Pitch Angle Distributions Research Articles

Numerical simulation of runaway electrons: 3-D effects on synchrotron radiation and impurity-based runaway current dissipation

Numerical simulations of runaway electrons (REs) with a particular emphasis on orbit dependent effects in 3-D magnetic fields are presented. The simulations were performed using the recently developed Kinetic Orbit Runaway electron Code (KORC) that computes the full-orbit relativistic dynamics in prescribed electric and magnetic fields including radiation damping and collisions. The two main problems of interest are synchrotron radiation and impurity-based RE dissipation. Synchrotron radiation is studied in axisymmetric fields and in 3-D magnetic configurations exhibiting magnetic islands and stochasticity. For passing particles in axisymmetric fields, neglecting orbit effects might underestimate or overestimate the total radiation power depending on the direction of the radial shift of the drift orbits. For trapped particles, the spatial distribution of synchrotron radiation exhibits localized “hot” spots at the tips of the banana orbits. In general, the radiation power per particle for trapped particles is higher than the power emitted by passing particles. The spatial distribution of synchrotron radiation in stochastic magnetic fields, obtained using the MHD code NIMROD, is strongly influenced by the presence of magnetic islands. 3-D magnetic fields also introduce a toroidal dependence on the synchrotron spectra, and neglecting orbit effects underestimates the total radiation power. In the presence of magnetic islands, the radiation damping of trapped particles is larger than the radiation damping of passing particles. Results modeling synchrotron emission by RE in DIII-D quiescent plasmas are also presented. The computation uses EFIT reconstructed magnetic fields and RE energy distributions fitted to the experimental measurements. Qualitative agreement is observed between the numerical simulations and the experiments for simplified RE pitch angle distributions. However, it is noted that to achieve quantitative agreement, it is necessary to use pitch angle distributions that depart from simplified 2-D Fokker-Planck equilibria. Finally, using the guiding center orbit model (KORC-GC), a preliminary study of pellet mitigated discharges in DIII-D is presented. The dependence of RE energy decay and current dissipation on initial energy and ionization levels of neon impurities is studied. The computed decay rates are within the range of experimental observations.

Pitch Angle Dependence of Energetic Electron Precipitation: Energy Deposition, Backscatter, and the Bounce Loss Cone

AbstractQuantifying radiation belt precipitation and its consequent atmospheric effects requires an accurate assessment of the pitch angle distribution of precipitating electrons, as well as knowledge of the dependence of the atmospheric deposition on that distribution. Here Monte Carlo simulations are used to investigate the effects of the incident electron energy and pitch angle on precipitation for bounce period time scales, and the implications for both the loss from the radiation belts and the deposition in the upper atmosphere. Simulations are conducted at discrete energies and pitch angles to assess the dependence on these parameters of the atmospheric energy deposition profiles and to estimate the backscattered particle distributions. We observe that the atmospheric response is both energy and pitch angle dependent. These effects together result in an energy‐dependent bounce loss cone angle, which can vary by 2–3° with particle energy when considered at low‐Earth orbit. This modeling also predicts that a significant fraction of the input electron distribution will be backscattered and should be observable by low‐Earth‐orbiting satellites as field‐aligned beams emerging from the atmosphere at energies lower than the input distribution and having pitch angles distributed just inside the loss cone.

Reply to Comment by Nishimura Et Al.

AbstractNishimura et al. (2010, https://doi.org/10.1126/science.1193186, 2011, https://doi.org/10.1029/2011JA016876, 2013, https://doi.org/10.1029/2012JA018242, and in their comment, hereafter called N18) have suggested that chorus waves interact with equatorial electrons to produce pulsating auroras. We agree that chorus can scatter electrons >10 keV, as do Time Domain Structures (TDSs). Lower‐energy electrons occurring in pulsating auroras cannot be produced by chorus, but such electrons are scattered and accelerated by TDS. TDSs often occur with chorus and have power in their spectra at chorus frequencies. Thus, the absence of power at low frequencies is not evidence that TDSs are absent, as an example shows. Through examination of equatorial electric field waveforms and electron pitch angle distributions measured on the Time History of Events and Macroscale Interactions during Substorms satellites (in place of examining field and particle spectra, as done by Nishimura et al.), we show that chorus cannot produce the field‐aligned electrons associated with pulsating auroras in the Nishimura et al. (2010, https://doi.org/10.1126/science.1193186) events, but TDSs can. Equatorial field‐aligned electron distributions associated with pulsating auroras and created by TDS in the absence of chorus or any other wave at the equator are also shown.

