Presence Of Ion-acoustic Turbulence Research Articles

Моделирование коронального источника жесткого рентгеновского излучения в турбулентной плазме солнечных вспышек

The kinetics of electron beams accelerated in the collisional plasma of solar (stellar) flares is considered, taking into account the stationary ion-acoustic mode localized at the magnetic looptop and magnetic fluctuations. The astrophysical aspect of the propagation process is related to the interpretation of hard X-rays in the plasma of flare loops. It is shown that when the plasma density in the coronal part of the solar flare loops does not exceed 1010 cm-3, taking into account the additional scattering on the ion-acoustic mode with the ratio of the turbulence energy density to the thermal energy of the plasma ~5 * 10-5-10-3 and magnetic fluctuations with a level of 5·10-2 does not lead to the appearance of a bright hard X-ray source in the coronal part of the loop in the model with the isotropic pitch-angle distribution of accelerated electrons. In the anisotropic case with a hard electron energy spectrum, the coronal hard X-ray source, in the presence of ion-acoustic turbulence, can exist for a short time after the beginning of turbulence generation. And only in the case of a soft energy spectrum of accelerated electrons (power spectrum index >5) and a relatively high plasma density at the magnetic looptop >1010 cm-3, a bright coronal hard X-ray source is generated at energies of 25-50 keV, regardless of the pitch-angular distribution of accelerated electrons at the moment of injection. A significant effect of turbulence on the distribution of the linear degree of hard X-ray polarization along the loop is shown, leading to a decrease in the extreme values in the coronal part by 5-35%. The integral values of the hard X-ray polarization do not exceed 10%.

Relativistic plasma maser interaction in the presence of ion acoustic turbulence

The plasma maser interaction between the high frequency nonresonant ordinary mode and low frequency resonant ion acoustic mode in a relativistic plasma has been studied for the first time. It has been shown that the growth rate of the high frequency wave occurs through the plasma maser interaction between relativistic electrons and the ion acoustic wave turbulence.

Plasma turbulent bremsstrahlung.

Plasma turbulent bremsstrahlung is a radiation of high frequency plasma mode produced by the scattered electrons due to the effective turbulent collisions associated with low frequency fluctuations. It is found that the spontaneous emission term in the quasilinear effect is responsible for the mechanism. The Langmuir mode becomes unstable when electrons resonate with low frequency modes in the presence of ion acoustic turbulence resulting in frequency upconversion.

Plasma conditions for non-Maxwellian electron distributions in high current discharges and laser-produced plasmas

Results from the standard quasilinear theory of ion-acoustic and Langmuir plasma microturbulence are incorporated into the kinetic theory of the electron distribution function. The theory is then applied to high current discharges and laser-produced plasmas, where either the current flow or the nonlinear laser-light absorption acts, respectively, as the energy source for the microturbulence. More specifically, the theory is applied to a selenium plasma, whose charge state is determined under conditions of collisional-radiative equilibrium, and plasma conditions are found under which microturbulence strongly influences the electron kinetics. In selenium, we show that this influence extends over a wide range of plasma conditions. For ion-acoustic turbulence, a criterion is derived, analogous to one previously obtained for laser heated plasmas, that predicts when Ohmic heating dominates over electron-electron collisions. This dominance leads to the generation of electron distributions with reduced high-energy tails relative to a Maxwellian distribution of the same temperature. Ion-acoustic turbulence lowers the current requirements needed to generate these distributions. When the laser heating criterion is rederived with ion-acoustic turbulence included in the theory, a similar reduction in the laser intensity needed to produce non-Maxwellian distributions is found. Thus we show that ion-acoustic turbulence uniformly (i.e., by the same numerical factor) reduces the electrical and heat conductivities, as well as the current (squared) and laser intensity levels needed to drive the plasma into non-Maxwellian states.These effects are large over a wide range of plasma temperatures and densities such as found in Z-pinch, laser-produced, or opening switch plasmas. The reduction in laser intensity thresholds for generating non-Maxwellian states is a result of microturbulence enhanced laser absorption, which can be observed at any laser intensity. Thus, if microturbulence is the cause of the heat flux inhibition, then the magnitude of the inhibition might be directly observed through the use of probe-laser beams. Finally, we calculate the laser intensities and the current densities needed to change the electron distributions in the presence of ion-acoustic turbulence. These calculations are carried out by assuming that the electrostatic fluctuations scale as the square root of the electron plasma parameter in a weakly microturbulent selenium plasma. The laser intensities calculated in this example are found to be only slightly in excess of those used in recently conducted experiments.

Generation of axial magnetic fields in a laser-produced plasma by a turbulent dynamo

It is shown that axial magnetic fields earlier observed in laser-produced plasma experiments can be generated by the action of a turbulent dynamo in the presence of ion-acoustic turbulence in an underdense plasma.

Instability of the heat flux in a laser-produced plasma in the presence of an ion acoustic instability

We investigate a heat flow instability arising due to transverse perturbation of an initially uniform flow. Its growth rate is shown to be determined by the magnitude of the heat flux. The presence of ion acoustic turbulence driven by the flux itself leads to stabilization of the instability due to a decrease of the transverse heat flow.

Instability of the critical surface of a laser-produced plasma in the presence of ion-acoustic turbulence

The critical surface can be unstable to coherent rippling perturbations due to the action of negative pressure induced by the random magnetic field associated with ion-acoustic turbulence. The negative magnetic pressure occurs if there exists a preferential orientation of the random magnetic field (anisotropy of the ion-acoustic turbulence) when the nonpotential component of the magnetic pressure more than compensates the potential part.

Resistivity Phenomena in Multi-Ion Plasma with Ion Acoustic Turbulence

The effect of different species of ions on the resistivity of a plasma in the presence of ion acoustic turbulence has been studied. Results have been applied to the case of hydrogen-helium plasma mixture. The variation of drift velocity with Te/Ti for quasi stationary fluctuation levels for different percentages of light and heavy ions available in the plasma is also investigated. It is found that the variation is quite significant even for small percentages of light ion contamination.

Ion-acoustic resistivity of a multicomponent plasma

The expression for a general dispersion relation in the presence of ion-acoustic turbulence has been derived for a two-ion plasma and is used to study its effect on the turbulent resistivity. Results have been applied to the case of a hydrogen-helium plasma mixture. The effect of the addition of light ions on the variation of the drift velocity and resistivity of the plasma with T e T i is investigated for quasi-stationary fluctuation levels.

Determination of the electric field in plasmas with turbulence

The electric field in the presence of ion-acoustic turbulence is measured by an emissive floating probe. The measured value is compared with that by a cold Langmuir probe.

Propagation of Test Waves in the Presence of Ion Acoustic Turbulence in Plasmas

Ion acoustic turbulence is excited by the current-driven ion acoustic instability in a dc discharge plasma. By measuring the dispersion relation of test waves in the plasma with the ion acoustic turbulence, we find that the wave energy transfers from high frequencies to low frequencies and the phase velocity of the ion acoustic wave becomes smaller than the ion acoustic velocity in low frequencies near the peak of the turbulence spectrum. These experimental results can be interpreted theoretically.