Field structure and electron life times in the MEFISTO Electron Cyclotron Resonance Ion Source

The complex magnetic field of the permanent-magnet electron cyclotron resonance (ECR) ion source MEFISTO located at the University of Bern have been numerically simulated. For the first time the magnetized volume qualified for electron cyclotron resonance at 2.45 GHz and 87.5 mT has been analyzed in highly detailed 3D simulations with unprecedented resolution. New results were obtained from the numerical simulation of 25211 electron trajectories. The evident characteristic ion sputtering trident of hexapole confined ECR sources has been identified with the field and electron trajectory distribution. Furthermore, unexpected long electron trajectory lifetimes were found.Comment: 11 pages, 18 figure

Calibrating beam fluxes of a low-energy neutral atom beam facility.

Scientific detection and imaging instruments for low-energetic neutral atoms (ENA) onboard spacecraft require thorough pre-flight laboratory calibration against a well-characterized neutral atom beam source. To achieve this requirement, a dedicated test facility is available at the University of Bern, which is equipped with a powerful plasma ion source and an ion beam neutralization stage. Using surface neutralization, low-energy neutral atom beams of any desired gas species can be produced in the energy range from 3 keV down as low as 10 eV. As the efficiency of the neutralization stage is species and energy dependent, the neutralizer itself needs to be calibrated against an independent reference. We report on the calibration and characterization of this neutral atom beam source using our recently developed Absolute Beam Monitor (ABM) as a primary calibration standard. The ABM measures the absolute ENA flux independent of neutral species in the energy range from 10 eV to 3 keV. We obtain calibration factors of a few 100 cm-2 s-1 pA-1, depending on species at beam energies above about 100 eV, and a power-law decrease for energies below 100 eV. Furthermore, the energy loss of neutralized ions in the surface neutralizer is estimated from time-of-flight measurements using the ABM. The relative energy loss increases with ENA energy from low levels near zero up to 20%-35% at 3 keV, depending on atomic species. Having calibrated our neutral beam source allows for accurate calibration of ENA space instruments

Absolute beam monitor: A novel laboratory device for neutral beam calibration.

Instruments recording Energetic Neutral Atoms (ENAs) for space applications require thorough laboratory calibration in a dedicated test facility providing a neutral atom beam. Accurate knowledge of the neutral beam intensity and energy is central for the laboratory calibration procedure. However, until recently, the quantification of the neutral atom beam intensity in the low-energy range below a few 100 eV was based on relative measurements with standard detectors of approximately known detection efficiencies for neutral atoms. We report on the design and development of a novel calibration device dedicated to determining the ENA beam flux in an absolute manner in the energy range from 3 keV down to about 10 eV. This is realized by applying ENA scattering at a surface and coincident detection of scattered particles and created secondary electrons. Moreover, the neutral beam energy is determined by a time-of-flight measurement. The applied measurement principle relies on very low background signals. The observed background count rates are in the range 10-2 s for the individual channels and about 10-5 s for coincidence events. The background is, thus, at least two, typically four, orders of magnitude lower than the signal rate for neutral atom beams in the foreseen energy range. We demonstrate a concrete application using the absolute flux calibration of a laboratory neutralization stage

CubeSatTOF: Planetary Atmospheres Analyzed with a 1U High-Performance Time-Of-Flight Mass Spectrometer

This paper presents design and performance of a miniature time-of-flight mass spectrometer of 1U size for a CubeSat platform for quantitative chemical composition analysis of thin atmospheres. The atmospheres of solar system bodies harbor key information to answer questions about its origin and evolution, night-side transport, satellite drag including seasonal variation of it, chemical sputtering of satellites, and even the feasibility of earthquake forecast system has been suggested. Highly sensitive chemical analyses with our mass spectrometer will allow to obtain insight into atmospheric processes. We designed a compact multipurpose instrument. Its applicationis discussed for two mission concepts, namely orbiting Earth in a terrestrial swarm configuration or descending through the atmosphere of a planetary object during a flyby. Our measurements demonstrate that the instrument has mass range of about m/z 1 – 300 and a mass resolution so that the heavy noble gases such as krypton and xenon can be quantified in situ. Thanks to its ion optical performance, the CubeSatTOF instrument serves as a baseline technology for future analysis of both the terrestrial and extraterrestrial exospheres

