Electrostatic electron cyclotron instabilities near the upper hybrid layer due to electron ring distributions

Eliasson, B. and Speirs, D. C. and Daldorff, L. K. S. (2016) Electrostatic electron cyclotron instabilities near the upper hybrid layer due to electron ring distributions. Plasma Physics and Controlled Fusion, 58 (9). ISSN 0741-3335

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    Abstract

    A theoretical study is presented of the electrostatic electron cyclotron instability involving Bernstein modes in a magnetized plasma. The presence of a tenuous thermal ring distribution in a Maxwellian plasma decreases the frequency of the upper hybrid branch of the electron Bernstein mode until it merges with the nearest lower branch with a resulting instability. The instability occurs when the upper hybrid frequency is somewhat above the third, fourth, and higher electron cyclotron harmonics, and gives rise to a narrow spectrum of waves around the electron cyclotron harmonic nearest to the upper hybrid frequency. For a tenuous cold ring distribution together with a Maxwellian distribution an instability can take place also near the second electron cyclotron harmonic. Noise-free Vlasov simulations are used to assess the theoretical linear growth-rates and frequency spectra, and to study the nonlinear evolution of the instability. The relevance of the results to laboratory and ionospheric heating experiments is discussed.