Observation of MHD Instabilities Driven by Energetic Electrons in the Large Helical Device

Coherent magnetic fluctuations in an acoustic range of frequency have been regularly observed in low-density（n_e〈0.2×10^（19）m^（-3））plasmas with strong second harmonic electron cyclotron resonance heating（ECRH）on the Large Helical Device.Hard X-ray measurements indicated that energetic electrons are generated in these ECRH discharges.The magnetic fluctuations are suppressed in higher density discharges where energetic electrons are not present.The ECRH power modulation experiment indicated that the observed magnetohydrodynamic（MHD）mode has an acoustic nature rather than an Alfvenic nature.

Radial propagation of magnetospheric substorm-injected energetic electrons observed using a BD-IES instrument and Van Allen Probes

In cases where substorm injections can be observed simultaneously by multiple spacecraft,they can help elucidate the potential mechanisms of particle transport and energization,of great importance to understanding and modeling the magnetosphere.In this paper,using data returned from the BeiDa-IES（BD-IES） instrument onboard a satellite in an inclined（55°） geosynchronous orbit（IGSO）,in combination with two geo-transfer orbiting（GTO） satellite Van Allen Probes（A and B）,we analyze a substorm injection event that occurred on the 16 th of October 2015.During this substorm injection,the IGSO onboard BD-IES was outbound,while both Van Allen Probe satellites（A and B） were inbound,a configuration of multiple trajectories that provides a unique opportunity to simultaneously investigate both the inward and outward radial propagation of substorm injection.Indicated by AE/AL indices,this substorm was closely related to an IMF/solar wind discontinuity that showed a sharp change in IMF Bz direction to the north.The innermost signature of this substorm injection was detected by Van Allen Probes A and B at L-3.7,while the outermost signature was observed by the onboard BD-IES instrument at L-10.These data indicate that the substorm had a global,rather than just local,effect.Finally,we suggest that electric fields carried by fast-mode compressional waves around the substorm injection are the most likely candidate mechanism for the electron injection signatures observed in the inner- and outermost inner magnetosphere.

Design of the electron cyclotron emission diagnostic on EXL-50 spherical torus

The electron cyclotron emission(ECE)diagnostic system has been developed on the ENN spherical torus(EXL-50).The ECE system is designed to detect radiation emitted by energetic electrons,rather than conventional 1D electron temperature profile measurement,in the frequency range of 4-40 GHz.The system is composed of five subsystems,each covering a different frequency band,including the C-band(4-8 GHz),X-band(8-12 GHz),Ku-band(12-18 GHz),K-band(18-26.5 GHz)and Kα-band(26.4-40 GHz).The system uses heterodyne detection to analyze the received signals.The K-band and Kα-band subsystems are located horizontally in the equatorial plane of the EXL-50,while the C-band,X-band and Ku-band subsystems are located under the vacuum vessel of the EXL-50.To direct the microwaves from the plasma to the antennas for the horizontal detection subsystems,a quasi-optical system has been developed.For the vertical detection subsystems,the antennas are directly attached to the port located beneath the torus at R=700 mm,which is also the magnetic axis of the torus.The system integration,bench testing and initial experimental results will be thoroughly discussed,providing a comprehensive understanding of the ECE system s performance and capabilities.

Storm-Time Evolution of Energetic Electron Pitch Angle Distributions by Wave-Particle Interaction

The quasi-pure pitch-angle scattering of energetic electrons driven by field-aligned propagating whistler mode waves during the 9～15 October 1990 magnetic storm at L≈ 3 ～ 4 is studied, and numerical calculations for energetic electrons in gyroresonance with a band of frequency of whistler mode waves distributed over a standard Gaussian spectrum is performed. It is found that the whistler mode waves can efficiently drive energetic electrons from the larger pitchangles into the loss cone, and lead to a flat-top distribution during the main phase of geomagnetic storms. This result perhaps presents a feasible interpretation for observation of time evolution of the quasi-isotropic pitch-angle distribution by Combined Release and Radiation Effects Satellite （CRRES） spacecraft at L ≈ 3 ～ 4.

