A 75kW, 915 MHz microwave plasma-assisted chemical vapor depositionsystem was adapted and utilized to scale up production of high-qualitysingle-crystal diamonds at high growth rates. A 300 mm diameter plasmadischarge was achieved with uniform temperature distributions of ±250°C on up to 300 single-crystal diamond substrates. Diamond singlecrystals were synthesized from H2/CH4/N2gas mixtures at pressures between 90 and 180 Torr, with recordedgrowth rates from 10 to 30 μm/h. The source of N2was from vacuum chamber leakage, and it greatly affected synthesischemistry. Optical emission spectroscopy was used to probe the localizedplasma chemistry and plasma uniformity at different gas pressures.Production rates of up to 100 g/day of single-crystal diamonds weredemonstrated, with 25% of the material categorized as colorless. Crystalsup to 3.5 mm in thickness could be produced during a single depositionrun. The quality of the crystals produced was assessed by photoluminescenceand UV–visible absorption spectroscopies. [ABSTRACT FROM AUTHOR]