Interpretation of the Finite Pressure Gradient Effects in the Reversed Shear AlfvĂŠn Eigenmode Theory

N.N. Gorelenkov, G.J. Kramer, R. Nazikian

关键词: APPROXIMATIONS;    DISPERSION RELATIONS;    FREQUENCY MEASUREMENT;    PLASMA;    PLASMA PRESSURE;    PRESSURE GRADIENTS;    REVERSED SHEAR;    SPECTROSCOPY Tokomaks;    MHD;   

DOI  :  10.2172/960228
RP-ID  :  PPPL-4294
PID  :  OSTI ID: 960228
Others  :  TRN: US0904414

学科分类：原子、分子光学和等离子物理

美国|英语

来源: SciTech Connect

【 摘 要 】

Ideal MHD equations employed in the NOVA code are analyzed analytically and numerically in order to investigate the role of the pressure gradient on global reversed shear AlfvĂŠn eigenmodes (RSAEs) or AlfvĂŠn cascades. We confirm both numerically and analytically conclusions obtained earlier using the ideal MHD code NOVA and analytically that the plasma pressure gradient plays a key role in the existence condition and in the dispersion relation for the mode. The effect of the plasma pressure gradient is to shift the mode frequency up at the low part of the RSAE frequency chirp and downshift the mode frequency when the frequency approaches the TAE gap This finding is opposite to predictions in a recent publication , where the pressure gradient is found to be always stabilizing by means of downshifting the RSAE frequency and enhancing its in- teraction with the continuum. We resolve this discrepancy by showing that neglecting the pressure gradient effect on the plasma equilibrium (modification of the Shafranov shift and the averaged curvature) leads to conclusions at variance to the numerical and analytical results presented here. A new variational approximation of the RSAE is introduced which compares remarkably well with NOVA solutions. With this new approximation we clearly demonstrate the diagnostic potential and limitations of the RSAE frequency measurement for MHD spectroscopy.