Study of Relativistic Electromagnetic Ion Cyclotron Instabilities Driven by MeV Ions

• Main Authors: Jung-Da Huang, 黃榮達
• Other Authors: K. R. Chen
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/dcqh7q

碩士 === 國立成功大學 === 物理學系碩博士班 === 90 === 　　The relativistic instability of electromagnetic ion cyclotron waves propagating across the magnetic field driven by fast ions of MeV energy is investigated. Both kinetic theory and MHD theory are employed to derive the dispersion relation. The conditions, growth rates, and wave frequencies are studied by analytical and numerical calculation of the dispersion relation. 　　The relativistic instability is reactive, as in contrast to the inversed Landau instability. In addition to a cubic instability, there is a special quadratic instability. While the maximum growth rate of all know instabilities is determined by their drives (e.g., the fast ion density), the threshold of the quadratic instability is determined by the fast ion density; but, its maximum growth is independent of the fast ion density and is determined by the slow ion density instead. 　　Due to the wave magnetic field is much larger than the electric field, the dielectric constant of the cold plasma part is large. The instabilities are two-gyro-stream type and are raised due to the coupling of the first order pole of slow ions and the second order pole of fast ions. The wave frequency of the cubic instability is close to the harmonic fast ion cyclotron frequency and the maximum growth is with a 1/3 power of fast ion density. However, when the slow ion density is low, the wave frequency is very close to the slow ion harmonic cyclotron frequency and, thus, the cubic term in the dispersion relation can be neglected and the dispersion relation becomes quadratic so as the instability. 　　The relativistic quadratic instability has some special characteristics. It occurs when the ions’ frequency mismatch can be canceled by the coefficient of the relativistic second order pole of fast ions; that is, there is a threshold of fast ion density for the instability. But, the maximum growth rate depends on the slow ion density (not fast ion density). The higher is the slow ion density; the higher is the maximum growth rate, the lower is the fast ion density threshold, and the smaller is the mismatch of the wave and fast ion harmonic cyclotron frequencies.