R. Sugaya

Nonlinear Landau damping of electrostatic waves in an electron beam‐plasma system

The nonlinear Landau damping and growth of electrostatic waves in an electron beam‐plasma system in a magnetic field has been observed experimentally. The space charge wave of the beam decays into the Trivelpiece mode, which is amplified exponentially by increasing the amplitude of the pump wave.

Induced Scattering Due to Nonlinear Landau and Cyclotron Damping of Electromagnetic and Electrostatic Waves in a Magnetized Plasma

General expressions of the matrix elements for nonlinear wave-particle scattering (nonlinear Landau and cyclotron damping) of electromagnetic and electrostatic waves in a homogeneous magnetized plasma are derived from the Vlasov-Maxwell equations. The kinetic wave equations obtained for electromagnetic waves are expressed by four-order tensors in the rotating and cartesian coordinates. No restrictions are imposed on the propagation angle to a uniform magnetic field, the Larmor radius, the frequencies, or the wave numbers. By electrostatic approximation of the dielectric tensor and the matrix elements the kinetic wave equations can be applied to the case in which two scattering waves are electrostatic or they are partially electrostatic. Further, the matrix elements in the limit of parallel or perpendicular propagation to the magnetic field are given.

Ion heating by nonlinear Landau damping of ion Bernstein waves

It is shown theoretically that efficient ion heating occurs by nonlinear Landau damping because of the self‐interaction of ion Bernstein waves, where heating efficiency, nonlinear damping of ion Bernstein waves, nonlinear wave–particle coupling coefficients, and virtual waves have sharp maxima at ω≂(m/2)ωci (m=3,5,7). Ion heating depends on k∥νti/ ωci and becomes significantly large for k∥νti/ ωci ≲0.1.

Nonlinear Landau Electron Heating by Electrostatic Waves in an Electron Beam-Plasma System

Electron heating due to nonlinear Landau damping of electrostatic waves in an electron beam-plasma system is studied theoretically. The fast and slow space charge waves of an electron beam and the Trivelpiece-Gould modes interact nonlinearly with plasma or beam electrons and cause an effective electron heating and a beam relaxation which leads to a saturation of electron heating. For nonlinear interaction with plasma electrons, the virtual (beat) wave produced by the two electrostatic waves can heat plasma electrons by its electron cyclotron damping. On the other hand, for nonlinear interaction with beam electrons, the Trivelpiece-Gould mode enhanced by nonlinear Landau damping can heat plasma electrons by its electron Landau damping. For both cases, the conservation of total energy flux and the existence of the energy transport are proved quantitatively.

Growing and Damping of Space Charge Waves of an Electron Beam due to Nonlinear Landau Damping

We have observed experimentally damping and growing of fast and slow space charge waves of an electron beam due to nonlinear Landau damping in an electron beam-plasma system by using spectrum analysis. The former with positive energy damps and the latter with negative energy grows by nonlinear interaction with the Trivelpiece-Gould mode and the electron beam. The lowest and higher modes of the Trivelpiece-Gould modes with respect to a radial wavelength grow by this nonlinear wave-particle interaction satisfying the resonant condition.

Ion heating due to explosive instability in an ion beam--plasma system

Ion heating by the explosive instability in an ion beam–plasma system is studied theoretically. Two electrostatic waves with negative and positive energies become simultaneously unstable by nonlinear wave–particle interaction (nonlinear Landau damping) with plasma ions accompanying ion heating. The relaxation of the ion beam makes the explosion time of the waves much larger and causes saturation of the ion heating. It is shown quantitatively that the decrement of beam energy is transferred into thermal energies of plasma and beam ions by this explosive instability.

Observation of Nonlinear Landau Damping of Electrostatic Waves in an Electron Beam-Plasma System

The nonlinear Landau damping and growth of electrostatic waves in an electron beam-plasma system in a magnetic field have been observed experimentally. The space charge wave of the beam decays nonlinearly into the Trivelpiece-Gould mode, satisfying the resonant condition ω 0 -ω 1 -( k //0 - k //1 )ν b = m ω c ( m is an integer). This decayed wave can be amplified exponentially by increasing the amplitude of the pump wave. Similarly, an externally launched small amplitude test wave, having the same frequency as the decayed wave, can be amplified at the comparable rate. The nonlinear Landau damping coupling coefficients measured experimentally are in good agreement with theory. The virtual wave has also been observed. The pump wave amplitude decays strongly by the presence of the large amplitude test wave.

Behaviors of electrostatic ion cyclotron waves excited in ion beam-plasma systems☆

Abstract Experimental results are presented for a behavior of the electrostatic ion cyclotron waves excited in an ion beam-plasma system. This wave appears as forward and backward waves with respect to the propagating component along the magnetic field.

Numerical Study of Ion Heating Due to Nonlinear Landau Damping in an Ion Beam-Plasma System

Ion heating due to nonlinear Landau damping in an ion beam-plamsa system is studied numerically by solving a set of equations representing the distortion of ion velocity distribution by this instability, where fast or slow space charge wave of an ion beam decays into Trivelpiece-Gould mode by nonlinear interaction with plasma ions and causes ion heating. A nonlinear Landau damping of a usual type by fast space charge wave shows that the ion temperature grows almost exponentially in initial time and saturates. A nonlinear Landau damping of an explosive type by slow space charge wave with negative energy exhibit an explosion of ion temperature and amplitude of all related waves at an explosion time. Considering effect of ion heating which makes nonlinear wave-particle coupling coefficients reduced, it is found that the explosion time of ion heating by slow space charge wave becomes several times larger than the original explosion time.

Velocity Space Diffusion Due to Induced Scattering of Plasma Waves

The velocity space diffusion equation which describes a distortion of the velocity distribution function due to nonlinear Landau damping of electrostatic waves in a plasma without magnetic field is derived from the Vlasov-Maxwell equations by perturbation theory. The conservation laws for total energy and momentum densities of waves and particles are verified, and the time evolutions for energy and momentum densities of particles are given by means of nonlinear wave-particle coupling coefficient in kinetic wave equation. The obtained equations can be also available for analysis of energy transfer between waves and particles caused by nonlinear Landau damping due to non-magnetized particles in a magnetized plasma.