Input impedance of a powerful single-core ferromagnetic inductively coupled plasma source

An experimental study of the recently developed version of the ferromagnetic inductively coupled plasma source has shown that under certain circumstances its input impedance becomes almost independent of the delivered rf driving power and (therefore) of the produced plasma density. This plasma source consists of a large ferromagnetic core, which is fully immersed in plasma. This core is surrounded by a primary winding and plasma appears due to gas discharge driven by an rf voltage applied to this primary winding. We have found values of parameters which determine the input impedance in such an "independent" regime and derived a quantitative theory which is in good agreement with the measured impedance values.