Toroidal Alfvén eigenmode triggered by trapped anisotropic energetic particles in a toroidal resistive plasma with free boundary

The toroidal Alfvén eigenmode (TAE), excited by trapped energetic particles (EPs), is numerically investigated in a tokamak plasma, using the non-perturbative magnetohydrodynamic-kinetic hybrid formulation based MARS-K code (Liu et al 2008 Phys. Plasmas 15 112503). Compared with the fixed boundary condition at the plasma edge, a free boundary enhances the critical value of the EPs kinetic contribution for driving the TAE. Free boundary also induces finite perturbations at the plasma edge as expected. An anisotropic distribution of EPs, in the particle pitch angle space, strongly enhances the instability and results in a more global mode structure, compared with the isotropic case. The plasma resistivity is also found to play a role in the EPs-destabilized TAE. In particular, the mode stability domain is mapped out, in the 2D parameter space of the plasma resistivity and a quantity defining the width of the particle distribution in pitch angle (for anisotropic distribution). A resonance layer in the poloidal mode structure, with the layer width increasing with the plasma resistivity, appears at the large width of the particle distribution in pitch angle space. A mode conversion, from the modified ideal kink by the EPs kinetic effect to the TAE, is also observed while increasing the birth energy of EPs. Computational results suggest that the TAE mode structure can be modified by certain key plasma parameters, such as the EPs kinetic contribution, the equilibrium pressure, the plasma resistivity, the distribution of EPs, as well as the birth energy of EPs. Such modification of the eigenmode structure can only be obtained following the non-perturbative hybrid approach (Wang et al 2013 Phys. Rev. Lett. 111 145003, Wang et al 2015 Phys. Plasmas 22 022509), as adopted in this study. More importantly, numerical results show that near the marginal stability point, the dominant poloidal harmonics of the TAE overlap with each other, and are localized at the tip positions of the Alfvén continua. This kind of TAE structure in high beta plasma with unstable ideal kink is substantially different from that of the conventional TAE.

Hydrodynamic modeling and experimental validation of a cycloidal propeller

In this paper, a lower-order unsteady hydrodynamic model of a cycloidal propeller along with in-house experiments to validate the model is presented. Towards this, the hydrodynamics of a cycloidal propeller is investigated thoroughly and various underlying physical phenomena such as dynamic virtual camber, effects of near and shed wake, leading-edge vortices are rigorously modeled. It is shown that the chord-wise variation of incidence velocity angle on cycloidal propeller blade is manifested as dynamic virtual camber, which depends on curvilinear flow geometry, pitch angle, pitch rate and inflow distribution. By including all these effects together, a generalized expression of additional lift due to virtual camber effect is developed. To capture the effects of near wake, a nonlinear lifting line model is incorporated. Rapid pitching of rotor blades produces unsteady phenomena such as strong leading-edge vortices and shed wakes. Polhamus leading-edge-suction analogy is applied to model leading-edge vortex. To capture the effects of shed wake, a method based on Theodorsen's approach is developed. A modified Double Multiple Streamtube (D-MS) model is used for modeling the complex inflow characteristics of a cycloidal propeller. The present hydrodynamic model is validated with measured time-history of forces obtained from in-house experiments at low Reynolds numbers.

Resonant Scattering of Radiation Belt Electrons by Off‐Equatorial Magnetosonic Waves

AbstractFast magnetosonic (MS) waves are commonly regarded as electromagnetic waves that are characteristically confined within ±3° of the geomagnetic equator. We report two typical off‐equatorial MS events observed by Van Allen Probes, that is, the 8 May 2014 event that occurred at the geomagnetic latitudes of 7.5°–9.2° both inside and outside the plasmasphere with the wave amplitude up to 590 pT and the 9 January 2014 event that occurred at the latitudes of—(15.7°–17.5°) outside the plasmasphere with a smaller amplitude about 81 pT. Detailed test particle simulations quantify the electron resonant scattering rates by the off‐equatorial MS waves to find that they can cause the pitch angle scattering and momentum diffusion of radiation belt electrons with equatorial pitch angles < ~75° or < ~58° (depending on the wave latitudinal coverage) on timescales of a day. Subsequent two‐dimensional Fokker‐Planck diffusion simulations indicate that the strong off‐equatorial MS waves are capable of efficiently transporting high pitch angle electrons to lower pitch angles to facilitate the formation of radiation belt electron butterfly distributions for a broad energy range from ~100 keV to >1 MeV within an hour. Our study clearly demonstrates that the presence of off‐equatorial MS waves, in addition to equatorial MS waves, can contribute importantly to the dynamical variations of radiation belt electron fluxes and their pitch angle distribution.

