On properties of compressional Alfvén eigenmode instability driven by superAlfvénic ions

Properties of the instability of compressional Alfvén eigenmodes (CAEs) in tokamak plasmas are studied in the cold plasma approximation with an emphasis on the instability driven by the energetic minority ion cyclotron resonance heating (ICRH) ions. The goal of the paper is to address a long standing problem of CAE half proton cyclotron harmonic excitation observed in pure deuterium plasma basing on new observations from Joint European Torus. As an example we apply earlier developed theory (Gorelenkov N.N. and Cheng C.Z. 1995 Nucl. Fusion35 1743) to compare two cases: ion cyclotron emission (ICE) driven by charged fusion products and ICRH minority-driven ICE (MICE) (Cottrell G.A. 2000 Phys. Rev. Lett.84 2397) recently observed on JET. Particularly in MICE spectrum, only instabilities with even harmonics of deuterium cyclotron frequency at the low-field-side plasma edge were reported. Odd deuterium-cyclotron frequency harmonics of ICE spectrum with frequencies between the integer cyclotron harmonics of protons can be driven only via the Doppler shifted cyclotron wave–particle resonance of CAEs with fusion products, but are shown to be damped due to the electron Landau damping in experiments on MICE. Excitation of odd harmonics of MICE with high-field-side heating is predicted. Dependence of the MICE instability on the electron temperature is studied and is shown to be strong. Low electron β is required to excite odd harmonics of MICE.