Particulate contamination produced during plasma-assisted deposition of amorphous silicon devices can be responsible for reduced quality and yield. The threshold for power formation imposes an upper limit on the rf power and hence the deposition rate. In this work, the parallel-plate capacitor discharge volume is illuminated and global, spatio-temporal powder production is determined visually and from observed modifications to the discharge electrical properties such as the matching condition, the dc self bias and the rf power transfer efficiency. A systematic study has been made of the powder-free operational space as a function of rf power, rf frequency (13.56-70 MHz) and substrate temperature. (author) 6 figs., 18 refs.