Growth Of Plasma Waves Research Articles

Fast nonlinear scattering of runaway electron beams through resonant interactions with plasma waves

Abstract The resonant interaction between a runaway electron (RE) beam and a reactor-grade background plasma is investigated through two-dimensional particle-in-cell simulations, employing a simplified model of the system. The temporal evolutions of the electron momentum distribution function for two separate initial beam energies (1 and 10 MeV) are tracked, revealing the occurrence of plasma wave growth concomitant with pitch angle scattering or momentum distribution diffusion within the RE beam. Notably, we identify and confirm the dependence of the dominant resonance condition on the initial kinetic energy of the RE beam. Furthermore, we quantify the effect of particle-wave interactions on the RE momentum distribution diffusion by assessing the average kinetic energy flux from the RE distribution function.

PINE-RT: An operational real-time plasmasphere model

The plasmasphere is a region of cold and dense plasma around the Earth, corotating with the Earth. Its plasma density is very dynamic under the influence of the solar wind and it influences several processes such as the GPS navigation, the surface charging of the satellites and the propagation and growth of plasma waves. In this manuscript, we present a new machine-learning model of the equatorial plasma density depending only on the Kp index and the solar-wind properties at the L1 Lagrange point. We call this model PINE-RT as it has been inspired by the recently-introduced PINE (Plasma density in the Inner magnetosphere Neural network-based Empirical) model and it has been developed to run in real-time (RT) in the context of the PAGER project. This project is an EU Horizon 2020 project aiming at forecasting the threats of satellite charging as a consequence of the solar activity 1–2 days ahead. In PAGER, the Kp index and the solar-wind properties at L1 are the inputs which are made available for the plasmasphere modeling. We report here the detailed derivation of the PINE-RT model and its validation and comparison with two state-of-the-art machine-learning and physics-based models. The model is currently running in real-time and its predictions are publicly available.

Rocket‐Released Neutral Clouds in the Ionosphere: Formation, Evolution, and Detection

AbstractReleasing diffuse artificial clouds into the space environment using a rocket or spacecraft can modify the natural plasma state. This uses space itself as a laboratory for studying plasma phenomena that cannot be reproduced on the ground. The Space Measurement of A Rocket‐released Turbulence (SMART) mission will inject a beam of barium neutral vapor into the ionosphere and perpendicular to the Earth's magnetic field. Barium atoms will be photoionized, forming an ion ring distribution that is unstable to lower hybrid waves. Large amplitude lower hybrid waves nonlinearly scatter to whistler and magnetosonic waves that can propagate out to the magnetosphere. This paper details the theory, modeling, and simulation we used to design this release experiment to optimize the energy in the plasma waves under a variety of constraints. A product of this analysis is quantitative predictions for some in situ and remote measurements. Hydrocode simulations of barium vapourization and acceleration via shaped charge provide the initial state of the neutral beam. We optimize the apogee, orientation, and position of the payload and instruments. Cloud dynamics are simulated with a direct simulation Monte Carlo technique, which includes photoionization with metastable barium states, collisions with the neutral background atmosphere, optical line emission, gravity, and electromagnetic forces. We predict the plasma density measured by the instrument payload and the remotely measured optical intensity. We also examine how the plasma wave growth differs at the measurement location compared to the bulk of the barium cloud.

Theory of magnetic turbulence and shock formation induced by a collisionless plasma instability

Magnetic fields are ubiquitous in universe, space, and laboratory plasmas. Especially, self-generated magnetic fields are important to know the mind of nature. The formation of Weibel-mediated collisionless shock is studied theoretically as a structure formation by the linear plasma wave growth, nonlinear saturation, and mode–mode coupling. Following a series of computer simulations and experimental studies of the physics, a simple model equation is proposed here to describe the time evolution of magnetic turbulence. Weibel instability is saturated by magnetic pressure, and thicker filaments continue to be generated by current coalescence (magnetic reconnection) mechanism. The model equation concludes the fact that the filament spacing increases linearly in time, and the magnetic energy power spectrum is given as Bk2 ∝ k−2. The time evolution of the turbulence is characterized with the cascade toward smaller k. Such inverse cascade is well-known in 2D hydrodynamic turbulence such as a typhoon or hurricane formation and is known to have Kolmogorov spectrum k−5/3. Although only a small difference in power, the physics of inverse cascades is very different as shown in the present paper. With use of Alfvén current limit condition, the criteria of collisionless shock formation are evaluated. The present theory is compared to corresponding experiments done with Omega and NIF lasers and a variety of PIC simulations. The theory is also applied to evaluate the strength of magnetic field near the shock front of the supernova remnant SN1006. The enhancement of magnetic field of about 25 μG is concluded in the present theory. Finally, a universality of the model equation is shown by applying the theory to the turbulent mixing due to Rayleigh–Taylor instability at the contact surface of two fluids in a gravitational or inertial force, which is very important in compressing plasma such as inertial confinement fusion by implosion. It is shown that the well-known evolution physics, mixing layer of the two fluids grows in proportion to (time)2, can be explained with the same model equation.

