scholarly journals Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission

2019 ◽  
Vol 630 ◽  
pp. A39 ◽  
Author(s):  
H. Breuillard ◽  
P. Henri ◽  
L. Bucciantini ◽  
M. Volwerk ◽  
T. Karlsson ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Compressional Waves ◽  
Weibel Instability ◽  
Plasma Environment ◽  
Background Magnetic Field ◽  
Rosetta Mission ◽  
Ion Waves ◽  
Plasma Coupling

Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. We take advantage of a cometary outburst event that occurred on 2016 February 19 to probe this generation mechanism. We analyze the 3D magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. They are observed in the typical frequency range (~50 mHz) before the cometary outburst, but at ~20 mHz during the outburst. They are also observed to be elliptically right-hand polarized and to propagate rather closely (~0−50°) to the background magnetic field. We also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. The correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. We therefore show that the measurements from multiple instruments are consistent with the modified ion-Weibel instability as the source of the singing comet wave activity. We also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67P environment.

Kinetic simulations of high Mach shocks: PIC simulations vs in-situ measurements

2021 ◽  
Author(s):  
Artem Bohdan ◽  
Martin Pohl ◽  
Jacek Niemiec ◽  
Paul J. Morris ◽  
Yosuke Matsumoto ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Mach Number ◽  
Supernova Remnants ◽  
Large Scale ◽  
Bow Shock ◽  
Electron Heating ◽  
Weibel Instability ◽  
High Mach Number ◽  
High Mach

<p>High-Mach-number collisionless shocks are found in planetary systems and supernova remnants (SNRs). Electrons are heated at these shocks to temperatures well above the Rankine–Hugoniot prediction. However, the processes responsible for causing the electron heating are still not well understood. We use a set of large-scale particle-in-cell simulations of nonrelativistic shocks in the high-Mach-number regime to clarify the electron heating processes. The physical behavior of these shocks is defined by ion reflection at the shock ramp. Further interactions between the reflected ions and the upstream plasma excites electrostatic Buneman and two-stream ion–ion Weibel instabilities. Electrons are heated via shock surfing acceleration, the shock potential, magnetic reconnection, stochastic Fermi scattering, and shock compression. The main contributor is the shock potential. The magnetic field lines become tangled due to the Weibel instability, which allows for parallel electron heating by the shock potential. The constrained model of electron heating predicts an ion-to-electron temperature ratio within observed values at SNR shocks and in Saturn’s bow shock. We also present evidence for field amplification by the Weibel instability. The normalized magnetic field strength strongly correlates with the Alfvenic Mach number, as is in-situ observed at Saturn's bow shock.</p>

In Situ Observation of Chymotrypsin Catalytic Activity Change Actuated by Nonheating Low-Frequency Magnetic Field

ACS Nano ◽  
2018 ◽  
Vol 12 (4) ◽  
pp. 3190-3199 ◽  
Author(s):  
Maria V. Efremova ◽  
Maxim M. Veselov ◽  
Alexander V. Barulin ◽  
Sergey L. Gribanovsky ◽  
Irina M. Le-Deygen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Catalytic Activity ◽  
Low Frequency ◽  
In Situ Observation ◽  
Activity Change ◽  
Frequency Magnetic Field

scholarly journals Spatial Averaging Schemes of In Situ Electric Field for Low-Frequency Magnetic Field Exposures

IEEE Access ◽  
2019 ◽  
Vol 7 ◽  
pp. 184320-184331 ◽  
Author(s):  
Yinliang Diao ◽  
Jose Gomez-Tames ◽  
Essam A. Rashed ◽  
Robert Kavet ◽  
Akimasa Hirata
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Low Frequency ◽  
Spatial Averaging ◽  
Frequency Magnetic Field

scholarly journals Magnetic Field Mapping and Correction for Moving OP-MEG

2021 ◽  
Author(s):  
Stephanie J Mellor ◽  
Tim M Tierney ◽  
George C O'Neill ◽  
Nicholas Alexander ◽  
Robert A Seymour ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Brain Activity ◽  
Low Frequency ◽  
Optically Pumped ◽  
Magnetic Field Mapping ◽  
Modelling Method ◽  
Movement Artefact ◽  
Power Spectral ◽  
Background Magnetic Field ◽  
The Magnetic Field

Background: Optically pumped magnetometers (OPMs) have made moving, wearable magnetoencephalography (MEG) possible. The OPMs typically used for MEG require a low background magnetic field to operate, which is achieved using both passive and active magnetic shielding. However, the background magnetic field is never truly zero Tesla, and so the field at each of the OPMs changes as the participant moves. This leads to position and orientation dependent changes in the measurements, which manifest as low frequency artefacts in MEG data. Objective: We modelled the spatial variation in the magnetic field and used the model to predict the movement artefact found in a dataset. Methods: We demonstrate a method for modelling this field with a triaxial magnetometer, then showed that we can use the same technique to predict the movement artefact in a real OPM-based MEG (OP-MEG) dataset. Results: Using an 86-channel OP-MEG system, we found that this modelling method maximally reduced the power spectral density of the data by 26.2 ± 0.6 dB at 0 Hz, when applied over 5 s non-overlapping windows. Conclusion: The magnetic field inside our state-of-the art magnetically shielded room can be well described by low-order spherical harmonic functions. We achieved a large reduction in movement noise when we applied this model to OP-MEG data. Significance: Real-time implementation of this method could reduce passive shielding requirements for OP-MEG recording and allow the measurement of low-frequency brain activity during natural participant movement.

