Context . We use a global 3D hybrid plasma model to investigate the interaction between Mercury’s magnetosphere and the solar wind for the second BepiColombo swingby, evaluate magnetospheric regions, and study the typical energy profile of protons. Aims . The objective of this study is to gain a better understanding of solar wind entry and analyze simulated plasma data along a trajectory using BepiColombo swingby 2 conditions, with the goal of enhancing our comprehension of measurement data and potentially providing forecasts for future swingbys. Methods . To model Mercury’s plasma environment, we used the hybrid code AIKEF and developed a method to extract the particle (ion) data in order to compute the proton energy spectrum along the trajectory of BepiColombo during its second Mercury swingby on June 23, 2022. We evaluate magnetopause and bow shock stand-off distances under average upstream solar wind conditions with the Interplanetary Magnetic Field (IMF) condition derived from the BepiColombo magnetic field measurements during the second Mercury swingby. Results . We found that the magnetosheath on the quasi-perpendicular (dusk) side of the bow shock is thicker than that on the quasi-parallel (dawn) side, where a foreshock is formed. Multiple plasma populations can be extracted from our modeled energy spectra that assist in identifying magnetospheric regions. We observed protons of solar wind origin entering Mercury’s magnetosphere. Their energies range from a few electron volts in the magnetosphere up to 10 keV in the magnetosheath.

Upstream propagating waves are observed to correlate with the reflected ions in the foot of a high Mach number quasi-perpendicular collisionless shock. The respective wavefronts show time varying amplitude matching the variation of the reflected ions and the shock reformation cycles. We interpret this process in terms of the fast two-stream instability and investigate the results of the PIC simulation as compared with the prediction of the linear analysis. Evidence for upstream propagating whistler waves supported by two-stream instability is continuously growing, see for example, recent surveys based on MMS in-situ observations of the Earth bow-shock. The present study suggests that upstream propagating waves are consistent with and in particular supported by the mechanism of fast two-stream instability developing in the upstream region of the shock foot. By using particle-in-cell simulations, a highly non-stationary quasi-perpendicular collisionless shock exhibits reformation cycles characterized by extensions and compressions of the foot, ramp, and overshoot. Waves with upstream propagation are crossing the foot, with large variation of their phase velocities with respect to the rest frame of the shock, repeated periodically. Additionally, strong downstream propagating waves driven by incoming ions - incoming electrons two-stream instability (or slow two-stream instability) are observed close to the end of each shock cycle. In a system attached to the electron flow (regarded as proxy for the system used in the study of two-stream instabilities), the variations of the phase velocities appear to be significantly smaller. The linear theory based on dispersion analysis supports, in our case, the use of a 1-D code for exploring upstream whistler propagation driven by the fast two-stream instability, associated by former studies with 2-D configuration. At the same time, the analytical examination of the real part of the dispersion relation shows good agreement with the simulation results, while the imaginary part indicates a significant local growth rate of the fast two-stream instability, that can presumably compensate the otherwise strong damping of the oblique whistler waves. Fast two-stream instability excited in the foot of a collisionless shock by using 1-D PIC simulations Cyclic emissions of whistler waves in the foot of the shocks are supported by fast and slow two-stream instability Convergence of three independent approaches: simulations, analytical, and observations (MMS)

<p>The study of the structure and dynamics of Mercury’s magnetosphere is still an open research topic in space physics. Upon other mission objectives, the on-going BepiColombo mission will study the plasma environment around Mercury with multiple field and particle instruments. One of them is the Planetary Ion Camera (PICAM). It is an ion spectrometer designed to measure low-energy pick-up heavy ions (e.g. sodium). Due to ejection mechanisms and the solar wind influence, these particles are emitted from the surface of Mercury. The resulting electric currents, like perpendicular and field-aligned currents need to be studied to understand the global magnetospheric current structure as well as its variability due to the solar wind conditions.</p> <p>In this study, numerical simulations with a global 3D hybrid model are used to investigate and forecast the typical ion profile with energies up to 5 keV during the BepiColombo flyby trajectories in the years 2021-2025. Magnetotail reconnection causes the acceleration of particles towards the planet. The resulting field-aligned current is studied to about 3 R<sub>M</sub> in tailward direction. The simulations are conducted with the AIKEF (Adaptive Ion Kinetic Electron Fluid) model. The kinetic treatments of the ions will enable to directly compare magnetospheric particle species model results with PICAM observations.</p>

