Radially localized helicon modes in nonuniform plasma

A radial density gradient in an axisymmetric cylindrical plasma column form s a potential well for nonaxisymmetric helicon modes (m not equal 0). This paper presents an analytic description of such modes in the limit of small longitudinal wave numbers. The corresponding mode equation indicates the po ssibility of efficient resonant absorption of rf power in helicon discharge s at unusually low frequencies.