Growth of plasma waves of scales longer than 10 km by gradient-drift instability in the E-region of equatorial ionosphere

In this study, a linear analysis of the Gradient Drift Instability (GDI) applicable for horizontal wavelengths longer than 10 km in the E region is presented. By analytically solving the non-local differential equation for the polarization potential, analytical forms of the dispersion relation and growth rate, hosting new contributions from non-local effects, are obtained. The new growth rate and the amplitude of polarization potential are examined for a wide range of wavelengths that reveal the positive growth of GDI for wavelengths of ∼25 km. These characteristics raise the possibility of the formation of unstable structures of vertical size ∼20–30 km in the upper E region, often observed during twilight hours.

Source region and growth analysis of narrowband Z‐mode emission at Saturn

AbstractIntense Z‐mode emission is observed in the lower density region near the inner edge of the Enceladus torus at Saturn, where these waves may resonate with MeV electrons. The source mechanism of this emission, which is narrow‐banded and most intense near 5 kHz, is not well understood. We survey the Cassini Radio and Plasma Wave Science data to isolate several probable source regions near the inner edge of the Enceladus density torus. Electron phase space distributions are obtained from the Cassini Electron Spectrometer, part of the Cassini Plasma Spectrometer investigation. We perform a plasma wave growth analysis to conclude that an electron temperature anisotropy and possibly a weak loss cone can drive the Z mode as observed. Electrostatic electron acoustic waves and perhaps weak beam modes are also found to be unstable coincident with the Z mode. Quasi‐steady conditions near the Enceladus density torus may result in the observations of narrowband Z‐mode emission at Saturn.

Coincident multi-point observations of the E- and F-region decametre-scale plasma waves at high latitudes

Presented is an extensive analysis of the E-region backscatter observed at magnetic latitudes 75°–80°N by the PolarDARN component of the Super Dual Auroral Radar Network (SuperDARN). The statistical occurrence characteristics of the short-range echoes reveal significant differences from those of the auroral and sub-auroral SuperDARN radars. In particular, most backscatter is detected in the midnight sector in the closest range gates where the geometric magnetic aspect angles are in excess of 10° where no backscatter is normally expected. One explanation offered is that intense ionisation layers significantly refract the radar waves allowing a regular detection of the backscatter from the nearest range gates. A statistical analysis of the spectral echo types within the PolarDARN dataset showed strong similarities with the auroral SuperDARN radars, despite significant differences in the geometric aspect angle coverage. The low-velocity echoes dominated the datasets, while the high-velocity echoes were observed rather sporadically in the morning sector. The location of the PolarDARN radars relative to the more-equatorward SuperDARN radars facilitates the use of a new experimental setup that has coincident and simultaneous HF radar coverage of the E and F regions on the same magnetic field lines. Using this configuration, the SuperDARN plasma flow measurements are employed to investigate the E-region phase velocity dependence on the electric field strength and the flow angle at multiple locations. By employing elevation angle estimates, a marked decrease in the normalised phase velocity with decreasing altitude is observed, which provides direct support to the previously suggested collisional depression of the irregularity phase velocity. It is also shown that the normalised phase velocity is smaller for higher electric fields, which is interpreted as being due to a change in the contribution of the convective effects to the plasma wave growth at decametre scales.

Ion cyclotron harmonics in the Saturn downward current auroral region

[1] Observations of intense upgoing electron beams and diffuse ion beams have been reported during a pass by Cassini in a downward current auroral region, nearby a source region of Saturn kilometric radiation. Using the Cassini Radio and Plasma Wave Science (RPWS) instrument low frequency waveform receiver and the Cassini Plasma Spectrometer Investigation (CAPS) instrument we have been able to identify ion cyclotron harmonic waves associated with the particle beams. These observations indicate similarities with terrestrial auroral emissions, and may be a source of wave-particle interactions. We fit the observed plasma electron distribution with drifting Maxwellians and perform a linear numerical analysis of plasma wave growth. The results are relevant to ion heating and possibly to electron acceleration.

