Alfven Ion Cyclotron Instability Research Articles

Acceleration of Ion Rings by Collapsing Liners

We have established the conditions for the absence of Alfven ion-cyclotron instability in the formation and subsequent acceleration of ion rings by collapsing cylindrical plasma liners.

Ускорение ионных колец сжимающимися лайнерами

The conditions for the absence of Alfven ion-cyclotron instability during the creation and subsequent acceleration of ion rings by compressed cylindrical plasma liners are established

Evolution of anisotropic distributions of weakly charged heavy ions downstream collisionless quasiperpendicular shocks

Hybrid simulations of quasiperpendicular collisionless shocks (QRCS) in multicomponent plasmas have revealed that weakly charged ions can keep anisotropic nonequilibrium distributions at relatively long distances downstream the shock front. However, analytic considerations suggest that such distributions lead to growth of the Alfven ion cyclotron (AIC) instability, which in turn governs isotropisation. Hence, we have conducted targeted hybrid simulations of QRCS with increased accuracy, which appeared to agree with the analytical predictions and suggest that the nonequilibrium distributions eventually relax due to the AIC instability. On another hand, downstream electromagnetic instabilities generated by anisotropic particle distributions may affect the energy balance, therefore influencing macroscopic shock parameters, such as the compression ratio. Simulations of QRCS with parameters close to those of the heliospheric termination shock measured by the Voyager mission, showed that an admixture of just 0.7% (by mass) of oxygen decreases the compression ratio by 3-4%. Thus, one might conclude that along with the effect of the pickup ions, the multi-species composition of the interplanetary plasma can add to the observed decrease of the shock compression.

Energy spectrum of longitudinal ion losses in the GDT facility under development of Alfvén ion-cyclotron instability

The influence of Alfven ion cyclotron instability on the longitudinal losses of particles and energy from the GDT gas-dynamic trap was studied experimentally. To record the energy spectrum of ions escaping from the facility along magnetic field lines, a wide-range energy analyzer was attached to the expander. Processing of the experimental data made it possible to determine the time evolution of the ion energy distribution function and showed that the relative increase in the loss power during the development of instability did not exceed 1%. This result confirms the main conclusion of the theoretical model describing the interaction between an Alfven wave and resonance particles and predicting that this microinstability insignificantly affects the confinement of hot ions in open magnetic traps.

Alfvén ion-cyclotron instability in an axisymmetric trap with oblique injection of fast atoms

Conditions for the onset of Alfven ion-cyclotron instability and the spatial structure of unstable modes in an axisymmetric mirror trap with oblique injection of fast atoms are studied. It is shown that the main contribution to instability comes from the inverse population of ions in the velocity space domain into which atoms are injected. Using the distribution function of fast ions obtained by approximately solving the Fokker-Planck equation, the instability threshold in terms of β⊥ is determined in the Wentzel-Kramers-Brillouin approximation as a function of the geometric parameters and the parameters of injection and target plasma. It is demonstrated that the stability threshold increases substantially when the radius of the hot plasma decreases to a size comparable with the Larmor radius of fast ions. It is shown that the perturbed fields near the axis and at the plasma periphery can rotate in opposite directions, which is important for the interpretation of experimental data.

Study of Microinstabilities in Anisotropic Plasmoid of Thermonuclear Ions

The following work presents the results of investigation of microinstabilities in the anisotropic synthesized hot ion plasmoid (SHIP). Plasmoid is located in a small mirror section that is installed at one side of the GDT facility, which is an axially symmetric magnetic mirror device of gas dynamic trap type. To define the type and the parameters of the developing microinstability a set of high-frequency electrostatic and magnetic probes was used. The microinstability observed in the additional section of GDT is the Alfven ion cyclotron instability (AIC), because of small azimuthal wave numbers, magnetic field vector rotating in the direction of ion gyration and oscillation frequency below the actual ion cyclotron frequency. AIC instability threshold was registered at the following plasma parameters: fast ion density n > 3 × 1013 cm-3, ratio of ion pressure to magnetic field pressure β ≈ 0.02, anisotropy A = 40, ai/Rp ≈ 0.23, where ai is the ion gyroradius and Rp is the plasmoid radius.