Effect of Chorus Latitudinal Distribution on Evolution of Outer Radiation Belt Electrons

Primary result on the impact of the latitudinal distribution of whistler-mode chorus upon temporal evolution of the phase space density （PSD） of outer radiation belt energetic electrons was presented. We evaluate diffusion rates in pitch angle and momentum due to a band of chorus frequency distributed at a standard Gaussian spectrum, and solve a 2-D bounce-averaged momentum-pitch-angle Fokker-Planck equation at L = 4.5. It is shown that chorus is effective in accelerating electrons and can increase PSD for energy of ～1 MeV by a factor of 10 or more in about one day, which is consistent with observation. Moreover, the latitudinal distribution of chorus has a great impact on the acceleration of electrons. As the latitudinal distribution increases, the efficient acceleration region extends from higher pitch angles to lower pitch angles, and even covers the entire pitch angle region when chorus power reaches the maximum latitude λm = 45°.

Energetic electron detection packages on board Chinese navigation satellites in MEO

Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications.In this paper,the energetic electron detection package(EEDP)deployed on three Chinese navigation satellites in medium Earth orbit(MEO)is reviewed.The instrument was developed by the space science payload team led by Peking University.The EEDP includes a pinhole medium-energy electron spectrometer(MES),a high-energy electron detector(HED)based onΔE-E telescope technology,and a deep dielectric charging monitor(DDCM).The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30°field of view(FOV).The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30°cone-angle FOV.The ground test and calibration results indicate that these three sensors exhibit excellent performance.Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer(MagEIS)of the Van Allen Probes spacecraft,with an average relative deviation of 27.3%for the energy spectra.The charging currents and voltages measured by the DDCM during storms are consistent with the highenergy electron observations of the HED,demonstrating the effectiveness of the DDCM.The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather.

Locating the source field lines of Jovian decametric radio emissions

Decametric(DAM) radio emissions are one of the main windows through which one can reveal and understand the Jovian magnetospheric dynamics and its interaction with the moons. DAMs are generated by energetic electrons through cyclotron-maser instability. For Io(the most active moon) related DAMs, the energetic electrons are sourced from Io volcanic activities, and quickly trapped by neighboring Jovian magnetic field. To properly interpret the physical processes behind DAMs, it is important to precisely locate the source field lines from which DAMs are emitted. Following the work by Hess et al.(2008, 2010), we develop a method to locate the source region as well as the associated field lines for any given DAM emission recorded in a radio dynamic spectrum by, e.g.,Wind/WAVES or STEREO/WAVES. The field lines are calculated by the state-of-art analytical model, called JRM09(Connerney et al., 2018).By using this method, we may also derive the emission cone angle and the energy of associated electrons. If multiple radio instruments at different perspectives observe the same DAM event, the evolution of its source region and associated field lines is able to be revealed. We apply the method to an Io-DAM event, and find that the method is valid and reliable. Some physical processes behind the DAM event are also discussed.

Effect of sheath potential on electromagnetic radiation emitted from the rear surface of a metallic foil target

In ultra-intense laser-matter interactions, intense electric fields formed at the rear surface of a foil target may have strong influences on the motion of energetic electrons, and thereby affect the electromagnetic emissions from the rear surface, usually ascribed to transition radiation. Due to the electric fields, transition radiation occurs twice and bremsstrahlung radiation also happens because the electrons will cross the rear surface twice and have large accelerations. In the optic region, transition radiation is dominant. The radiation spectrum depends on the electric field only when the electrons are monochromatic, and becomes independent of the electric field when the electrons have a broadband momentum distribution. Therefore, in an actual experiment, the electric field at the rear surface of a foil could not be studied just with the measurement of optic emissions. In the terahertz region, both bremsstrahlung and transition radiations should be taken into account, and the radiation power could be enhanced in comparison with that without the inclusion of bremsstrahlung radiation. The frequency at which the maximum terahertz radiation appears depends on the electric field.

