Measurements and code comparison of wave dispersion and antenna radiation resistance for helicon waves in a high density cylindrical plasma source

Helicon wave dispersion and radiation resistance measurements in a high den sity (n(e) approximate to 10(19) -10(20) m(-3)) and magnetic field (B < 0.2 T) cylindrical plasma source are compared to the results of a recently dev eloped numerical plasma wave code [I. V. Kamenski and G. G. Borg, Phys. Pla smas 3, 4396 (1996)]. Results are compared for plasmas formed by a double s addle coil antenna and a helical antenna. In both cases, measurements revea l a dominance of the m = +1 azimuthal mode to the exclusion of most other m odes; in particular, no significant m = -1 mode was observed. The helical a ntenna, designed to launch m<0 and m>0 modes in opposite directions along t he field, resulted in an axially asymmetric discharge with very little plas ma on the m<0 side of the antenna. For both antennas, good agreement of the antenna radiation resistance and wave dispersion with the model was obtain ed. It is concluded that unshielded antennas formed from current loops with an important \m\ = 1 component for the conditions of our experiment, coupl e most of their power to the m = +1 helicon mode and thus have negligible p arasitic, nonhelicon plasma loading. This result greatly simplifies calcula tions of power balance in these sources by identifying the helicon as the m ode by which energy is transferred to the plasma. (C) 1999 American Institu te of Physics. [S1070-664X(99)02902-X].