Maxwellian Component Research Articles

Nonlinear Stabilization of Single, Resonant, Loss-Cone Flute Instabilities

The evolution of linearly unstable, high-frequency (ω≈nΩ), flutelike (k‖ = 0), electrostatic modes which can occur in a multicomponent, magnetic-mirror-confined collisionless plasma has been studied by computer simulation using a one-and-one-half dimensional model. Approximately one-quarter of the particles in the initial velocity distributions formed a warm, Maxwellian background component; the remainder belonged to a hot, linearly stable, loss-cone component. The early evolution of single wave (either traveling or standing), resonant instabilities agrees well with linear theory. A rapid, coherent heating of the warm component occurs and spatial harmonics of the unstable wave appear. The electrostatic field of the wave then saturates at an energy level as much as two orders of magnitude lower than those reported in previous simulation studies of the same and related instabilities or predicted from earlier nonlinear analysis. The saturation levels and early post-saturation behavior are in agreement with a recently reported nonlinear analysis which was motivated by the results reported here.

熱中性子化の特性スペクトル

The behavior of the neutron energy spectrum in a bare homogeneous moderator after the introduction of a burst of neutrons has been studied theoretically. The problem is reduced to an eigenvalue problem for a self-adjoint integral operator governing the neutron thermalization.In an infinite system, it has been shown that the Maxwellian component of the spectrum does not couple with higher modes which are orthogonal to the former and contribute nothing to the actual neutron density when integrated. The asymptotic neutron spectrum and the diffusion cooling are formulated most conveniently in the present scheme.The formalism is a general one and may be applied to any scattering model with due labor of computations. Numerical calculations has been done for heavy gaseous moderators.