Diagnostics from three rising submillimeter bursts

In this paper we investigate three novel rising submillimeter （THz） bursts that occurred sequen- tially in Super Active Region NOAA 10486. The average rising rate of the flux density above 200 GHz is only 20 sfu GHz-1 （corresponding to spectral index α of 1.6） for the THz spectral components of the 2003 October 28 and November 4 bursts, but it attained values of 235 sfu GHz-1 （α = 4.8） in the 2003 November 2 burst. The steeply rising THz spectrum can be produced by a population of highly relativistic electrons with a low-energy cutoff of 1 MeV, but it only requires a low-energy cutoff of 30 keV for the two slowly rising THz bursts, via gyrosynchrotron （GS） radiation based on our numerical simulations of burst spectra in the magnetic dipole field case. The electron density variation is much larger in the THz source than in the microwave （MW） source. It is interesting that the THz source radius decreased by 20%-50% during the decay phase for the three events, but the MW source increased by 28% for the 2003 November 2 event. In the paper we will present a formula that can be used to calculate the energy released by ultrarel- ativistic electrons, taking the relativistic correction into account for the first time. We find that the energy released by energetic electrons in the THz source exceeds that in the MW source due to the strong GS radi- ation loss in the THz range, although the modeled THz source area is 3-4 orders smaller than the modeled MW source one. The total energies released by energetic electrons via the GS radiation in radio sources are estimated, respectively, to be 5.2 × 10^33, 3.9 × 10^33 and 3.7 × 10^32 erg for the October 28, November 2 and 4 bursts, which are 131, 76 and 4 times as large as the thermal energies of 2.9 × 10^31, 2.1 × 10^31 and 5.2 × 10^31 erg estimated from soft X-ray GOES observations.

Reply to Comment by Lamy et al. on “Locating the source field lines of Jovian decametric radio emissions”

Locating the source of decametric(DAM)radio emissions is a key step in the use of remote radio observations to understand the Jovian magnetospheric dynamics and their interaction with the planet’s moons.Wang YM et al.(2020)presented a method by which recorded arc-shaped DAM emissions in the radio dynamic spectra can be used to locate the source of a DAM.An Io-related DAM event on March 14,2014 was used to demonstrate the method.A key parameter in the method is whether the DAM is emitted in the northern or the southern hemisphere;the hemisphere of origin can be determined definitively from the polarization of the emission.Unfortunately,polarization information for the emission on March 14,2014 event was not recorded.Our analysis assumed the source to be in the northern hemisphere.Lamy et al.(2022)argue convincingly that the source was probably in the southern hemisphere.We appreciate the helpful contribution of Lamy et al.(2022)to this discussion and have updated our analysis,this time assuming that the DAM source was in the southern hemisphere.We also explore the sensitivity of our method to another parameter-the height at which the value of fce,max,which is the maximal electron cyclotron frequency reached along the active magnetic flux tube,is adopted.Finally,we introduce our recent statistical study of 68 DAM events,which lays a more solid basis for testing the reliability of our method,which we continue to suggest is a promising tool by which remote radio observations can be used to locate the emission source of Jovian DAMs.

