Langmuir Probe Experiment Research Articles

Double‐ejection micro‐cathode arc thruster applied to micro‐satellite

An innovative double-ejection micro-cathode arc thruster (ACd-µCAT), which consists of a cylindrical inner anode, a cylindrical outer cathode and two insulating sleeves (an inner insulating sleeve and an outer insulating sleeve), was proposed. The differences in electrical characteristics, plasma parameters and propulsion performance between the newly proposed ACd-µCAT and a traditional μCAT were examined. Study results showed that compared to the traditional μCAT structure, by using the ACd-µCAT, the peak value of produced thrust was increased 9.3 times, while the amplitude of the ion current and the ion-to-arc ratio were increased 5.4 and 5.9 times (from 1.2% to 7.1%), respectively. In addition, data from Langmuir probe experiments indicated that peak values of the directional propagation speed and density of plasma plume were increased 3.1 times and 4.2 times, respectively. Moreover, plasma plume directional ejection performance was also significantly improved. This study result will provide support for the development of a new-generation μCAT.

IONOSPHERIC PLASMA VARIATIONS AFORE THE EAST OF KURIL ISLANDS EARTHQUAKE OF 13th JANUARY, 2007

Plasma Analyzer (IAP) and Langmuir Probe (ISL) experiments of the DEMETER microsatellite were used to check the state of the ionosphere in the region of the M8.1 East of Kuril Islands earthquake of 13th January, 2007,30 days afore and 10 days after the event using statistical approach. The study strongly revealed that all three investigated ionospheric parameters of electron density, total ion density and electron temperature displayed unfamiliar ionospheric variations eight days before the earthquake in the daytime time half orbit measurement. To this, the electron density, total ion density and electron temperature recorded a variation of 4.09, 5.73 and -2.03 respectively. These irregularities were vetted for untrue signals using the geomagnetic indices of Kp and Dst. It was however realized that the state of the ionosphere was geomagnetically quiet during this day, hence the observed variations were seismogenic.

Using Magnetic Topology to Probe the Sources of Mars' Nightside Ionosphere

AbstractWe combine thermal electron densities in Mars' ionosphere with magnetic topology information to investigate the sources of the nightside ionosphere. Thermal electron density is measured in situ by the Langmuir Probe and Waves experiment onboard Mars Atmospheric and Volatile EvolutioN, while magnetic topology is simultaneously inferred from suprathermal electron energy‐pitch angle distributions measured by the Solar Wind Electron Analyzer and the Magnetometer. Topologically closed regions inhibit electron impact ionization, allowing us to isolate the effects of plasma transport from the dayside, which exhibits a dawn‐dusk asymmetry. Pressure gradient forces on open magnetic field lines connected to the dayside ionosphere source the high‐altitude nightside ionosphere, resulting in higher densities. Regions that are topologically open to the nightside ionosphere allow us to assess in situ production by electron impact ionization, which is responsible for ~50% of the nightside ionosphere below ~160 km and ~25% above ~220 km (on average).

Microwave power absorption to high energy electrons in the ECR ion thruster

The microwave power absorption efficiency of the μ10 ECR ion thruster, utilized in the Japanese asteroid explorers Hayabusa and Hayabusa2, is investigated in order to allow performance measurement and provide information for its improvement. A model detailing the local electron behavior in a real ECR plasma discharge, based the magnetic field characteristics, is presented. Three methods to evaluate the microwave power absorption efficiency are proposed: an estimation based on the chamber geometry and magnetic field characteristics, a measuremen based on performance parameters and a measurement performed with Langmuir probes. The equations used for each method are analytically derived. The local electron behavior model is confirmed with a Langmuir probe experiment. Measurement of the microwave power absorption efficiency is performed with the two independent methods proposed. Results from the two experiments show good agreement with each other and with the theory. Finally, a diffusion model explaining the different electron temperature distributions observed in the chamber is proposed. The model and experiments clarify the physics behind previously observed performance variations and give valuable hints for future chamber improvement.