"The Multichannel Quantum Defect Theory and the Reduced R-Matrix are formally related and physically equivalent; both theories describe not only the internal dynamics but also the interactions in space of eliminated channels. One proves the Multichannel Quantum Defect Theory is Reduced Collision Matrix describing effect of eliminated channel on observed ones. The multichannel resonances originating in bound or quasistationary single particle states are described in terms of Reduced Collision Matrix. The single particle states are defined by Bound- or Quasistationary- State equation in the eliminated channel, relating channel logarithmic derivative to R-Matrix."

Collisionless dissipation of macroscopic energy into heat is an unsolved problem of space and astrophysical plasmas, e.g., solar wind and Earth's magnetosheath. The most viable process under consideration is the turbulent cascade of macroscopic energy to kinetic scales where collisionless plasma processes dissipate the energy. Space observations and numerical simulations show the formation of kinetic scale current sheets in turbulent plasmas. Instabilities in these current sheets (CS) can provide collisionless dissipation and influence the turbulence. Spatial gradients of physical quantities and non-Maxwellian velocity distribution functions provide the free energy sources for CS plasma instabilities. To determine the free energy sources provided by the spatial gradients of plasma density and electron/ion bulk velocities in CS formed in collisionless turbulent plasmas with an external magnetic field B (0), we carried out two-dimensional particle-in-cell-hybrid simulations and interpret the results within the limitations of the simulation model. We found that ion-scale CS in a collisionless turbulent plasma are formed primarily by electron shear flows, i.e., electron bulk velocity inside CS is much larger than ion bulk velocity while the density variations through the CS are relatively small (<10%). The electron bulk velocity and, thus, the current density inside the sheets are directed mainly parallel to B (0). The shear in the perpendicular electron and ion bulk velocities generates parallel electron and ion flow vorticities. Inside CS, parallel electron flow vorticity exceeds the parallel ion flow vorticity, changes sign around the CS centers, and peaks near the CS edges. An ion temperature anisotropy develops near CS during the CS formation. It has a positive correlation with the parallel ion and electron flow vorticities. Theoretical estimates support the simulation results.

Identification of a large-amplitude Alfvén wave decaying into a pair of ion-acoustic and daughter Alfvén waves is one of the major goals in the observational studies of space plasma nonlinearity. In this study, the decay instability is analytically evaluated in the 2-D wavenumber domain spanning the parallel and perpendicular directions to the mean magnetic field. The growth-rate determination of the density perturbations is based on the Hall MHD (magnetohydrodynamic) wave–wave coupling theory for circularly polarized Alfvén waves. The diagrams of the growth rates versus the wavenumber and propagation angle derived in analytical studies are replaced by 2-D wavenumber distributions and compared with the corresponding wavevector spectrum of density and magnetic field fluctuations. The actual study reveals a perpendicular spectral pattern consistent with the result of a previous study based on 3-D hybrid numerical simulations. The wavevector signature of the decay instability observed in the two-dimensional wavenumber domain ceases at values of plasma beta larger than β=0.1. Growth-rate maps serve as a useful tool for predictions of the wavevector spectrum of density or magnetic field fluctuations in various scenarios for the wave–wave coupling processes developing at different stages in space plasma turbulence.