Study of temporal evolution of emission spectrum in a steeply rising submillimeter burst

The temporal evolution of a spectrum during a steeply rising submillimeter（THz） burst that occurred on 2003 November 2 was investigated in detail for the first time.Observations show that the flux density of the THz spectrum increased steeply with frequency above 200 GHz.Their average rising rates reached a value of 235 sfu GHz^（-1）（corresponding to spectral index α of 4.8） during the burst.The flux densities reached about 4 000 and 70 000 sfu at 212 and 405 GHz at the maximum phase,respectively.The emissions at 405 GHz maintained such a continuous high level that they largely exceeded the peak values of the microwave（MW） spectra during the main phase.Our studies suggest that only energetic electrons with a low-energy cutoff of~ 1 MeV and number density of ~ 10~6-10~8 cm^（-3） can produce such a strong and steeply rising THz component via gyrosynchrotron radiation based on numerical simulations of burst spectra in the case of a nonuniform magnetic field.The electron number density N,derived from our numerical fits to the THz temporal evolution spectra,increased substantially from 8 ×10~6 to 4 × 10~8 cm^（-3）,i.e.,the N value increased 50 times during the rise phase.During the decay phase it decreased to 7 ×10~7 cm^（-3）,i.e.,it decreased by about five times from the maximum phase.The total electron number decreased an order of magnitude from the maximum phase to the decay phase.Nevertheless,the variation in amplitude of N is only about one time in the MW emission source during this burst,and the total electron number did not decrease but increased by about 20%during the decay phase.Interestingly,we find that the THz source radius decreased by about 24%while the MW source radius,on the contrary,increased by 28%during the decay phase.

Comparative DFT Study of [Mg(CHZ)_3](ClO_4)_2 and [Mg(CHZ)_3](NO_3)_2(CHZ=Carbohydrazide)

The molecular geometry,electronic structure,thermochemistry and infrared spectra of [Mg（CHZ）3]（ClO4）2 and [Mg（CHZ）3]（NO3）2 were comparatively studied using the Heyd-Scuseria-Ernzerhof（HSE） screened hybrid density functional with 6-31G＊＊ basis set.The experimental results show that the complexes have six-coordinated octahedron feature,and the metal-ligand interactions are predominantly ionic in nature.The calculated heats of formation predict that [Mg（CHZ）3]（NO3）2 is more stable than [Mg（CHZ）3]（ClO4）2.Detailed NBO analyses indicate that the ligand-anion interaction plays an important role in the stability for these two energetic complexes.Moreover,the stretching vibration frequencies of N-H bonds shift to lower wave number compared to the free CHZ ligand,which are caused by the delocalizations from N-H bond orbital to lone-pair electron antibond orbital of magnesium.

Discrete energetic(～50-200 keV) electron events in the high-altitude cusp/polar cap/lobe

We identified 28 discrete electron events(DEEs) with enhanced fluxes at ~50-200 keV in the high-altitude cusp/polar cap/lobe,using the electron measurements by the BeiDa Image Electron Spectrometer(BD-IES) instrument onboard an inclined(55°)geosynchronous orbit(IGSO) satellite from October 2015 to January 2016. We find that among the 28 DEEs, 22 occur in the nightside and mostly in the northern cusp/polar cap/lobe, while 6 occur in the dayside and all in the southern cusp; 24 events correspond to an average interplanetary magnetic field(IMF) component B_z>0, 3 correspond to an average IMF B_z<0, and 1 has no OMNI IMF data. In these DEEs, the observed average omnidirectional electron differential flux generally fits well to a power-law spectrum, J^E^(-γ), with the spectral index y ranging from 2.6 to 4.6, while the average electron flux varies over three orders of magnitude from event to event. The spectral index of these cusp DEEs are(strongly) larger than the spectral index of solar wind superhalo electrons(radiation belt electrons) observed by the WIND 3 D Plasma & Energetic Particle instrument(the BD-IES). At^110 keV,the electron flux of DEEs in the cusp/polar cap/lobe shows a weak positive correlation with the solar wind superhalo electron flux but no obvious correlation with the radiation belt electron flux. These results suggest that these DEEs probably originate from transient processes acting on the solar wind superhalo electrons, e.g., the mid/high-latitude reconnection.