Suppression of longitudinal losses in a gas-dynamic trap by using an ambipolar mirror

The efficiency of utilizing ambipolar mirrors for suppression of longitudinal losses of particles and energy in a gas-dynamic trap (GDT) was investigated. An additional relatively small axisymmetric mirror cell was installed in one of the facility ends. Hydrogen or deuterium atomic beams with an energy of 22 keV and equivalent current density of up to 1 A/cm2 were injected into the additional cell at an angle of 90° to the facility axis. Trapping of the beams with a total power of 800 kW by the plasma in the additional cell leads to the formation of a hot ion population with an anisotropic velocity distribution, a mean energy of 13 keV, and a density of up to 4.5 × 1013 cm−3. It is shown that the confinement of hot ions in the additional cell is determined by classical processes, such as charge exchange on the beam atoms and collisional deceleration by electrons, in spite of the onset of Alfven ion-cyclotron instability at fast ion densities higher than 2.5 × 1013 cm−3. The effect of ambipolar confinement manifests itself in that, at hot ion densities higher than 3 × 1013 cm−3, the flux density of ions escaping from the trap in the mode with beam injection decreases fivefold as compared to that without injection. In this case, the density of the Maxwellian plasma component in the central cell is about 2.5 × 1013 cm−3. The efficiency of suppression of longitudinal particle losses by the ambipolar mirror substantially exceeds estimates obtained for both collisional (gas-dynamic) and collisionless (adiabatic) confinement modes. Qualitatively, this is because, in the GDT experiments, the mode of warm plasma confinement is transitional between the gas-dynamic and adiabatic modes and the use of an ambipolar mirror facilitates a transition from the lossy gas-dynamic mode into a nearly adiabatic one.

Control of the energetic proton flux in the inner radiation belt by artificial means

Earth's inner radiation belt located inside L = 2 is dominated by a relatively stable flux of trapped protons with energy from a few to over 100 MeV. Radiation effects in spacecraft electronics caused by the inner radiation belt protons are the major cause of performance anomalies and lifetime of Low Earth Orbit satellites. For electronic components with large feature size, of the order of a micron, anomalies occur mainly when crossing the South Atlantic Anomaly. However, current and future commercial electronic systems are incorporating components with submicron size features. Such systems cannot function in the presence of the trapped 30–100 MeV protons, as hardening against such high‐energy protons is essentially impractical. The paper discusses the basic physics of the interaction of high‐energy protons with low‐frequency Shear Alfven Wave (SAW) under conditions prevailing in the radiation belts. Such waves are observed mainly in the outer belt, and it is believed that they are excited by an Alfven Ion Cyclotron instability driven by anisotropic equatorially trapped energetic protons. The paper derives the bounce and drift‐averaged diffusion coefficients and uses them to determine the proton lifetime as a function of the spectrum and amplitude of the volume‐averaged SAW resonant with the trapped energetic protons. The theory is applied to the outer and inner radiation belts. It is found that the resonant interaction of observed SAW with nT amplitude in the outer belt results in low flux of trapped protons by restricting their lifetime to periods shorter than days. A similar analysis for the inner radiation belt indicates that broadband SAW in the 1–10 Hz frequency range and average amplitude of 25 pT would reduce the trapped energetic proton flux by more than an order of magnitude within 2 to 3 years. In the absence of naturally occurring SAW waves, such reduction can be achieved by injecting such waves from ground‐based transmitters. The analysis indicates that such reduction requires injection of less than 10 kW of SAW power. Increasing the power will result in the further decrease of the trapped flux. The paper concludes with a brief discussion of techniques that can inject such waves using ground‐based transmitters.