Langmuir probe plasma diagnostics to investigate the dielectric properties of cryogenic gas mixtures

Use of the Langmuir probe plasma diagnostics to investigate the dielectric properties of gas mixtures is discussed as a continuation our previous experimental and theoretical work on understanding the dielectric strength of helium gas mixtures for superconducting and other cryogenic applications. Here we report the results of Langmuir probe experiments conducted on the gas mixtures to obtain plasma parameters including plasma density and the electron temperature. The experimental procedure used in the Langmuir probe plasma measurements, the derivation of the plasma characteristic parameters, and the implications of the results to the dielectric characteristics are discussed. The plasma characteristics obtained under various discharge power, gas pressure, and gas composition are also discussed. The results support the findings of the our previous theoretical and experimental studies that showed substantial enhancement of dielectric strength of He gas obtained by the addition of small mol% of H2 and relate the enhancements to the plasma characteristics observed.

Electron energetics in the Martian dayside ionosphere: Model comparisons with MAVEN data

AbstractThis paper presents a study of the energetics of the dayside ionosphere of Mars using models and data from several instruments on board the Mars Atmosphere and Volatile EvolutioN spacecraft. In particular, calculated photoelectron fluxes are compared with suprathermal electron fluxes measured by the Solar Wind Electron Analyzer, and calculated electron temperatures are compared with temperatures measured by the Langmuir Probe and Waves experiment. The major heat source for the thermal electrons is Coulomb heating from the suprathermal electron population, and cooling due to collisional rotational and vibrational CO2 dominates the energy loss. The models used in this study were largely able to reproduce the observed high topside ionosphere electron temperatures (e.g., 3000 K at 300 km altitude) without using a topside heat flux when magnetic field topologies consistent with the measured magnetic field were adopted. Magnetic topology affects both suprathermal electron transport and thermal electron heat conduction. The effects of using two different solar irradiance models were also investigated. In particular, photoelectron fluxes and electron temperatures found using the Heliospheric Environment Solar Spectrum Radiation irradiance were higher than those with the Flare Irradiance Spectrum Model‐Mars. The electron temperature is shown to affect the O2+ dissociative recombination rate coefficient, which in turn affects photochemical escape of oxygen from Mars.

Coordinated in situ measurements of plasma irregularities and ground based scintillation observations at the crest of equatorial anomaly

First comparison of in situ density fluctuations measured by the DEMETER satellite with ground based GPS receiver measurements at the equatorial anomaly station Bhopal (geographic coordinates (23.2°N,77.6°E); geomagnetic coordinates (14.29°N,151.12°E)) for the low solar activity year 2005, are presented in this paper. Calculation of the diurnal maximum of the strength of the equatorial electrojet, which can serve as precursor to ionospheric scintillations in the anomaly region is also done. The Langmuir Probe experiment and Plasma Analyzer onboard DEMETER measure the electron and ion densities respectively. Irregularities in electron density distribution cause scintillations on transionospheric links and there exists a close relationship between an irregularity and scintillation. In 40% of the cases, DEMETER detects the irregularity structures (dNe/Ne⩾5% and dNi/Ni (O+)⩾5%) and GPS L band scintillations (S4⩾0.2) are also observed around the same time, for the low solar activity period. It is found that maximum irregularity intensity is obtained in the geomagnetic latitude range of 10–20° for both electron density and ion density. As the GPS signals pass through this irregularity structure, scintillations are recorded by the GPS receiver installed at the equatorial anomaly station, Bhopal it is interesting to note that in situ density fluctuations observed on magnetic flux tubes that pass over Bhopal can be used as indicator of ionospheric scintillations at that site. Many cases of density fluctuations and associated scintillations have been observed during the descending low solar activity period. The percentage occurrence of density irregularities and scintillations shows good correspondence with diurnal maximum of the strength of electrojet, however this varies with different seasons with maximum correspondence in summer (up to 66%) followed by equinox (up to 50%) and winter (up to 46%). Also, there is a threshold value of EEJ strength to produce density irregularities ((dNe/Ne)max⩾5%) and for moderate to strong scintillations (S4⩾0.3) to occur. For winter this value is found to be ∼40nT whereas for equinox and summer it is around 50nT.

Means to remove electrode contamination effect of Langmuir probe measurement in space

Precaution to remove the serious effect of electrode contamination in Langmuir probe experiments has not been taken in many space measurements because the effect is either not understood or ignored. We stress here that one should pay extra attention to the electrode contamination effect to get accurate and reliable plasma measurements so that the long time effort for sounding rocket/satellite missions does not end in vain or becomes less fruitful. In this paper, we describe two main features of voltage-current characteristic curves associated with the contaminated Langmuir probe, which are predicted from the equivalent circuit model, which we proposed in 1970's. We then show that fast sweeping dc Langmuir probes can give reliable results in the steady state regime. The fast sweeping probe can also give reliable results in transient situations such as satellite moves through plasma bubble in the ionosphere where the electron density drastically changes. This fact was first confirmed in our laboratory experiment.