Evolution of electron“zebra stripes”in the South Atlantic Anomaly:Initial observations from Macao Science Satellite-1

“Zebra stripes”denote banded structures characterized by periodic peaks and valleys in the spectrograms of energetic electrons in the Earth's inner radiation belt and slot region.In contrast to previous investigations primarily grounded in equatorial observations,this study presents two events exhibiting the evolution of electron zebra stripes within the South Atlantic Anomaly,as observed from the Macao Scientific Satellite-1 in low Earth orbit.Our findings affirm that the structural and evolutionary features of zebra stripes in both events accord with the drift echo hypothesis.The start time extrapolated from the electron spectrograms correlates with substorm onsets,consistent with prior conclusions.Notably,the duration of zebra stripe evolution during the event of June 5–6,2023,reaches an impressive 34.7 h,a markedly longer interval than findings from the Van Allen Probes.This discrepancy suggests that the observed lifetime of electron zebra stripes may not inherently reflect natural limitations but could be constrained by instrumental capabilities.The results implicate that high-energy-resolution detectors have the potential to significantly enhance our capacity to scrutinize the dynamics of the radiation belt.

Anti-proton contamination design of the imaging energetic electron spectrometer based on Geant4 simulation

The measurement of energetic particles plays an important role in the space environment monitoring and space weather forecasting.The accuracy of the energetic electron measurement is seriously influenced by the proton contamination.An anti-proton contamination design for the sensor of imaging energetic electron spectrometer is introduced in this paper.According to the electron and proton spectrum on the typical satellite orbits calculated by the radiation belt models,the efficiency of the anti-proton contamination design is estimated by the Geant4 simulation and the design is optimized based on the simulation results.

Energetic electron flux distribution model in the inner and middle magnetosphere

Based on the magnetospheric kinetic theory, a model is developed to specify the flux of energetic electrons in the inner and middle magnetosphere. Under the assumption of adiabatic motion and isotropic particle distribution maintained by pitch-angle scattering, the model calculates the electron flux by following bounce-averaged electric field, gradient, and curvature drift in the time dependent electric and magnetic field, meanwhile it counts the electron loss caused by pitch angle scattering. Using the model, the clectron flux distribution during a magnetic storm was calculated and compared with the observation data from the geosynchronous orbit. It is shown that the model can successfully reproduce most of the major electron flux enhancements observed at the geosynchronous orbit and generally tracks the satellite data well. The rms errors of the modeled logarithm of flux are between 0.5-1.0.

Multi-satellite observations on the storm-time enhancements of energetic outer zone electron fluxes driven by chorus waves

The evolution of energetic outer zone electron fluxes during the strong magnetic storm on September 28, 2002 is investigated based on the observations of SAMPEX and GOES-10 satellites. The observations of both satellites showed that energetic electron fluxes increased significantly during the storm recovery phase, and reached the maximum on October 6. The 1.5–14 MeV and 2.5–14 MeV electron fluxes observed by SAMPEX peaked around L=3.5 with values of 6×10 2 cm -2 s -1 sr -1 keV -1 and 5×10 3 cm -2 s -1 sr -1 keV -1 , which were about 10 and 8 times the pre-storm values. At the geostationary orbit, the >0.6 MeV and >2 MeV electron fluxes observed by GOES-10 showed enhancement up to 50 and 30 times. The plasma parameters and whistler-mode chorus waves in the outer radiation belt are also analyzed based on the data from Cluster C3 satellite. Cluster C3 satellite went through the outer radiation belt twice from 1 October to 4 October, and observed whistler-mode chorus waves with high intensity (10 -5 –10 -4 nT 2 Hz -1 ). Numerical calculations indicated that the observed chorus waves were in gyro-resonance with the radiation belt electrons. The current observations and calculations provide new evidence for that the gyro-resonance with chorus waves contribute significantly to the buildup of energetic outer zone electron fluxes during storms.

