Effects of static magnetic fields on rf-driven plasma sheaths

The physics of sheath formation during rf capacitor discharges in magnetized plasmas is examined, for arbitrary angle between the dc magnetic field and the oscillating rf electric field. Observations from particle simulations show that the induced dc sheath potential under given rf drive increases with increasing angle between the electric and magnetic fields, reaching a maximum nearly twice the unmagnetized dc potential for nearly perpendicular E and B. Analytic study of the ion dynamics in the time-averaged sheath field reveals that the ion motion is unstable, yielding unbound ion transport across the magnetic lines. The effective ion mass m*, employed for the acceleration along the electric field, is obtained as a function of the magnetic angle and the relative magnetic strength. The magnetized presheath ions are partially demagnetized inside the sheath. The ratio of the effective masses mB/m*, where mB stands for fully magnetized ions, parametrizes the sheath potential and sheath thickness. The sheaths behave as unmagnetized in the limit of parallel E and B. copyright 1996 American Institute of Physics