scholarly journals On ion gyro-harmonic structuring in the stimulated electromagnetic emission spectrum during second electron gyro-harmonic heating

2012 ◽  
Vol 30 (11) ◽  
pp. 1587-1594 ◽  
Author(s):  
A. Samimi ◽  
W. A. Scales ◽  
P. A. Bernhardt ◽  
S. J. Briczinski ◽  
C. A. Selcher ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Electromagnetic Emission ◽  
Spectral Lines ◽  
Critical Parameters ◽  
Pump Field ◽  
Pump Frequency ◽  
Ionospheric Heating ◽  
Background Magnetic Field ◽  
Stimulated Electromagnetic Emission

Abstract. Recent observations show that, during ionospheric heating experiments at frequencies near the second electron gyro-harmonic, discrete spectral lines separated by harmonics of the ion-gyro frequency appear in the stimulated electromagnetic emission (SEE) spectrum within 1 kHz of the pump frequency. In addition to the ion gyro-harmonic structures, on occasion, a broadband downshifted emission is observed simultaneously with these spectral lines. Parametric decay of the pump field into upper hybrid/electron Bernstein (UH/EB) and low-frequency ion Bernstein (IB) and oblique ion acoustic (IA) modes is considered responsible for generation of these spectral features. Guided by predictions of an analytical model, a two-dimensional particle-in-cell (PIC) computational model is employed to study the nonlinear processes during such heating experiments. The critical parameters that affect the spectrum, such as whether discrete gyro-harmonic on broadband structures is observed, include angle of the pump field relative to the background magnetic field, pump field strength, and proximity of the pump frequency to the gyro-harmonic. Significant electron heating along the magnetic field is observed in the parameter regimes considered.

scholarly journals A radiation hardened digital fluxgate magnetometer for space applications

2013 ◽  
Vol 2 (2) ◽  
pp. 213-224 ◽  
Author(s):  
D. M. Miles ◽  
J. R. Bennest ◽  
I. R. Mann ◽  
D. K. Millling
Keyword(s):  
Magnetic Field ◽  
Temperature Compensation ◽  
Low Frequency ◽  
Radiation Belts ◽  
Fluxgate Magnetometer ◽  
Science Data ◽  
Space Applications ◽  
Outer Radiation Belt ◽  
Background Magnetic Field ◽  
New Instrument

Abstract. Space-based measurements of Earth's magnetic field are required to understand the plasma processes responsible for energising particles in the Van Allen radiation belts and influencing space weather. This paper describes a prototype fluxgate magnetometer instrument developed for the proposed Canadian Space Agency's (CSA) Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite (ORBITALS) mission and which has applications in other space and suborbital applications. The magnetometer is designed to survive and operate in the harsh environment of Earth's radiation belts and measure low-frequency magnetic waves, the magnetic signatures of current systems, and the static background magnetic field. The new instrument offers improved science data compared to its predecessors through two key design changes: direct digitisation of the sensor and digital feedback from two cascaded pulse-width modulators combined with analog temperature compensation. These provide an increase in measurement bandwidth up to 450 Hz with the potential to extend to at least 1500 Hz. The instrument can resolve 8 pT on a 65 000 nT field with a magnetic noise of less than 10 pT/√Hz at 1 Hz. This performance is comparable with other recent digital fluxgates for space applications, most of which use some form of sigma-delta (ΣΔ) modulation for feedback and omit analog temperature compensation. The prototype instrument was successfully tested and calibrated at the Natural Resources Canada Geomagnetics Laboratory.

In-situ evaluation of low-frequency magnetic field fluctuation in an atomic comagnetometer

2021 ◽  
pp. 1-1
Author(s):  
Jiong Huang ◽  
Zhuo Wang ◽  
Wenfeng Fan ◽  
Haoying Pang ◽  
Kai Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Field Fluctuation ◽  
Magnetic Field Fluctuation ◽  
Frequency Magnetic Field

Solar wind protons in the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko

2021 ◽  
Author(s):  
Charlotte Goetz ◽  
Lucie Scharre ◽  
Cyril Simon-Wedlund ◽  
Hans Nilsson ◽  
Elias Odelstad ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Gas Production ◽  
Alpha Particles ◽  
Cometary Plasma ◽  
Plasma Environment ◽  
Rosetta Mission ◽  
Show Evidence ◽  
Solar Wind Origin ◽  
Comet 67P