Here we evaluate for the first time the growth rate of the decay instability in the 2-D wavevector domain spanning the parallel and perpendicular directions to the mean magnetic field. The growth rate is computed for the density perturbations based on the Hall MHD wave-wave coupling theory, which serves as a proxy for the energy spectrum of the compressive magnetic field fluctuations. The growth rate is then also determined for the daughter waves by considering the conservation of the frequencies and the wavevectors for the wave transmission (additive wave-wave coupling) and the wave reflection (subtractive wave-wave coupling). The visualized growth rate is helpful in evaluating the maximum propagation angle to which the decay instability (of the parallel propagating pump Alfven wave) operates.

Nonlinearities in space and astrophysical plasmas generate a set of magnetic filaments or bundles that have an incompressible sense of fluctuations and propagate highly obliquely to the mean magnetic field. Those filaments are caused by wave–wave interactions in which a large-amplitude Alfvén wave (or pump Alfvén wave) is disturbed by thermal, density fluctuations and collapses into obliquely propagating Alfvén waves at shorter wavelengths than the pump. Hybrid simulations confirm the filament excitations in the three-dimensional low-beta plasma. Alfvén waves develop into magnetic filaments on a time scale of about 300 ion gyrations. The filaments grow in a multi-channel way at various azimuthal angles around the mean magnetic field.

Three-dimensional hybrid simulations have been carried out to verify the hypothesis of simultaneous multi-channel decay of a large-amplitude Alfvén wave in a low-beta plasma, e.g., in the shock-upstream region or the solar corona. Obliquely propagating daughter modes are excited along the perpendicular direction to the mean magnetic field at the same parallel wavenumbers and frequencies as the daughter modes driven by the field-aligned decay. We find that the transversal spectrum of waves is controlled by the multi-channel coupling of the decay process in low-beta plasmas and originates in the dispersion state of the shear Alfvén wave.

Abstract. By means of hybrid simulations, we present a study on plasma heating by the field-aligned parametric decay of a monochromatic left-handed polarized Alfven wave. Simultaneous multidimensional comparisons of the wave modes and proton kinetics suggest that parametric decay of Alfven waves and pitch angle scattering of solar wind protons are interrelated. Parametric decay mechanism yields counter-propagating Alfven waves that can shape and broaden via pitch angle scattering mechanism both the sunward and antisunward sides of the proton velocity distribution functions in agreement with in situ measurements of fast stream solar wind plasmas.

The Siegert states are approached in the framework of Bloch–Lane–Robson theory of quantum collisions. Both the bound and the quasi-stationary Siegert states are subject of the equation relating the channel R-matrix element to the logarithmic derivative. The Siegert state dependence on the decay channel parameters results in channel renormalization of reduced widths, especially near threshold. The neutron subthreshold and the electron Rydberg states are examples of subthreshold Siegert states. The Siegert approach results in Heisenberg’s S-matrix formula for the bound state and the subthreshold resonance. The Siegert state residue is a spectroscopic asymptotic normalization constant. The decay width of the electron Rydberg channel resonance is, up to a factor, the electron strength function.

By three-dimensional hybrid simulations, proton heating is investigated starting from a monochromatic large-amplitude Alfvén wave with left-handed circular polarization launched along the mean magnetic field in a low-beta plasma. We find that the perpendicular scattering is efficient in three dimensions and the protons are heated by the obliquely propagating waves. The thermal core proton population is heated in three dimensions as well in the longitudinal and parallel directions by the field-aligned and obliquely propagating sound waves out of the parametric decay. The astrophysical context is discussed.

AbstractRecently, Comişel et al. (2015) suggested an adaptation of the deHoffmann‐Teller (HT) frame, to take into account the magnetic field fluctuations observed nearby and inside a quasi‐perpendicular collisionless shock. Such fluctuations can be quite large, making the standard HT frame unsuitable for studies of the electric field, cross‐shock potential, and electron energy gain. While the HT frame is appropriate to cancel the motional electric field for steady state shocks, a similar effect is achieved with the adaptive HT (AHT) frame under time varying conditions, albeit by a local rather than global transformation. The sliding AHT motion parallel to the shock surface changes from point to point and time to time, unlike the regular motion of the HT frame. On the other hand, in both cases the electric field at each point is normal to the 1‐D shock and its integral across the shock is equal to the integral of the parallel electric field along the magnetic field line. In this paper we elaborate the concept of the AHT frame, illustrate it with a 1‐D simulation, and point out the association of magnetic field fluctuations with electron phase space structures, apparently related to electron trapping by dispersive whistler waves in the foot of the shock. The AHT frame may help assessing the relative weight of nonstationarity at shocks and other MHD discontinuities, by simulated and observed data, under various plasma regimes.