Study of Microinstabilities in Anisotropic Plasmoid of Thermonuclear Ions

The following article presents the results of investigation of microinstabilities in the anisotropic synthesized hot ion plasmoid (SHIP). Plasmoid is located in a small mirror section that is installed at one side of the GDT facility in Budker Institute of Nuclear Physics, Novosibirsk, which is an axially symmetric magnetic mirror device of gas dynamic trap type. The magnetic field on axis is in the range of 2.5 Tesla and the mirror ratio is ~ 2. The additional mirror section is filled with background plasma streaming from the central cell of GDT. To create the population of hot ions with strong anisotropy two focused neutral beams with energy of 21–23 keV are injected perpendicularly to the direction of magnetic field. Ionisation of the beams generates the high-energetic ion component with the density of about 5x1013 сm–3 and mean energy about 13 keV. The distribution function of fast ions is thus strongly anisotropic in the phase space with the ratio E⊥ / E& ~ 50. To define the type and the parameters of the developing microinstability a set of high-frequency electrostatic and magnetic probes was used. The microinstability observed in the additional section of GDT is the Alfven ion cyclotron instability (AIC), because of small azimuthal wave numbers, magnetic field vector rotating in the direction of ion gyration and oscillation frequency below the actual ion cyclotron frequency. AIC instability threshold was registered at the following plasma parameters: fast ion density n > 3 · 1013 см–3, ratio of ion pressure to magnetic field pressure β ≈ 0.02, anisotropy A ≈ 35, ai / Rp ≈ 0.23, where ai is the ion gyroradius and Rp is the plasmoid radius.

開放端磁場プラズマの物理 2.ミラープラズマの安定性

The stability of mirror-confined plasmas is reviewed. The equilibrium of mirror-confined plasmas is first briefly discussed. Then, MHD stability is studied based on an energy priciple with the paraxial approximation and flute and ballooning interchange-mode equations are derived. The effects of E×B rotation due to an ambipolar electric field and the finite Larmor radius of ions on MHD stability are briefly described. Alfven ion cyclotron instability driven by the temperature anisotropy of ions, and E×B drift shear stabilization of electrostatic drift waves due to an ambipolar electric field are reported.

Thermal anisotropies in the solar wind: Evidence of heating by interstellar pickup ions?

A recent paper by Gray et al. [1996] shows that the Alfvén ion cyclotron instability is generated by newly created pickup ions and heats the thermal solar wind protons in the direction perpendicular to the magnetic field. This instability operates most effectively in regions where the plasma β is low, so this mechanism predicts that the ratio of the temperatures perpendicular and parallel to the magnetic field should be larger in low‐β regions of the solar wind. We look for this effect in ISEE‐3 and Voyager 2 data. The near‐Earth ISEE‐3 data show no evidence for greater thermal anisotropies at low β. Voyager 2 data obtained between 1 and 8 AU show that the ambient proton thermal anisotropy is a function of β, with parallel temperatures generally greater than perpendicular temperatures except when β is small. For Voyager 2 data, the average ratio of perpendicular to parallel temperature is about 0.9, but this ratio is ∼2 when β is less than 0.1 and ∼4 when β is less than 0.01.

Heating of the solar wind by pickup ion driven Alfvén ion cyclotron instability

Pickup ions in a ring velocity distribution are unstable to several kinetic plasma instabilities. At large heliocentric distances where the overall plasma β (ratio of kinetic to magnetic energy) is dominated by the energy density of interstellar pickup ions and pickup is perpendicular to the interplanetary magnetic field, the dominant of these is the Alfvén ion cyclotron instability (AIC). We demonstrate by hybrid particle simulation that, for conditions where the solar wind β is low, AIC driven by the pickup ions couples to the solar wind. The result is perpendicular heating, leading to an anisotropic solar wind distribution. This process may contribute to enhanced solar wind temperatures at large heliocentric distances and may allow for indirect measurement of interstellar pickup ions.

Suppression of Alfvén Ion Cyclotron Instability in a Mirror by End Plugging

The effect of end plugging of the ion on the Alfven ion cyclotron instability in a mirror-confined plasma is studied. The dispersion equation in the uniform-plasma approximation is derived by assuming a loss cone distribution of the ion, taking into account the end plugging, and is solved numerically. It is shown that the end plugging effect of filling the loss cone mainly causes the reduction of the temperature anisotropy of the ion, leading to the suppression of the instability.

