Doppler splitting of electron cyclotron absorption resonance in plasmas

Abstract

The Gaussian broadening of absorption lines due to the Doppler effect is well known. However, it is shown here for the first time that Doppler splitting occurs for the ordinary-mode electron-cyclotron-resonance absorption in plasmas. Although this absorption is due to the finite size of the electron Larmor orbits it is mainly determined by $T_{?}$ and is only weakly dependent on $T_{\perp }$ via cyclotron-overstability-type terms. This is in contrast to intuitive expectations which would suggest that finite-Larmor-radius effects should depend strongly on $T_{\perp }$.