Examination of the Damage to a Graphite Probe Cap Exposed to Rf Heating in Plt Plasmas ^a)

Visual observations, optical microscopy, and Auger spectroscopy are used to determine the effects of ion gyroradii, arcing, sputtering, and/or evaporation caused damage to a probe cap that has been exposed to 460 rf heated PLT plasmas. Arc tracks are seen on the cap, many starting on the ion side at the face of the cap extending upwards and backwards. Calculations are made to determine whether the observed quantity of material lost from the top leading edge of the cap is due to evaporation. Model calculations of the observed damage support the suggestion that the majority of effects are due to synergism between thermalized plasma and fast ions.