The Alfvén ion-cyclotron instability. Simulation theory and techniques

The numerical properties of a particle-ion, fluid-electron computer simulation code, used in the study of the parallel-propagating electromagnetic Alfven ion-cyclotron (AIC) instability, are examined. A numerical odd-even mode is suppressed by means of a two-timestep averaging method. Excellent energy conservation is obtained by using a method similar to the Boris particle mover to advance the transverse fields. Linear growth rates obtained' from the code differ substantially from those predicted by uniform Vlasov theory, here derived using a muitifluid model. Short wavelengths in particular show substantial growth rates when damping is predicted, and additionally show strong linear mode coupling. Positive growth rates are even observed in the case of a Maxwellian ion distribution. Disagreement is also generally found among short-wavelength mode frequencies. These inconsistencies are resolved by taking into consideration general grid and discrete-particle effects of the simulation model. A theoretical study reveals a real, physical process by which an ion distribution may collisionlessly relax via short-wavelength AIC instabilities acting resonantly on small portions of the distribution function. This process is combined with a linear mode coupling theory and other characteristics of the AIC instability to explain all observed differences. Nonlinear short-wavelength saturation levels are also obtained and their relevance to other field-aligned, electromagnetic simulations is discussed.

Magnetic field and density fluctuations at perpendicular supercritical collisionless shocks

Perpendicular collisionless shocks are studied by means of two‐dimensional hybrid (particle ion, fluid electron) simulations, with emphasis on the relaxation of the highly anisotropic ion distribution that arises primarily from reflection of some of the incident ions but also adiabatic compression of the other, directly transmitted ions and the related growth of low frequency electromagnetic waves. It is commonly assumed that the waves are due to the Alfven ion cyclotron instability that propagate parallel to the ambient magnetic field (k⊥ = 0) and that the isotropization of the ions due to pitch angle scattering by the waves and the corresponding modification of the wave spectrum is quasi‐linear. It is shown that this is indeed a reasonably good description downstream of the shock front, behind the magnetic overshoot. However, at the shock ramp there is a large discrepancy between the wavelengths measured in the simulations and those predicted by linear theory, and large density and magnetic field oscillations parallel to the ambient magnetic field are also seen. By comparing results for both high and low ion beta cases, it is shown that these effects can be understood in terms of obliquely propagating (k⊥ ≠ 0) modes, more likely due to the Alfven ion cyclotron instability instead of the (drift) mirror instability, although a more complete explanation awaits the derivation and analysis of an appropriate dispersion relation describing the growth and coupling of low‐frequency modes in the inhomogeneous high beta environment of the shock. The observational consequences of these results and their application to improving nonlocal leakage models for the ion foreshock are also discussed.

Angular dependence of high Mach number plasma interactions

In this paper a 2‐1/2‐dimensional hybrid code is used to examine the collisionless large spatial scale (kc/ωpi ∼ 1) low‐frequency (ω ∼ ωci) interaction initiated by a plasma shell of finite width traveling at high Alfven Mach number relative to a uniform background plasma. Particular attention is given to the angle of the relative velocity relative to the ambient magnetic field for the range of angles 0 < θ < π/2. An attempt is made to parametrize some of the important physics including the Alfven ion cyclotron instability, the field‐aligned electromagnetic ion counter streaming instability, mixing of the plasma shell with the background ions, and structuring of the interaction region. These results are applicable to various astrophysical interactions such as bow shocks and interplanetary shocks.

Alfvén Ion-Cyclotron Instability: Its Physical Mechanism and Observation in Computer Simulation

The physical mechanism of the Alfven ion-cyclotron instability due to ion-temperature anisotropy in a high-..beta.. plasma is explored. We have observed evidence for the proposed mechanism in runs on a magnetostatic particle simulation code. Saturation and stabilization of the instability are discussed on the basis of the present mechanism.