The Cavity Q for Ergodic Eigenmodes
The Cavity Q for Ergodic Eigenmodes
复制标题
遍历本征模态的腔 Q
DOI：
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发表时间：
1981
期刊：
影响因子：
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通讯作者：
W. Manheimer
中科院分区：
文献类型：
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作者：
E. Ott;W. Manheimer
摘要：我们在这里考虑的问题，计算一个非常过模，（波长<<腔尺寸）不规则形状的谐振腔由于在墙壁上的电磁辐射的吸收的Q。我们进一步假设腔体内的体积可以是真空的，或者部分填充有各向异性非均匀电介质或等离子体。电介质的标度长度和壁的曲率半径都被假定为远大于辐射波长。然而，在腔壁附近，假设真空。我们的主要兴趣是在磁约束等离子体的应用。例如，考虑一个含有热等离子体的托卡马克，它以回旋频率及其谐波辐射。一个重要的问题是，有多少回旋辐射被壁吸收，又有多少被等离子体重新吸收。一般来说，这可以用射线跟踪代码来计算，其中跟踪许多射线，并计算沿着每条射线路径的吸收和发射。然而，如果等离子体是光学薄的，就像它在高次谐波处一样，如果壁处的反射系数接近1，那么在人们可以看到有多少能量沉积在壁中之前，射线必须被跟踪很长的距离。本文利用遍历定理计算了波多次反弹而未被吸收时的壁面吸收。
Abstract : We consider here the problem of calculating the Q of a very overmoded, (wavelength << cavity size) irregularly shaped resonant cavity due to absorption of the electromagnetic radiation at the walls. We assume further that the volume inside the cavity can be either vacuum, or else partially filled with anisotropic inhomogeneous dielectric or plasma. Both the scale length of the dielectric and the radius of curvature of the walls are assumed much larger than the radiation wavelength. However, near the cavity walls, a vacuum is assumed. Our main interest here is in applications concerning magnetically confined plasmas. For instance consider a tokamak containing a hot plasma which radiates at the cyclotron frequency and its harmonics. An important issue is how much of this cyclotron radiation is absorbed by the walls and how much is reabsorbed by the plasma. Generally this can be calculated with a ray tracing code where many rays are followed and the absorbtion and emission are calculated along each ray path. However if the plasma is optically thin, as it would be at the higher harmonics, and if the reflection coefficient at the wall is near unity the rays would have to be followed for long distances before one could see how much energy is deposited in the wall. In this paper we utilize the ergodic theorem to calculate the wall absorbtion for the case where the wave makes many bounces and before it is absorbed.