite. Most of the time, the Interball-2 high altitude auroral satellite is charged at some non-negligible positive potential with respect to the ambient plasma, as shown in part 1; in consequence, the measurement of magnetospheric low energy ions (&lt; 80 eV) with the Hyperboloid instrument can be disturbed by the complex electric potential environment of the satellite. In the case of positive charging, as in previous experiments, a negative bias is applied to the Hyperboloid structure in order to reduce this effect and to keep as much as possible the opportunity to detect very low energy ions. Then, the ions reaching the Hyperboloid entrance windows would have travelled across a continuous huge electrostatic lens involving various spatial scales from ~ 10 cm (detector radius) to ~ 10 m (satellite antennas). Neglecting space charge effects, we have computed the ion trajectories that are able to reach the Hyperboloid windows within their acceptance angles. There are three main results: (i) for given values of the satellite potential, and for each direction of arrival (each window), we deduced the related energy cutoff; (ii) we found that all ions in the energy channel, including the cutoff, can come from a large range of directions in the unperturbed plasma, especially when the solar panels or antennas act as electrostatic mirrors; (iii) for higher energy channels, the disturbances are reduced to small angular shifts. Biasing of the aperture is not very effective with the Hyperboloid instrument (as on previous missions with instruments installed close to the spacecraft body) because the potential environment is driven by effects from the spacecraft. Our results are used to explain some unexpected features of the low energy ion measurements, especially during polar wind events recorded by Hyperboloid. In conclusion, knowing the satellite potential from IESP measurements, we were able to reject any low energy doubtful data and to perform angular corrections for all higher energy ion data. Then the selected and corrected data are a reliable basis for interpretation and estimation of the thermal ion distributions.Key words. Space plasma physics (charged particle motion and acceleration; numerical simulation studies; spacecraft sheaths, wakes, charging)

Low-energy ion measurements by means of CR-39 nuclear track detectors

The paper presents an additional acceleration system, used to shift up an ion energy spectrum by 20 keV , and some examples of the ion parabolas registered by means of a Thomson-type spectrometer within the rod plasma injector (RPI-60) facility, designed for plasma physics and application studies. The use of the described acceleration system and CR-39 track detectors has enabled the registration of ions of energy above 20 keV to be performed. It made possible to measure the ion (e.g. deuteron) energy spectrum more exactly in the low-energy range, what is important for the determination of ion emission characteristics.

GEOTAIL observations of electrostatic waves in the lower hyrid frequency range in the plasma sheet boundary layer

Quasi‐monochromatic waves with an electrostatic nature in the lower hybrid frequency range have been identified in the plasma sheet boundary layer at XGSM=−49Re and −69Re by the wave‐form observations in a band 0–25 Hz from the double probe onboard the GEOTAIL spacecraft. Simultaneous measurements of low energy ions also indicate that the wave coincides with the transition of the ion‐energy from 0.1 keV/e to 10 keV/e.

Energy loss measurements of low energy ions in thin carbon foils

The energy losses in thin carbon foils of ions of N, Ne, Ar, Mn, Kr and Xe have been measured at 100 keV and 200 keV using a high-resolution magnetic spectrometer, with a view to improving the accuracy of beam-foil lifetime measurements. For high- Z particles, the results show that a straightforward application of the Linhard-Scharff-Schiott total stopping cross-sections to beam-velocity correction can substantially overestimate the reduction in velocity due to the foil.

Use of an electrostatic particle guide for time-of-flight spectroscopy of low energy ions

It is shown that the electrostatic particle guide technique can be utilized in time-of-flight measurements of low-energy ions to establish long flight paths without severe loss of intensity. The system was tested using ions from an electron impact ion source which simulated the properties of recoils from decay processes such as β-delayed neutron emission. Transmission efficiencies of up to 30% have been observed for recoil energies ranging from 500–3000 eV, corresponding to enhancements of up to 5000 for a 1 m flight path.

Evidence for a solar wind origin of auroral ions from low-energy ion measurements

A rocket-borne ion spectrometer capable of separating and detecting H+, He+, and He++ with energies between 2 and 24 kev has been flown into an early-evening proton aurora from Fort Churchill, Canada. The measurements made with a Black Brant 4 at altitudes to 775 km enabled the positive-ion composition of the primary auroral precipitation to be determined above the masking effects of atmospheric interactions. The proton differential energy spectrum was found to peak at 8 kev with an intensity of 1.5×105 (cm2 sec ster kev)−1, which is orders of magnitude less than some previously obtained values between 2 and 10 kev. No statistically significant flux of He+ was observed. The He++ intensity at 15 kev was measured to be 7±3.5×103 (cm2 sec ster kev)−1 and an upper limit of 5×103 was set at 7.5 kev. The He++/H+ ratios determined from these data were combined with the two previously reported measurements at higher energies to obtain an auroral He++ differential energy spectrum. The H+ and He++ energy spectra were used to calculate an integrated He++/H+ flux ratio of approximately 4%. Some comments on characteristics of auroral particle acceleration mechanisms are presented. The observation of auroral He++ and H+ ions of approximately the same ratio as in the solar wind, and the apparent lack of He+ ions, is interpreted as strong evidence for a direct solar wind origin of the particles.