Showing papers by "Marshall N. Rosenbluth published in 1962"

Anomalous Diffusion Arising from Microinstabilities in a Plasma

Abstract: A plasma is considered in which a Maxwellian distribution of electrons with thermal velocity ve and drift velocity vD is drifting relative to a Maxwellian distribution of ions with thermal velocity vi. For vD ≲ ve the usual ion acoustic waves are stable, however, electrostatic ion cyclotron waves with ω ≅ Ωi are unstable for vD ≳ 5vi. In the case when 5vi ≲ vD ≲ ve, and Te/Ti < 2 the electrostatic ion cyclotron waves grow to a nonlinear equilibrium spectrum. This spectrum of waves leads to a diffusion of electrons across the field lines with a diffusion coefficient D = αρ2eΩe, where ρe is the electron Larmor radius and Ωe is the electron Larmor frequency. α, the ratio of the resulting diffusion coefficient to the Bohm diffusion coefficient, is given by a constant × (vD/ve)5(Te/Ti)2.

Trapping Instabilities in a Slightly Inhomogeneous Plasma

Abstract: The stability of an infinite collisionless plasma with a small density gradient in the x direction (using the collisionless Boltzmann equation and Maxwell's equations) confined by a static magnetic field in the z direction, is studied. Unstable modes are found at frequencies near multiples of the ion‐cyclotron frequency Ωi. These modes are electrostatic oscillations transverse to the magnetic field, and have very short wavelengths λ ∼ vd/Ωi, where vd is the (small) drift occasioned by the magnetic‐field inhomogeneity. The phase velocity of the wave is comparable to vd, and resonant interaction leads to the growth. Typical growth rates are large, α ∼ (me/mi) Ωi, but the effect of the instability is minimized by the extremely short wavelength.