Identification of the ECR zone in the SWISSCASE ECR ion source

The magnetic field of the permanent magnet electron cyclotron resonance (ECR) ion source SWISSCASE located at the University of Bern has been numerically simulated and experimentally investigated. For the first time the magnetized volume qualified for electron cyclotron resonance at 10.88 GHz and 388.6 mT has been analyzed in highly detailed 3D simulations with unprecedented resolution. The observed pattern of carbon coatings on the source correlates strongly with the electron and ion distribution in the ECR plasma of SWISSCASE. Under certain plasma conditions the ion distribution is tightly bound to the electron distribution and can considerably simplify the numerical calculations in ECR related applications such as ECR ion engines and ECR ion implanters.Comment: 9 pages, 8 figure

Advances in Mass Spectrometers for Flyby Space Missions for the Analysis of Biosignatures and Other Complex Molecules

Spacecraft flybys provide access to the chemical composition of the gaseous envelope of the planetary object. Typical relative encounter velocities range from km/s to tens of km/s in flybys. For speeds exceeding about 5 km/s, modern mass spectrometers analyzing the rapidly encountering gas suffer from intrinsic hypervelocity impact-induced fragmentation processes causing ambiguous results when analyzing complex molecules. In this case, instruments use an antechamber, inside which the incoming species collide many times with the chamber wall. These collisions cause the desired deceleration and thermalization of the gas molecules. However, these collisions also dissociate molecular bonds, thus fragmenting the molecules, and possibly forming new ones precluding scientists from inferring the actual chemical composition of the sampled gas. We developed a novel time-of-flight mass spectrometer that handles relative encounter velocities of up to 20 km/s omitting an antechamber and its related fragmentation. It analyzes the complete mass range of m/z 1 to 1000 at an instance. This innovation leads to unambiguous analysis of complex (organic) molecules. Applied to Enceladus, Europa or Io, it will provide reliable chemical composition datasets for exploration of the Solar System to determine its status, origin and evolution

Characteristics of proton velocity distribution functions in the near-lunar wake from Chandrayaan-1/SWIM observations

Due to the high absorption of solar wind plasma on the lunar dayside, a large scale wake structure is formed downstream of the Moon. However, recent in-situ observations have revealed the presence of protons in the near-lunar wake (100 km to 200 km from the surface). The solar wind, either directly or after interaction with the lunar surface (including magnetic anomalies), is the source of these protons in the near-wake region. Using the entire data from the SWIM sensor of the SARA experiment onboard Chandrayaan-1, we analysed the velocity distribution of the protons observed in the near-lunar wake. The average velocity distribution functions, computed in the solar wind rest frame, were further separated based on the angle between the upstream solar wind velocity and the IMF. Several proton populations were identified from the velocity distribution and their possible entry mechanism were inferred based on the characteristics of the velocity distribution. These entry mechanisms include (i) diffusion of solar wind protons into the wake along IMF, (ii) the solar wind protons with finite gyro-radii that are aided by the wake boundary electric field, (iii) solar wind protons with gyro-radii larger than lunar radii from the tail of the solar wind velocity distribution, and (iv) scattering of solar wind protons from the dayside lunar surface or from magnetic anomalies. In order to gain more insight into the entry mechanisms associated with different populations, backtracing is carried out for each of these populations. For most of the populations, the source of the protons obtained from backtracing is found to be in agreement with that inferred from the velocity distribution. There are few populations that could not be explained by the known mechanisms and remain unknown.Comment: 8 figures, paper accepted in Icarus (2016), http://dx.doi.org/10.1016/j.icarus.2016.01.03

Studying the Lunar-Solar Wind Interaction with the SARA Experiment aboard the Indian Lunar Mission Chandrayaan-1

The first Indian lunar mission Chandrayaan-1 was launched on 22 October 2008. The Sub-keV Atom Reflecting Analyzer (SARA) instrument onboard Chandrayaan-1 consists of an energetic neutral atom (ENA) imaging mass analyzer called CENA (Chandrayaan-1 Energetic Neutrals Analyzer), and an ion-mass analyzer called SWIM (Solar wind Monitor). CENA performed the first ever experiment to study the solar wind-planetary surface interaction via detection of sputtered neutral atoms and neutralized backscattered solar wind protons in the energy range ~0.01-3.0 keV. SWIM measures solar wind ions, magnetosheath and magnetotail ions, as well as ions scattered from lunar surface in the ~0.01-15 keV energy range. The neutral atom sensor uses conversion of the incoming neutrals to positive ions, which are then analyzed via surface interaction technique. The ion mass analyzer is based on similar principle. This paper presents the SARA instrument and the first results obtained by the SWIM and CENA sensors. SARA observations suggest that about 20% of the incident solar wind protons are backscattered as neutral hydrogen and ~1% as protons from the lunar surface. These findings have important implications for other airless bodies in the solar system.Comment: 4 pages, 6 figure