Apparatuses and methods are provided that, in some embodiments use an adjustable middle coil to tune plasma density in a plasma processing system. For example, in one embodiment, a plasma processing apparatus includes an impedance match circuit coupled to an Rf power source. The impedance match circuit measures voltage and current at an inner and an outer coil. The match circuit calculates plasma density from the measured voltage and/or current. An adjustable middle coil located between the inner and outer coils is adjusted and/or replaced to tune the plasma density radial profile.