An optimized helical resonator which increases the plasma density for efficient processing of semiconductor wafers is characterized by a low inductance and, hence, a low Q. A first embodiment uses either a distributed or lumped capacitance to reduce the value of .omega.L to less than about 200 Ohms. A second embodiment uses a flat spiral coil having a low value of .omega.L and resonant as a 1/4 or 1/2 wave resonator. A third embodiment combines features of the first two embodiments using both spiral and solenoid coils as the helical resonator.