Influence of ambipolar potential on the properties of inductively   coupled discharges at the bounce resonance condition
  The importance of accounting for an ambipolar electrostatic potential or a non-uniform density profile for modelling of inductively coupled discharges is demonstrated. A drastic enhancement is observed of the power transfer into plasma for low-collisional, low-pressure, non-local discharges with non-uniform electron density profiles under the condition of bounce resonance. This enhanced plasma heating is attributed to the increase of the number of resonant electrons, for which the bounce frequency inside the potential well is equal to the rf field frequency. 
Oleg V. Polomarov, Constantine E. Theodosiou, and Igor D. Kaganovich