Lawrence Berkeley National Laboratory

Thallium arc plasma was investigated in a vacuum arc ion source. As expected from previous consideration of cathode materials in the Periodic Table of the Elements, thallium plasma shows lead-like behavior. Its mean ion charge state exceeds 2.0 immediately after arc triggering, reaches the predicted 1.60 and 1.45 after about 100 microsec and 150 microsec, respectively. The most likely ion velocity is initially 8000 m/s and decays to 6500 m/s and 6200 m/s after 100 microsec and 150 microsec, respectively. Both ion charge states and ion velocities decay further towards steady state values, which are not reached within the 300 microsec pulses used here. It is argued that the exceptionally high vapor pressure and charge exchange reactions are associated with the establishment of steady state ion values.