NONLINEAR TREATMENT FOR SOLAR RADIO SPIKES .2. THE FASTEST GROWING MODE

Linear (temporal and spatial) growth rates of high-frequency normal mo des are calculated when an unstable fast electron population with a tw o-side loss cone and power-law energetic distribution exists in a magn etized plasma. The dominant mode is shown to be: fundamental X-mode if Y = omega(pe)/omega(Be) < 0.2-0.3, lh-mode if 0.2-0.3 < Y < 0.5-0.8, fundamental Z-mode if 0.5-0.8 < Y < 0.9 for a broad energetic spectrum of electrons (10 keV less than or similar to E less than or similar t o 200 keV). These modes are generated by different groups of fast elec trons. The results presented can be used for further study of nonlinea r effects in ECM problems including quasilinear relaxation of the inst ability From the obtained dependence of the growth rates on the bandwi dth of the electron spectrum we predict that the spiky emission should have no correlation with electron gamma-ray Bremsstrahlung, contrary to the correlation with hard X-ray emission. We find that the growth r ates can grow with the decrease of the electron distribution anisotrop y (in a certain range of the anisotropy parameter value). This behavio ur explains naturally a super-exponential (gaussian) rise phase of the spikes discovered in observations.