Mechanisms of ionospheric mass escape

The dependence of ionospheric O+ escape flux on electromagnetic energy flux and electron precipitation into the ionosphere is derived for a hypothetical ambipolar pickup process, powered the relative motion of plasmas and neutral upper atmosphere, and by electron precipitation, at heights where the ions are magnetized but influenced by photo‐ionization, collisions with gas atoms, ambipolar and centrifugal acceleration. Ion pickup by the convection electric field produces “ring‐beam” or toroidal velocity distributions, as inferred from direct plasma measurements, from observations of the associated waves, and from the spectra of incoherent radar echoes. Ring beams are unstable to plasma wave growth, resulting in rapid relaxation via transverse velocity diffusion, into transversely accelerated ion populations. Ion escape is substantially facilitated by the ambipolar potential, but is only weakly affected by centrifugal acceleration. If, as cited simulations suggest, ion ring beams relax into nonthermal velocity distributions with characteristic speed equal to the local ion‐neutral flow speed, a generalized “Jeans escape” calculation shows that the escape flux of ionospheric O+ increases with Poynting flux and with precipitating electron density in rough agreement with observations.

A statistical study of the spatial distribution of Co‐operative UK Twin Located Auroral Sounding System (CUTLASS) backscatter power during EISCAT heater beam‐sweeping experiments

High‐power electromagnetic waves can excite a variety of plasma instabilities in Earth's ionosphere. These lead to the growth of plasma waves and plasma density irregularities within the heated volume, including patches of small‐scale field‐aligned electron density irregularities. This paper reports a statistical study of intensity distributions in patches of these irregularities excited by the European Incoherent Scatter (EISCAT) heater during beam‐sweeping experiments. The irregularities were detected by the Co‐operative UK Twin Located Auroral Sounding System (CUTLASS) coherent scatter radar located in Finland. During these experiments the heater beam direction is steadily changed from northward to southward pointing. Comparisons are made between statistical parameters of CUTLASS backscatter power distributions and modeled heater beam power distributions provided by the EZNEC version 4 software. In general, good agreement between the statistical parameters and the modeled beam is observed, clearly indicating the direct causal connection between the heater beam and the irregularities, despite the sometimes seemingly unpredictable nature of unaveraged results. The results also give compelling evidence in support of the upper hybrid theory of irregularity excitation.

Toward a theory of the double plasma resonance in the solar corona

Specific features of the double plasma resonance effect in a magnetized plasma of the solar corona are discussed. The effect consists in enhanced generation of plasma waves in the regions where the upper hybrid frequency coincides with electron gyrofrequency harmonics. It is widely used for interpretation of a fine structure in solar radio emission spectrum in the form of parallel drifting quasi-harmonic stripes of enhanced radiation intensity (zebra pattern). It is shown that the plasma-wave growth rate increases due to both dispersion properties of plasma waves, which are determined by the equilibrium plasma component, and electrons which are non-equilibrium with respect to the velocities transverse to the magnetic field. Special attention is given to an incorrect consideration of the double plasma resonance effect in some papers.

Transit‐time mechanism of plasma instability in high electron mobility transistors

AbstractWe show that the transit‐time effects in the high‐electric‐field region near the drain edge of the channel of a field effect transistor can increase the increment of plasma wave growth in the device channel. These electron transit‐time effects might lead to the plasma wave instability in high‐electron‐mobility transistors (HEMTs) in the terahertz range of frequencies. We demonstrate that the self‐excitation of plasma oscillations is possible when the ratio of the electron velocity in the high field region, ud, and the gate length, Lg, is sufficiently large in comparison with the electron collision frequency in the gated channel, ν, i.e udLg > ν/k, where k is a constant. Hence, in contrast with the Dyakonov–Shur mechanism of plasma instability in HEMTs, the plasma instability associated with the mechanism under consideration can occur at fairly low values of the electron mobility in the gated portion of the HEMT channel. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