An Energetic Electron Flux Dropout Due to Magnetopause Shadowing on 1 June 2013

AbstractWe examine the mechanisms responsible for the dropout of energetic electron flux during 31 May to 1 June 2013 using Van Allen Probe (Radiation Belt Storm Probes (RBSP)) electron flux data and simulations with the Comprehensive Inner Magnetosphere‐Ionosphere (CIMI) model. During the storm main phase, L‐shells at RBSP locations are greater than ~8, which are connected to open drift shells. Consequently, diminished electron fluxes were observed over a wide range of energies. The combination of drift shell splitting, magnetopause shadowing, and drift loss all results in butterfly electron pitch angle distributions (PADs) at the nightside. During storm sudden commencement, RBSP observations display electron butterfly PADs over a wide range of energies. However, it is difficult to determine whether there are butterfly PADs during the storm main phase since the maximum observable equatorial pitch angle from RBSP is not larger than ~40° during this period. To investigate the causes of the dropout, the CIMI model is used as a global 4‐D kinetic inner magnetosphere model. The CIMI model reproduces the dropout with very similar timing and flux levels and PADs along the RBSP trajectory for 593 keV. Furthermore, the CIMI simulation shows butterfly PADs for 593 keV during the storm main phase. Based on comparison of observations and simulations, we suggest that the dropout during this event mainly results from magnetopause shadowing.

Nonlinear Wave‐Particle Interaction: Implications for Newborn Planetary and Backstreaming Proton Velocity Distribution Functions

AbstractSeen from the solar wind (SW) reference frame, the presence of newborn planetary protons upstream from the Martian and Venusian bow shocks and SW protons reflected from each of them constitutes two sources of nonthermal proton populations. In both cases, the resulting proton velocity distribution function is highly unstable and capable of giving rise to ultralow frequency quasi‐monochromatic electromagnetic plasma waves. When these instabilities take place, the resulting nonlinear waves are convected by the SW and interact with nonthermal protons located downstream from the wave generation region (upstream from the bow shock), playing a predominant role in their dynamics. To improve our understanding of these phenomena, we study the interaction between a charged particle and a large‐amplitude monochromatic circularly polarized electromagnetic wave propagating parallel to a background magnetic field, from first principles. We determine the number of fix points in velocity space, their stability, and their dependence on different wave‐particle parameters. Particularly, we determine the temporal evolution of a charged particle in the pitch angle‐gyrophase velocity plane under nominal conditions expected for backstreaming protons in planetary foreshocks and for newborn planetary protons in the upstream regions of Venus and Mars. In addition, the inclusion of wave ellipticity effects provides an explanation for pitch angle distributions of suprathermal protons observed at the Earth's foreshock, reported in previous studies. These analyses constitute a mean to evaluate if nonthermal proton velocity distribution functions observed at these plasma environments present signatures that can be understood in terms of nonlinear wave‐particle processes.

The Strongest Acceleration of >40 keV Electrons by ICME-driven Shocks at 1 au

Abstract We present two case studies of the in-situ electron acceleration during the 2000 February 11 shock and the 2004 July 22 shock, with the strongest electron flux enhancement at 40 keV across the shock, among all the quasi-perpendicular and quasi-parallel ICME-driven shocks observed by the WIND 3DP instrument from 1995 through 2014 at 1 au. We find that for this quasi-perpendicular (quasi-parallel) shock on 2000 February 11 (2004 July 22), the shocked electron differential fluxes at ∼0.4–50 keV in the downstream generally fit well to a double-power-law spectrum, J ∼ E −β , with an index of β ∼ 3.15 (4.0) at energies below a break at ∼3 keV (∼1 keV) and β ∼ 2.65 (2.6) at energies above. For both shock events, the downstream electron spectral indices appear to be similar for all pitch angles, which are significantly larger than the index prediction by diffusive shock acceleration. In addition, the downstream electron pitch-angle distributions show the anisotropic beams in the anti-sunward-traveling direction, while the ratio of the downstream over ambient fluxes appears to peak near 90° pitch angles, at all energies of ∼0.4–50 keV. These results suggest that in both shocks, shock drift acceleration likely plays an important role in accelerating electrons in situ at 1 au. Such ICME-driven shocks could contribute to the formation of solar wind halo electrons at energies ≲2 keV, as well as the production of solar wind superhalo electrons at energies ≳2 keV in interplanetary space.