Continuous Position Sensitive Diamond Detector (CPSDD) development started by using the single crystal (sc) diamond material. The intrinsic high detection efficiency of sc diamond, providing a high Signal to Noise (S/N) ratio, allowed the full testing of CPSDD with alpha-particles. However, due to the size limitations of sc diamond, the development of Large Area CPSDD (LACPSDD) naturally evolved towards the use of polycrystalline (pc) diamond material, produced by chemical vapor deposition (CVD). The charge generated by the particle or radiation impact is collected through diamond like carbon (DLC) layers and associated metallic electrodes deposited on the sides of the pc diamond plate. The incident particle position can be obtained via charge division measurement by using charge sensitive amplifiers (CSA) connected to each electrode. In this paper we report the improvement in LACPSDD design by showing results obtained for two pc diamond detector (pcDD) structures. The first pcDD has a DLC layer with four electrodes at the corners of the front side, whereas the back side is fully metallized. The second pcDD has DLC layers on both sides of the detector plate, each equipped with two parallel electrode strips, along the x and y axis, respectively. Experimental results on the first pcDD showed an ion rate limitation, caused by the increase in the detector time constant (because of the larger detection area), and a low S/N ratio, due to the specific reduced signal associated with low Charge Collection Efficiency (CCE) of pc diamond. Subsequently, by using an optimized electronics and a better pc diamond (higher CCE), the second pcDD shows a higher S/N ratio, as well as a lower time constant. This paper presents simulation results on the time constant and an analytical evaluation of the S/N ratio, which serve to optimize the pc LACPSDDs. We also show experimental test results with alpha-particles, as well as Ni-54 (1.7 AGeV) and C-12 (11.4 AMeV) ion beams.Prime Novelty Statement: This paper presents the first large area continuous position sensitive diamond detectors implemented on polycrystalline CVD diamond material for single ionizing particle detection. (C) 2016 Elsevier B.V. All rights reserved.

Collisionless shock waves in space and astrophysical plasmas can accelerate electrons along the shock layer by an electrostatic potential, and scatter or reflect electrons back to the upstream region by the amplified magnetic field or turbulent fluctuations. The notion of the critical pitch angle is introduced for non-adiabatic electron acceleration by balancing the two timescales under a quasi-perpendicular shock wave geometry in which the upstream magnetic field is nearly perpendicular to the shock layer normal direction. An analytic expression of the critical pitch angle is obtained as a function of the electron velocity parallel to the magnetic field, the ratio of the electron gyro- to plasma frequency, the cross-shock potential, the width of the shock transition layer, and the shock angle (which is the angle between the upstream magnetic field and the shock normal direction). For typical non-relativistic solar system applications, the critical pitch angle is predicted to be about 10°. An efficient acceleration is expected below the critical pitch angle.

Four-dimensional energy spectra and a diagram for dispersion relations are determined for the first time in a magnetic reconnection region in the magnetotail using data from four-spacecraft measurements by the Cluster mission on a spatial scale of 200 km, about 0.1 ion inertial lengths. The energy spectra are anisotropic with an extension in the perpendicular direction and axially asymmetric with respect to the mean magnetic field. The dispersion diagram in the plasma rest frame is in reasonably good agreement with the ion Bernstein waves at the second and higher harmonics of the proton gyrofrequency. Perpendicular-propagating ion Bernstein waves likely exist in an outflow region of magnetic reconnection, which may contribute to bifurcation of the current sheet in the outflow region.