On the Magnetic Fields and Particle Acceleration in Cassiopeia A

We investigate the nonthermal X-ray emission from Cas A, using BeppoSAX, Compton Gamma Ray Observatory OSSE, and Chandra data. For the hard X-ray continuum we test the model proposed by Laming, which invokes nonthermal bremsstrahlung from electrons accelerated by lower hybrid plasma waves. The justification for this model comes from our determination of a lower limit to the average magnetic field of B > 0.5 mG. For such high magnetic fields, the synchrotron losses are severe enough that most of the electron populations responsible for the radio emission have maximum electron energies well below the limit for which X-ray synchrotron emission is important. However, we do suggest that the rim surrounding Cas A, seen in Chandra continuum images, is X-ray synchrotron emission. The width of this rim of 15-4'' can be used to infer the magnetic field near the shock front, for which we estimate B = 0.08-0.16 mG and electron energies of ~57-40 TeV. This magnetic field strength is lower than the average magnetic field but higher than what may be expected from shocked interstellar medium, suggesting either a high magnetic field in the wind of the progenitor or rapid postshock field amplification by nonlinear growth of plasma waves. Combining the two magnetic field measurements, we have constructed a simple two-zone model. Most of the radio emission comes from inside Cas A, where the magnetic field is strong. In contrast, the inverse Compton emission is dominated by emission from near the shock front. Only for our lower limit on the magnetic field strength near the shock front is it possible to explain the recent detection of TeV emission by the High Energy Gamma Ray Astronomy experiment with inverse Compton emission, for which, in addition, we have to assume a rather high far-infrared photon density that should be twice as high as our best estimate of ~70 cm-3. Pion decay is therefore likely to be the dominant emission from Cas A at TeV energies.

Auroral zone dayside precipitation during magnetic storm initial phases

Significant charged-particle precipitation occurs in the dayside auroral zone during and after interplanetary shock impingements on the Earth's magnetosphere. The precipitation intensities and spatial and temporal evolution are discussed. Although the post-shock energy flux (10– 20 erg cm −2 s −1 ) is lower than that of substorms, the total energy deposition rate may be considerably greater (∼ an order of magnitude) than nightside energy rates due to the greater area of the dayside portion of the auroral oval (defined as extending from 03 MLT through noon to 21 MLT). This dayside precipitation represents direct solar wind energy input into the magnetosphere/ionosphere system. The exact mechanisms for particle energization and precipitation into the ionosphere are not known at this time. Different mechanisms are probably occurring during different portions of the storm initial phase. Immediately after shock compression of the magnetosphere, possible precipitation-related mechanisms are: (1) betatron compression of preexisting outer zone magnetospheric particles. The anisotropic plasma is unstable to loss-cone instabilities, leading to plasma wave growth, resonant particle pitch-angle scattering and electron and proton losses into the upper ionosphere. (2) The compression of the magnetosphere can also lead to enhanced field-aligned currents and the formation of dayside double-layers. Finally (3) in the latter stages of the storm initial phase, there is evidence for a long-lasting viscous-like interaction occurring on the flanks of the magnetopause. Ground-based observations identifying the types of dayside auroral forms would be extremely useful in identifying the specific solar wind energy transfer mechanisms.

Evolution to turbulence in a capacitor model of resonance absorption

The interaction of a powerful, subpicosecond laser pulse with plasma is modeled within the capacitor model by means of one-dimensional electrostatic particle code. The temporal profile of the laser pulse and the growth of the electron energy by several orders of magnitude were taken into account providing adequate temporal and spatial resolution. It is shown that initially, a coherent structure is excited, and growth of plasma waves results in wave breaking and acceleration of electrons followed with decreasing intervals between them, accelerating electrons in both directions. Finally the system evolves to a state of moderate Langmuir turbulence where E2/(16πnT)≪1 due to the strong heating of plasma electrons and the decrease of excited plasma wave fields.

Effects of Coulomb collisions on cyclotron maser and plasma wave growth in magnetic loops

The evolution of nonthermal electrons accelerated in magnetic loops is determined by solving the kinetic equation, including magnetic field convergence and Coulomb collisions in order to determine the effects of these interactions on the induced cyclotron maser and plasma wave growth. It is found that the growth rates are larger and the possibility of cyclotron maser action is stronger for smaller loop column density, for larger magnetic field convergence, for a more isotropic injected electron pitch angle distribution, and for more impulsive acceleration. For modest values of the column density in the coronal portion of a flaring loop, the growth rates of instabilities are significantly reduced, and the reduction is much larger for the cyclotron modes than for the plasma wave modes. The rapid decrease in the growth rates with increasing loop column density suggests that, in flare loops when such phenomena occur, the densities are lower than commonly accepted.