Investigation of VLF and HF waves showing seismo-ionospheric anomalies induced by the 29 September 2009 Samoa earthquake (<i>M</i><sub>w</sub>=8.1)

Abstract. In Samoa Islands, a powerful earthquake took place at 17:48:10.99 UTC (06:48:10.99 LT) on 29 September 2009 with a magnitude Mw=8.1. Using ICE (Instrument Champ Electrique) and IMSC (Instrument Magnetic Search Coil) experiments onboard the DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite we have surveyed possible variations in electromagnetic signals transmitted by the ground-based VLF transmitter NPM in Hawaii and in HF plasma waves close to the Samoa earthquake during the seismic activity. The indices Dst and Kp were used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic activities. In a previous study we have shown that anomalies in IAP (plasma analyzer) and ISL (Langmuir probe) experiments onboard the DEMETER and also TEC (Total Electron Content) data appear 1 to 5 days before the Samoa earthquake. In this paper we show that the anomalies in the VLF transmitter signal and in the HF range appear with the same time scale. The lack of significant geomagnetic activities indicates that these anomalous behaviors could be regarded as seismo-ionospheric precursors. It is also shown that comparative analysis is more effective in seismo-ionospheric studies.

Observations of electron density and electron temperature during large scale magnetic fields in the dayside Venus ionosphere and lesson for Mars

We first present several dayside electron density (Ne) and electron temperature (Te) profiles observed by the Langmuir probe experiment aboard Pioneer Venus Orbiter when the Venus ionosphere was in a magnetised state and then examine the effect of large scale magnetic fields on the Venus ionosphere. We find that for the magnetised ionospheres, the “top” moves down to altitudes near 200 km and the ionopause layers with steep altitude gradients in Ne and Te start above this altitude. No significant change in electron density and electron temperature is seen within the ionosphere. Occasionally a second ionopause layer is also seen at higher altitudes and the ionospheric region between the two ionopause layers, which is seen to extend to altitudes up to 250 km, too does not indicate any significant change in Ne and Te for these cases. These results have direct relevance to Mars where large scale ionospheric fields have also been observed.

Electron and ion density variations before strong earthquakes (<i>M</i>>6.0) using DEMETER and GPS data

Abstract. Using IAP (plasma analyzer) and ISL (Langmuir probe) experiments onboard DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite and GPS (Global Positioning System) measurements, we have statistically analyzed the variations of the electron and ion densities to search for disturbances in the vicinity of four large earthquakes prior to events. The indices Dst and Kp were used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic activities. For each studied case, a very good agreement was found between the different parameters estimated by DEMETER and GPS data in the detection of pre-seismic anomalies. Our statistics results show that the anomalous deviations prior to earthquakes have different sign from case to case, and that their amplitude depends on the magnitude of the earthquake. It has also been found that the electron density measured by the ISL experiment at night detects anomalous variations significantly before the earthquakes. The appearance of positive and negative anomalies in both of DEMETER and TEC (Total Electron Content) data during 1 to 5 days before all studied earthquakes during quiet geomagnetic conditions indicates that these anomalous behaviors are highly regarded as seismo-ionospheric precursors.

Measurements of EEDF in recombination dominated afterglow plasma

Electron energy distribution functions (EEDF) have been measured in decaying plasma in Flowing Afterglow Langmuir Probe (FALP) experiment. The measurements have been carried out in diffusion and recombination governed plasmas used for studies of recombination of KrD+ and H3+ ions.