Electron Acceleration by Dipolarization Fronts and Magnetic Reconnection: A Quantitative Comparison

Abstract Suprathermal electrons with energy from tens to hundreds of keV are frequently observed in the Earth's magnetotail. The generation of such electrons is typically attributed to magnetic reconnection, dipolarization fronts (DFs), or flux transport. However, which of these contributes more to this generation remains unclear. In this study, we quantitatively compare the electron acceleration by these processes, using the Cluster data. We analyze an event detected in the midtail and find that the suprathermal electrons there are first accelerated by magnetic reconnection and transported earthward, and then further accelerated locally at the DF. The acceleration process by reconnection and transport, resulting in an isotropic pitch angle distribution, contributes ∼70% to the total flux enhancement, while the acceleration process by the DF, resulting in a pancake distribution, contributes ∼30% to the flux enhancement. The electron acceleration at the DF is primarily attributed to a local betatron process that is successfully reproduced using an analytic model. In order to better understand this phenomenon, we examine an additional 16 similar events and find that the DFs and magnetic reconnection statistically contribute 11% ∼ 38% and 62% ∼ 89% to the total flux enhancement, respectively. This study greatly improves our understanding of the electron energization process in the magnetotail.

An Axial Hydro-Kinetic Turbine for Optimum Power Extraction using Tidal Dams

The present paper describes analytical optimization and numerical simulation of a modern hydro-kinetic turbine. It was a tidal turbine with twin elliptic-rotors. The turbines were installed within the twin ducts inside of a tidal dam. There was a gap between each of the turbines and the ducts for allowing vortex formation around each of turbines. The pitch angle distribution was optimized for highest energy extraction from water flow. The numerical simulations of the turbine have shown great power-coefficient that exceeds from 1.0 for tip-speed ratios greater than 3.5. According to power-coefficient curve, the runaway speed for the hydro-kinetic turbine was eliminated and the extracted power has increased with a second order function at higher tip-speed ratios. Based on obtained data, an axial hydro-kinetic turbine can not only absorb flow kinetic energy of incoming flow, but also can extract energy from parallel flows over each turbine. The power-coefficient curve against tip-speed ratio encounters with a break point around tip-speed ratio of 3.0. Simultaneously a strong vortex ring has formed around each of turbines. Flow trajectories illustrate how the hydro-kinetic turbine was able to absorb much more energy from external flows than conventional axial hydro-kinetic turbines.

Importance of electron distribution profiles to chorus wave driven evolution of Jovian radiation belt electrons

Wave-particle interactions triggered by whistler-mode chorus waves are an important contributor to the Jovian radiation belt electron dynamics. While the sensitivity of chorus-driven electron scattering to the ambient magnetospheric and wave parameters has been investigated, there is rather limited understanding regarding the extent to which the dynamic evolution of Jovian radiation belt electrons, under the impact of chorus wave scattering, depends on the electron distribution profiles. We adopt a group of reasonable initial conditions based upon the available observations and models for quantitative analyses. We find that inclusion of pitch angle variation in initial conditions can result in increased electron losses at lower pitch angles and substantially modify the pitch angle evolution profiles of > ~500 keV electrons, while variations of electron energy spectrum tend to modify the evolution primarily of 1 MeV and 5 MeV electrons. Our results explicitly demonstrate the importance to the radiation belt electron dynamics in the Jovian magnetosphere of the initial shape of the electron phase space density, and indicate the extent to which variations in electron energy spectrum and pitch angle distribution can contribute to the evolution of Jovian radiation belt electrons caused by chorus wave scattering.

