The influence upon diamond film chemical vapour deposition of operator-set process parameters in a novel microwave plasma reactor is examined. The new reactor operates with a discharge sustained by an electromagnetic surface wave in a non-conventional configuration that yields a plasma hemisphere in the vicinity of the substrate. The basic advantages of this reactor compared with "plasma-ball" systems in resonant cavity and bell-jar arrangements have been reported in a previous paper. The present paper provides the results of a parametric study of the quality of diamond films as well as of the gas temperature and hydrogen atom concentration in the discharge as functions of methane and oxygen concentrations, substrate position and temperature, gas pressure, and microwave power density absorbed in the plasma. The conditions optimizing both maximum growth rate and film quality correspond to a total gas pressure of 15 Torr (2 kPa), with a 0.75% CH4 content and a substrate temperature of 930 "C, although good quality films can be achieved over a broader range, at gas pressures between 10 and 60 Torr (1.33-8 kPa), with a 0.25-0.75% CH4 content, and with substrate temperatures in the range 870-980 degrees C.