Measurements of EEDF in Helium Flowwing Afterglow at Pressures 500 – 2000 PA

AbstractFor measurements of recombination rate coefficients of slowly recombining ions with rate coefficients below 10–7cm3s–1 in Flowing Afterglow Langmuir Probe (FALP) experiment the plasma decay time has to be long and this requires buffer gas (helium) pressures in range 500 – 2000 Pa. Application of Langmuir probe for measurements of electron energy distribution function, EEDF (f (ε)), at these pressures is not trivial. The Druyvestein formula for calculating f (ε) from the second derivative of the electron current to the probe (I″e) cannot be used. More complex analyses of measured probe characteristic are required to obtain reliable EEDF. To characterize the extent of the required corrections, the probe characteristics in well‐defined flowing afterglow plasma were measured and two different methods were used to obtain EEDF. In the first method, the first and second derivative of probe characteristics were used to obtain EEDF [1]. In the second method, numerical correction was calculated [2] and applied to values obtained from Druyvesteyn formula. By comparison of obtained EEDF with Maxwell distribution we determine a region of electron energies where advanced analysis is necessary. It was found that in a helium afterglow at 250 K, with pressure 600 – 2000 Pa, where plasma is nearly Maxwellian with T e ∼ 250 – 600 K, the correction is necessary for electron energies ε ≤ 3.5 kBTe. At higher electron energies correction is negligible and is not necessary. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Application of Langmuir Probe in Recombination Dominated Afterglow Plasma

AbstractNew advanced data analysis method for calculation of recombination rate coefficients from the decay of electron density during the afterglow (along the flow tube) in a Flowing Afterglow Langmuir Probe (FALP) experiment is presented. The method is advantageous for measurements of recombination rate coefficients of slowly recombining ions in conditions where formation of the studied ions is slow, decaying plasma contains several types of ions and the ion formation and recombination proceed simultaneously. The new method is demonstrated on the analysis of the data obtained from plasma decay in He/Kr/H2 and He/Kr/D2 gas mixtures. In a limit for [Kr]/[D2] ≫ 1, the recombination rate coefficients for KrD+ ions α (KrD+, 250 K) = 1 × 108cm3s–1 was obtained. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The ISL Langmuir probe experiment processing onboard DEMETER: Scientific objectives, description and first results

The DEMETER Langmuir probe experiment, called “Instrument Sonde de Langmuir” (ISL), has been designed for in situ measurements of the bulk parameters of the ionospheric thermal plasma. The ISL instrument is comprised of two sensors: (i) a classical cylindrical sensor and (ii) a spherical sensor with its surface divided in seven segments: six spherical caps electrically isolated and the rest of the sphere which is used as a guard electrode. The two main parameters measured by ISL are the electron density and temperature; they are obtained with a 1 s time-resolution. In addition, the ion density and its variation can be derived from the current-voltage characteristics of the probe, but it requires an a-priori knowledge of the ion composition and a more sophisticated processing than the one currently implemented. The novel design for the spherical sensor has been called the segmented Langmuir probe (SLP). The SLP current can be measured individually on each of the seven segments, thus providing angular sensitivity to the ram direction of the incoming ion flow. The SLP was flown for the first time onboard the DEMETER satellite for in-flight validation of this novel concept, but the main sensor used routinely during the mission is the cylindrical probe. The design of the instrument and the analysis technique for the cylindrical probe are described. A brief description of the SLP and of its capabilities is provided. An overview of the currently available ISL data products on the DEMETER Mission Science Data Centre is given. Selected examples of some “classical” ionospheric features as being observed by ISL are discussed.

Science opportunities with a double Langmuir probe and electric field experiment for JIMO

The three icy Galilean moons of Jupiter: Callisto, Ganymede, and Europa, offer a range of exciting science opportunities for space physics and aeronomy. They all have thin atmospheres with residence times of a few days at most. The surface interactions with the space environment determine the atmospheric and ionospheric properties. The Jupiter Icy Moons Orbiter (JIMO) gives possibilities to investigate the weathering properties of their surfaces and volatile material expelled from their interiors. The atmospheres and the ionized ionospheric components of the Galilean moons (including the volcanic moon Io) interact strongly with the co-rotating magnetosphere of Jupiter. This interaction is dynamic and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. The icy moon’s ionospheres are likewise highly variable in time and estimated peak electron densities vary between 1000 and 20,000 cm −3 near their surfaces. A particularly interesting interaction occurs between the magnetosphere of Jupiter and the mini-magnetosphere of Ganymede and its ionosphere. A double-Langmuir probe (LP) experiment orbiting the moons at a short distance for several months will give valuable insight into these processes. Foremost the LP measures in situ plasma density and temperatures of the ionospheric components of the moons with high time resolution and thereby provides estimates of key parameters for the dynamical behaviour of surface weathering and magnetospheric influences. In addition many other physical parameters important to the dynamics of these systems can be estimated with such an instrument, like the plasma flow and the DC electric field. Recent results from the LP part of the Radio and Plasma Wave Science (RPWS) on board the Cassini/Huygens spacecraft orbiting Saturn show that an LP works in extended plasma parameter domains with very good science return.

