Propagation and damping of linearly converted electron cyclotron quasi-longitudinal waves

The propagation and spatial damping of linearly converted electron cyclotron (EC) quasi-longitudinal waves in a magnetized plasma are investigated both analytically and numerically. The dispersion properties of these waves are analysed in the frequency range around the fundamental EC frequency and its second harmonic. Results of the numerical analysis, showing the solution trajectory of the least damped quasi-longitudinal mode in a weakly inhomogeneous plasma, are presented. Large values of the normalized optical depth characterize the damping of the slow backward mode at either the first or the second EC harmonic. The collisional wave damping in low temperature plasmas is also discussed. The results obtained indicate that the strong damping of linearly converted EC quasi-longitudinal waves provides an efficient mechanism for the microwave preionization and plasma heating. (orig.)