The energy injection into waves with a zero group velocity

The frequency maxima of electron cyclotron harmonic (ECH) waves provide str ong responses to sounding in various plasma regimes in the solar system. Th e frequency maxima correspond to waves for which the group velocity and thu s the energy propagation velocity in the plasma frame of reference is zero. A particle-in-cell (PIC) code is employed to show that the propagation of wave energy at a non-zero velocity, necessary to couple energy from a stati onary antenna to the plasma, is accomplished by propagating wave precursors . The undamped waves at the frequency maxima of the ECH branches are nonpro pagating hence the waves remain localized. It is demonstrated that the nonp ropagating waves, built up by the wave precursors, are standing waves. The standing wave generation is followed from the linear to nonlinear regimes. For nonlinear emission amplitudes the emission causes a plasma density depl etion close to the antenna. The depletion is shown to trigger a modulationa l instability in which the ECH wave collapses. The generated nonlinear stan ding wave also develops an electromagnetic component which couples the elec trostatic ECH waves to the fast extraordinary wave. (C) 1999 American Insti tute of Physics. [S1070-664X(99)00707-7].