Two stream instability in E region over magnetic equator during morning hours

Abstract Rocketborne Langmuir probe experiments conducted from Thumba (8.5°N, 77°E, mag. lat. 0.5°N), India during morning hours have shown the existence of two stream instability in the altitude region of 105 km. Two stream instability is excited when drift velocity of electron exceeds the ion acoustic velocity in the medium.

Hardware and software systems for the determination of charged particle parameters in low pressure plasmas using impedance-tuned langmuir probes

Abstract A computer-controlled, impedance-tuned Langmuir probe data acquisition system and processing software package have been designed for the diagnostic study of low pressure plasmas. The combination of impedance-tuning and a wide range of applied potentials (± 100 V) provides a versatile system, applicable to a variety of analytical plasmas without significant modification. The automated probe system can be used to produce complete and undistorted current-voltage (i-V) curves with extremely low noise over the wide potential range. Based on these hardware and software systems, it is possible to determine all of the important charged particle parameters in a plasma; electron number density ( n e ), ion number density ( n i ), electron temperature ( T e ), electron energy distribution function (EEDF), and average electron energy (〈e〉). The complete data acquisition system and evaluation software are described in detail. A LabView (National Instruments Corporation, Austin, TX) application program has been developed for the Apple Macintosh line of microcomputers to control all of the operational aspects of the Langmuir probe experiments. The description here is mainly focused on the design aspects of the acquisition system with the targets of extremely low noise and reduction of the influence of measurement noise in the calculation procedures. This is particularly important in the case of electron energy distribution functions where multiple derivatives are calculated from the obtained i-V curves. A separate C-language data processing program has been developed and is included here to allow the reader to evaluate data obtained with the described hardware, or any i-V data imported in tab separated variable format. Both of the software systems are included on a Macintosh formatted disk for their use in other laboratories desiring these capabilities.

Hardware and software systems for the determination of charged particle parameters in low pressure plasmas using impedance-tuned Langmuir probes

A computer-controlled, impedance-tuned Langmuir probe data acquisition system and processing software package have been designed for the diagnostic study of low pressure plasmas. The combination of impedance-tuning and a wide range of applied potentials (± 100 V) provides a versatile system, applicable to a variety of analytical plasmas without significant modification. The automated probe system can be used to produce complete and undistorted current-voltage (i-V) curves with extremely low noise over the wide potential range. Based on these hardware and software systems, it is possible to determine all of the important charged particle parameters in a plasma; electron number density ( n e ), ion number density ( n i ), electron temperature ( T e ), electron energy distribution function (EEDF), and average electron energy (〈ε〉). The complete data acquisition system and evaluation software are described in detail. A LabView (National Instruments Corporation, Austin, TX) application program has been developed for the Apple Macintosh line of microcomputers to control all of the operational aspects of the Langmuir probe experiments. The description here is mainly focused on the design aspects of the acquisition system with the targets of extremely low noise and reduction of the influence of measurement noise in the calculation procedures. This is particularly important in the case of electron energy distribution functions where multiple derivatives are calculated from the obtained i-V curves. A separate C-language data processing program has been developed and is included here to allow the reader to evaluate data obtained with the described hardware, or any i-V data imported in tab separated variable format. Both of the software systems are included on a Macintosh formatted disk for their use in other laboratories desiring these capabilities.

Electron densities in the equatorial lower ionosphere over Thumba and SHAR

The paper presents thirty electron density profiles obtained by rocket-borne Langmuir probe experiments conducted from Thumba, India (8°52′N, 76°87′E, dip 0°45′S). We consider for comparison six electron density profiles using the same technique from SHAR, India which is just outside the electrojet region. With the exception of two flights during counter electrojet (CEJ) condition, the Thumba flights correspond to daytime normal electrojet (NEJ) condition. The profiles over Thumba were very smooth, the electron density increased monotonously with increasing altitude. The increase above 100 km was much slower. Night, morning and eveningtime profiles over Thumba show pronounced structures. Most profiles show a maximum around 110 km and a valley around 130 km. For SHAR one daytime, two evening twilight and three nighttime profiles are presented. In general, the profiles over SHAR show a lot more structures as compared to Thumba profiles.