(57) A plasma generated within an induction coil is sampled through a sampler orifice
into a first vacuum chamber stage and then through a skimmer orifice into a second
vacuum chamber stage for mass analysis of trace ions in the plasma. Arcing at the
orifices is reduced or prevented by applying, to the plates containing the orifices,
an RF bias voltage derived from the generator which powers the coil. Since optimum
ion transmission is highly dependent on the phase and amplitude of the RF bias, phase
and amplitude adjustment networks are provided to optimize the ion count. Alternatively,
arcing at the sampler orifice can be eliminated by grounding the induction coil at
or near its center and the RF bias can be applied only to the plate containing the
skimmer orifice.
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