Quantitative Analysis of Wave Absorption near Cyclotron Resonance in an Inhomogeneous Magnetic Field

本文定量地研究了电磁波在回旋共振附近的传播和吸收，分析了磁镜几何中带电粒子的非线性运动。与回旋共振附近的电磁波的相互作用引起粒子的随机运动。我们估计了粒子运动变为随机的波幅阈值，并通过数值计算加以证实。波在非均匀磁场中的传播和吸收的自洽分析需要动力学公式。本文从非均匀磁场中未受扰动的粒子轨道出发，导出了积分微分形式的波动方程。我们用数值方法求解了从回旋共振高场一侧入射的电子回旋波，计算了波场的空间分布、吸收功率和反射系数。当磁场梯度适中时，入射波在回旋共振附近被完全吸收，不发生反射。这与常规冷等离子体分析一致。然而，在陡梯度的情况下，一部分入射波被反射，因为由于有限的温度，波数保持有限。功率沉积曲线的密度和温度依赖性也被检查。

Propagation and absorption of electromagnetic waves near cyclotron resonance is quantitatively investigated.We have analysed nonlinear motion of charged particles in a magnetic mirror geometry. The interaction with an electromagnetic wave near cyclotron resonance gives rise to stochastic motion of the particles. We have estimated a threshold of wave amplitude where the particle's motion becomes stochastic, and confirmed it by numerical computation.The self-consistent analysis of wave propagation and absorption along an inhomogeneous magnetic field requires kinetic formulation. Based on an unperturbed particle orbit in the inhomogeneous magnetic field, we have derived the wave equation in an integrodifferential form. We have solved it numerically to describe the electron cyclotron wave incident from the high field side of the cyclotron resonance.The spatial profiles of the wave field and the absorbed power as well as the reflection coefficient are calculated. When the gradient of the magnetic field is moderate, the incident wave is completely absorbed near the cyclotron resonance and no reflection occurs. This is consistent with a conventional cold plasma analysis. In the case of steep gradient, however, a part of the incident wave is reflected, since the wave number remains finite owing to the finite temperature. The density and temperature dependence of the power deposition profile is also examined.