Field‐Aligned Electrostatic Potentials Above the Martian Exobase From MGS Electron Reflectometry: Structure and Variability

AbstractField‐aligned electrostatic potentials in the Martian ionosphere play potentially important roles in maintaining current systems, driving atmospheric escape and producing aurora. The strength and polarity of the potential difference between the observation altitude and the exobase (~180 km) determine the energy dependence of electron pitch angle distributions (PADs) measured on open magnetic field lines (i.e. those connected both to the collisional atmosphere and to the interplanetary magnetic field). Here we derive and examine a data set of ~3.6 million measurements of the potential between 185 km and 400 km altitude from PADs measured by the Mars Global Surveyor Magnetometer/Electron Reflectometer experiment at 2 A.M./2 P.M. local time from May 1999 to November 2006. Potentials display significant variability, consistent with expected variable positive and negative divergences of the convection electric field in the highly variable and dynamic Martian plasma environment. However, superimposed on this variability are persistent patterns whereby potential magnitudes depend positively on crustal magnetic field strength, being close to zero where crustal fields are weak or nonexistent. Average potentials are typically positive near the center of topologically open crustal field regions where field lines are steeper, and negative near the edges of such regions where fields are shallower, near the boundaries with closed fields. This structure is less pronounced for higher solar wind pressures and (on the dayside) higher solar EUV irradiance. Its causes are uncertain at present but may be due to differential motion of electrons and ions in Mars's substantial but (compared to Earth) weak magnetic fields.

Spatial Distribution of Radiation Belt Protons Deduced from Solar Cell Degradation of the Arase Satellite

Analysis of solar-cell array panel (SAP) data from the Arase satellite orbiting in the inner magnetosphere showed a clear degradation of solar cells that could be attributed to trapped protons with energies greater than 6 MeV. Proton fluence was determined based on variations in the open-circuit voltage (Voc) of the solar cells, which we compared with that expected based on various distribution models (AP8MAX, AP9 mean and CRRESPRO quiet) of trapped protons. We found a general agreement, confirming the major contribution of trapped protons to the degradation, as well as a slight difference in the fluence expected based on the model calculations. To minimize this difference, we slightly modified the models, and found that concentrating the energetic protons on the magnetic equator provided a better agreement. Our results indicate that >6 MeV protons also has the equatorial concentration as reported for >18 MeV protons from the Van Allen Probes observation, and are interpreted as two components of the trapped protons, i.e., those of solar energetic particle (SEP) origin have an anisotropic pitch-angle distribution and are confined near the magnetic equator.

Scientific Objectives of Electron Losses and Fields INvestigation Onboard Lomonosov Satellite

The objective of the Electron Losses and Fields INvestigation on board the Lomonosov satellite (ELFIN-L) project is to determine the energy spectrum of precipitating energetic electrons and ions and, together with other polar-orbiting and equatorial missions, to better understand the mechanisms responsible for scattering these particles into the atmosphere. This mission will provide detailed measurements of the radiation environment at low altitudes. The 400–500 km sun-synchronous orbit of Lomonosov is ideal for observing electrons and ions precipitating into the atmosphere. This mission provides a unique opportunity to test the instruments. Similar suite of instruments will be flown in the future NSF- and NASA-supported spinning CubeSat ELFIN satellites which will augment current measurements by providing detailed information on pitch-angle distributions of precipitating and trapped particles.

Analytical forms of the first 14 moments of the cosmic ray Fokker–Planck equation

The Fokker–Planck transport equation describing the motion of energetic particles through a plasma is explored analytically. The latter equation provides a pitch-angle and position-dependent distribution function of the charged particles. In the current paper the first 14 moments of this equation are computed exactly for an arbitrary initial pitch angle. Such analytical forms are required in nonlinear treatments of perpendicular transport and other scenarios in plasma physics and astrophysics.

Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm.

During a magnetic storm on 23 June 2015, several very intense substorms took place, with signatures observed by multiple spacecraft including DMSP and Magnetospheric Multiscale (MMS). At the time of interest, DMSP F18 crossed inbound through a poleward expanding auroral bulge boundary at 23.5 h magnetic local time (MLT), while MMS was located duskward of 22 h MLT during an inward crossing of the expanding plasma sheet boundary. The two spacecraft observed a consistent set of signatures as they simultaneously crossed the reconnection separatrix layer during this very intense reconnection event. These include (1) energy dispersion of the energetic ions and electrons traveling earthward, accompanied with high electron energies in the vicinity of the separatrix; (2) energy dispersion of polar rain electrons, with a high‐energy cutoff; and (3) intense inward convection of the magnetic field lines at the MMS location. The high temporal resolution measurements by MMS provide unprecedented observations of the outermost electron boundary layer. We discuss the relevance of the energy dispersion of the electrons, and their pitch angle distribution, to the spatial and temporal evolution of the boundary layer. The results indicate that the underlying magnetotail magnetic reconnection process was an intrinsically impulsive and the active X‐line was located relatively close to the Earth, approximately at 16–18 RE.

