Generalized theory of helicon waves. II. Excitation and absorption

density shells. 5,6 In doing this, they used the exact constant- density solution in each shell and required that the fields be continuous at the interfaces, thus neglecting the charges and currents there. In this work, we derive analytic expressions for the density-gradient terms and find that these terms are essential to the mode-coupling mechanism ~our results repro- duce those of previous authors 7 when TG waves may be neglected!. These effects could have been included in the shell model if the proper boundary conditions had been used. In Sec. IV, we give numerical results illustrating the differ- ence between our result and that obtained by using, for ex- ample, the approach used in the ANTENNA code. 5,6 We also explore the moderate magnetic field in detail. In Sec. V, a