Responses of geostationary orbit energetic electron fluxes to chorus waves under different geomagnetic conditions

We investigate the flux evolution of geostationary orbit energetic electrons during a strong storm on 24 August 2005(event A,the storm index Dst<200 nT,the average substorm index AE=436 nT)and a weak storm on 28 October 2006(event B,Dst>50 nT,average AE=320 nT).Data collected by LANL and GOES-12 satellites show that energetic electron fluxes increase by a factor of 10 during the recovery phase compared to the prestorm level for both events A and B.As the substorm continued,the Cluster C4 satellite observed strong whistler-mode chorus waves(with spectral density approaching 10 5nT2/Hz).The wave amplitude correlates with the substorm AE index,but is less correlated with the storm Dst index.Using a Gaussian distribution fitting method,we solve the Fokker-Planck diffusion equation governing the wave-particle interaction.Numerical results demonstrate that chorus waves efficiently accelerate^1 MeV energetic electrons,particularly at high pitch angles.The calculated acceleration time scale and amplitude are comparable to observations.Our results provide new observational support for chorus-driven acceleration of radiation belt energetic electrons.

A cross-type imaging electron spectrometer

Energetic electron measurement is of great significance to theoretical space physics research and space weather applications.Current energetic electron detectors must cooperate with a spin-stabilized satellite platform to achieve high angular resolution in pitch angle distribution and three-dimensional(3D)imaging measurement of energetic electrons.This article introduces a cross-type quasi-3D imaging electron spectrometer(IES)based on pinhole imaging technology developed in the laboratory.The imager is composed of five imaging units,including a nine-pixel area array Si-PIN detector imaging unit in the middle and four three-pixel linear array Si-PIN detector imaging units placed in a cross-shape around it.The combination of five imaging units forms two orthogonal nine-pixel linear array detectors(with a common pixel in the middle).There are four pixels with a view angle of 20°×20°in the 45°oblique directions of the cross-type detection array.There are 21 imaging pixels in the entire crosstype sensor head,corresponding to 21 directions.Two multichannel integrated preamplifier ASICs are integrated in the sensor head to realize particle signal readout from 21 pixels.With a back-end electronics system,each pixel can achieve high energy resolution detection of 50–600 keV electrons.Radioactive sources and electron accelerators are used to calibrate the cross-type imaging sensor head,and the results demonstrate its good energy and directional detection characteristics(the energy resolution reaches 6.9 keV for the incident 200 keV electron beam).We performed simulations on the imaging sensor head’s ability to measure the electron pitch angle distribution on the three-axis stabilized platform,and the results show that the sensor head can perform quasi-three-dimensional detection of electrons incident within 2πsolid angles on the three-axis stabilized satellite platform,with an average angular resolution of the electron pitch angle distribution of less than 6°.

Magnetospheric chorus wave instability induced by relativistic Kappa-type distributions

We study the field-aligned propagating magnetospheric chorus wave instability using a fully relativistic wave growth formula,the previously developed relativistic Kappa-type(KT) distribution and the regular Kappa distribution of energetic electrons.We demonstrate that the peak growth rate using the nonrelativistic Kappa simulation is higher than that using either the relativistic KT or the Kappa simulation at/above 100 keV, because the significant relativistic effect yields a reduction in the relativistic anisotropy. The relativistic anisotropy Arel basically decreases as the thermal parameter θ2 increases, allowing the peak growth by relativistic KT or Kappa distribution to stay at the lower frequency region. The growth rates tend to increase with the loss-cone parameter l because the overall anisotropy increases. Moreover, at high energy ~1.0 MeV, both the growth rate and the upper cutoff frequency become smaller as l increases for the relativistic KT calculation because the significant relativistic effect reduces both the resonant anisotropy and the number of the hot electrons, which is in contrast to the relativistic and nonrelativistic Kappa distribution calculations because the less relativistic or non-relativistic effect enhances the resonant anisotropy as l increases. The above results can be applied to the whistler-mode wave instability in the outer radiation belts of the Earth, the Jovian inner magnetosphere and other astrophysical plasmas where relativistic electrons often exist.