A Microwave-Driven Beat Wave Accelerator for Scaled Experments

It is shown that large-amplitude (~ 104 V/cm) plasma waves can be resonantly excited by beating microwave pumps in an open resonator filled with plasma of subcritical density. The advantages and the possibilities of scaled experiments on beat wave accelerator concepts are discussed, in particular the plasma wave growth and saturation and the role of competing instabilities.

Processes in the Magnetotail Neutral Sheet

This paper reviews neutral sheet observations and theories emphasizing particle acceleration or "inertial dissipation". The existence of the central current sheet and cross-tail electric field in the magnetotail neutral sheet implies an energy dissipation which is roughly a few percent of the incident solar wind power on the entire magnetosphere. This is an important - if not the dominant - energy dissipation in the magnetosphere. Earthward streaming ions in the plasma sheet boundary layer can result from simple single particle acceleration in the current sheet and these beams carry sufficient energy to account for this dissipation. Although stochastic processes need not be invoked, "inertial conductivity" is inferred from the time the particles spend undergoing acceleration within the current sheet. The particle motion thus leads to simple consistency "equilibrium states" and the motion has been used as the basis of an explosive reconnection model by Coroniti. Finally, observations and theories of broadband electrostatic noise, which may also provide dissipation, are reviewed. Particle distributions which result from neutral sheet energization will likely be unstable to the growth of plasma waves. Broadband electrostatic noise is the most intense and frequently occurring plasma wave mode in the magnetotail and the intensity is observed to peak in the plasma sheet boundary layer. It is thought to be excited by the ion beam acoustic instability. Resonant heating of plasma sheet boundary layer ions may be responsible for the hot ion component of the central plasma sheet.

Laser beat-wave accelerator and plasma noise.

Plasma noise effects on the beat-wave resonance condition and the subsequent reduction of the accelerating electric field for the laser beat-wave accelerator are investigated. Plasma noise or turbulence causes the accelerating electric field to saturate at a reduced level \ensuremath{\epsilon}=${L}_{\mathrm{eff}/\mathrm{L}}$ of the ideal coherent accelerating field, where ${L}_{\mathrm{eff}}$ is the effective growth length for the plasma wave and L is the ideal growth length. When the noise parameter \ensuremath{\sigma}=〈(\ensuremath{\delta}n${)}^{2}$〉/${n}^{2}$ is above a threshold value, we find ${L}_{\mathrm{eff}\mathrm{\ensuremath{\simeq}}2\mathrm{c}/{\ensuremath{\omega}}_{p}^{2}{\ensuremath{\tau}}_{c}\mathrm{\ensuremath{\sigma}}}$, where ${\ensuremath{\tau}}_{c}$ is the correlation time of the noise spectrum along \ensuremath{\omega}=${\mathrm{kv}}_{p}$. Slower noise is less effective in limiting the plasma wave growth. For strong noise ${L}_{\mathrm{eff}}$ becomes shortened to the correlation length in the noise ${L}_{c}$=${v}_{p}$${\ensuremath{\tau}}_{c}$. In the case of slowly increasing mismatch in the beat-wave resonance condition, the effective growth length ${L}_{\mathrm{eff}}$ becomes the geometric mean of the density gradient scale length ${L}_{n}$ and the collisionless skin depth (${L}_{n}$c/${\ensuremath{\omega}}_{p}$${)}^{1/2}$. .AE

Collisionless Effects on Beam-Return Current Systems in Solar Flares

A large fraction of the electrons which are accelerated during the impulsive phase of solar flares stream towards the chromosphere and are unstable to the growth of plasma waves. The linear and nonlinear evolution of plasma waves as a function of time is analyzed with the use of a set of rate equations that follow in time the non-linearly coupled system of plasma waves-ion fluctuations. The nonthermal tail formed during the stabilization of the precipitated electrons can stabilize the Anomalous Doppler Resonance instability and prevent the isotropization of the energetic electrons. The precipitating electrons modify the way the return current is carried by the background plasma. In particular, the return current is not carried by the bulk of the electrons but by a small number of high velocity electrons. For beam/plasma densities ≳ 10−3, this can reduce the effects of collisions and heating by the return current. For higher density beams where the return current could be unstable to current driven instabilities, the effects of strong turbulence anomalous resistivity is shown to prevent the appearance of such instabilities. Our main conclusion is that the beam-return current system is interconnected and how the return current is carried is determined by the beam generated strong turbulence.