Measurement of transient sputtering of Mo and W by Al and B ions injected by laser ablation in PISCES-A

The development of a transient sputtering technique in PISCES-A plasmas is reported. A Nd:YAG laser is used to ablate impurities from a sample placed outside the plasma column, delivering a short (∼10 μs) pulse of impurities into the plasma. The injected impurity ions travel down the plasma column and cause a brief (∼10-100 μs) pulse of line emission from sputtered target material. This technique offers some advantages over steady-state sputtering experiments: a wide range of impurity ions can be injected, and incoming impurity ion and sputtered atom velocities can be inferred from time of flight measurements. Measurements of Mo and W sputtering by Al2+ and B+ ions are presented. The Mo sputtering yields are found to be about 5-10 times lower than expected, consistent with steady state measurements of sputtering of Mo by He+ under the same conditions. W sputtering is also lower than predicted.