<p>Against expectations, the Rosetta spacecraft was able to observe protons of solar wind origin in the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko. This study investigates these unexpected observations and gives a working hypothesis on what could be the underlying cause.</p> <p>The cometary plasma environment of a comet is shaped by two distinct plasma populations: the solar wind, consisting of protons, alpha particles, electrons and a magnetic field, and the cometary plasma, consisting of heavy ions such as water ions or carbon dioxide ions and electrons. <br />As the comet follows its orbit through the solar system, the amount of cometary ions that is produced varies significantly. This means that the plasma environment of the comet and the boundaries that form there are also dependent on the comet's heliocentric distance. </p> <p>For example, at sufficiently high gas production rates (close to the Sun) the protons from the solar wind are prevented from entering the inner coma entirely. The region where no protons (and other solar wind origin ions) can be detected is referred to as the solar wind ion cavity. <br />A second example is the diamagnetic cavity, a region very close to the nucleus of the comet, where the interplanetary magnetic field, which is carried by the solar wind electrons, cannot penetrate the densest part of the cometary plasma. </p> <p>The Rosetta mission clearly showed that the solar wind ion cavity is larger than the diamagnetic cavity at a comet such as 67P/Churyumov-Gerasimenko. However, this new study finds that in isolated incidences this order can be reversed and ions of solar wind origin (mostly protons, but also helium) can be detected inside the diamagnetic cavity. We present the observations pertaining to these events and list and discard possible mechanisms that could lead to such a configuration. Only one mechanism cannot be discarded: that of a solar wind configuration where the solar wind velocity is aligned with the magnetic field. We show evidence that fits this hypothesis as well as solar wind models in support. </p>

scholarly journals Low-frequency magnetic field fluctuations in Earth's plasma environment observed by THEMIS

2012 ◽  
Vol 30 (8) ◽  
pp. 1271-1283 ◽  
Author(s):  
L. Guicking ◽  
K.-H. Glassmeier ◽  
H.-U. Auster ◽  
Y. Narita ◽  
G. Kleindienst
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Wave Generation ◽  
Wave Activity ◽  
Wave Intensity ◽  
Magnetic Wave ◽  
Plasma Environment ◽  
Frequency Magnetic Field ◽  
Field Fluctuations ◽  
Generation Mechanisms

Abstract. Low-frequency magnetic wave activity in Earth's plasma environment was determined based on a statistical analysis of THEMIS magnetic field data. We observe that the spatial distribution of low-frequency magnetic field fluctuations reveals highest values in the magnetosheath, but the observations differ qualitatively from observations at Venus presented in a previous study since significant wave activity at Earth is also observed in the nightside magnetosheath. Outside the magnetosheath the low-frequency wave activity level is generally very low. By means of an analytical streamline model for the magnetosheath plasma flow, we are able to investigate the spatial and temporal evolution of wave intensity along particular streamlines in order to characterise possible wave generation mechanisms. We observe a decay of wave intensity along the streamlines, but contrary to the situation at Venus, we obtain good qualitative agreement with the theoretical concept of freely evolving/decaying turbulence. Differences between the dawn region and the dusk region can be observed only further away from the magnetopause. We conclude that wave generation mechanisms may be primarily attributed to processes at or in the vicinity of the bow shock. The difference with the observations of the Venusian magnetosheath we interpret to be the result of the different types of solar wind interaction processes since the Earth possesses a global magnetic field while Venus does not, and therefore the observed magnetic wave activities may be caused by diverse magnetic field controlled characteristics of wave generation processes.

scholarly journals A radiation hardened digital fluxgate magnetometer for space applications

2013 ◽  
Vol 3 (1) ◽  
pp. 31-58
Author(s):  
D. M. Miles ◽  
J. R. Bennest ◽  
I. R. Mann ◽  
D. K. Millling
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Radiation Belts ◽  
Digital Design ◽  
Fluxgate Magnetometer ◽  
Science Data ◽  
Space Applications ◽  
Outer Radiation Belt ◽  
Background Magnetic Field ◽  
New Instrument

Abstract. Space-based measurements of the Earth's magnetic field are required to understand the plasma processes responsible for energizing particles in the Van Allen radiation belts and influencing space weather. This paper describes a prototype fluxgate magnetometer instrument developed for the proposed Canadian Space Agency (CSA) Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite (ORBITALS) mission and which has applications in other space and suborbital applications. The magnetometer is designed to survive and operate in the harsh environment of the Earth's radiation belts and measure low-frequency magnetic waves, the magnetic signatures of current systems, and the static background magnetic field. The new instrument offers improved science data compared to its predecessors through two key design changes: direct digitisation of the sensor and digital feedback combined with analog temperature compensation. These provide an increase in measurement bandwidth up to 450 Hz with the potential to extend to at least 1500 Hz. The instrument can resolve 8 pT on a 65 000 nT field with a magnetic noise of less than 10 pT per square–root Hz at 1 Hz. The prototype instrument was successfully tested and calibrated at the Natural Resources Canada Geomagnetics Laboratory showing that the mostly-digital design matches or exceeds its radiation-soft analog predecessor in sensitivity, noise, frequency range, and RMS accuracy.

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