Models of primary runaway electron distribution in the runaway vortex regime

A number of recent numerical calculations have shown the formation of a bump in runaway electron (RE) energy distribution by taking into account the synchrontron radiational damping force due to RE's gyromotions. Here, we present a detailed examination on how the bump location changes at different pitch-angles and the characteristics of the RE pitch-angle distribution. Although REs moving along the magnetic field are preferably accelerated and then populate the phase-space of larger pitch-angle mainly through diffusions, an off-axis (i.e., at finite pitch) peak can still form due to the presence of a runaway vortex that accumulates REs at a finite pitch-angle. A simplified Fokker–Planck model and its semi-analytical solutions based on local expansions around the O point are used to illustrate the characteristics of RE distribution around the O point of the runaway vortex in phase-space. The calculated energy location of the O point together with the local energy and pitch-angle distributions agree with the full numerical solution, confirming a previous empirical model for the runaway vortex location and explaining the off-axis peak in the distribution.

Modeling Particle Acceleration and Transport at a 2‐D CME‐Driven Shock

AbstractWe extend our earlier Particle Acceleration and Transport in the Heliosphere (PATH) model to study particle acceleration and transport at a coronal mass ejection (CME)‐driven shock. We model the propagation of a CME‐driven shock in the ecliptic plane using the ZEUS‐3D code from 20 solar radii to 2 AU. As in the previous PATH model, the initiation of the CME‐driven shock is simplified and modeled as a disturbance at the inner boundary. Different from the earlier PATH model, the disturbance is now longitudinally dependent. Particles are accelerated at the 2‐D shock via the diffusive shock acceleration mechanism. The acceleration depends on both the parallel and perpendicular diffusion coefficients κ|| and κ⊥ and is therefore shock‐obliquity dependent. Following the procedure used in Li, Shalchi, et al. (), we obtain the particle injection energy, the maximum energy, and the accelerated particle spectra at the shock front. Once accelerated, particles diffuse and convect in the shock complex. The diffusion and convection of these particles are treated using a refined 2‐D shell model in an approach similar to Zank et al. (). When particles escape from the shock, they propagate along and across the interplanetary magnetic field. The propagation is modeled using a focused transport equation with the addition of perpendicular diffusion. We solve the transport equation using a backward stochastic differential equation method where adiabatic cooling, focusing, pitch angle scattering, and cross‐field diffusion effects are all included. Time intensity profiles and instantaneous particle spectra as well as particle pitch angle distributions are shown for two example CME shocks.

Oxygen Ions O+ Energized by Kinetic Alfvén Eigenmode During Dipolarizations of Intense Substorms

AbstractSingly charged oxygen ions, O+, energized by kinetic Alfvén wave eigenmode (KAWE) in the plasma sheet boundary layer during dipolarizations of two intense substorms, 10:07 UT on 31 August 2004 and 18:24 UT on 14 September 2004, are investigated by Cluster spacecraft in the magnetotail. It is found that after the beginning of the expansion phase of substorms, O+ ions are clearly energized in the direction perpendicular to the magnetic field with energy larger than 1 keV in the near‐Earth plasma sheet during magnetic dipolarizations. The pitch angle distribution of these energetic O+ ions is significantly different from that of O+ ions with energy less than 1 keV before substorm onset that is in the quasi‐parallel direction along the magnetic field. The KAWE with the large perpendicular unipolar electric field, Ez ~ −20 mV/m, significantly accelerates O+ ions in the direction perpendicular to the background magnetic field. We present good evidences that O+ ion origin from the ionosphere along the magnetic field line in the northward lobe can be accelerated in the perpendicular direction during substorm dipolarizations. The change of the move direction of O+ ions is useful for O+ transferring from the lobe into the central plasma sheet in the magnetotail. Thus, KAWE can play an important role in O+ ion transfer process from the lobe into the plasma sheet during intense substorms.