A reactor includes a plasma duct; a gas inlet, at a distal end of the plasma duct, for receiving a gas; a gas outlet at a proximal end of the plasma duct for removing a portion of the gas to generate a gas flow through the plasma duct; a separating baffle positioned between the plasma duct and the gas outlet for restricting gas flow to maintain high pressure in the plasma duct; a shielded cathodic arc source positioned in a cathode chamber at the proximal end; a remote anode, positioned in the plasma duct, for holding a substrate and cooperating with the cathodic arc source to generate an electron flow opposite the gas flow, to initiate a plasma discharge perpendicular to the remote anode at least in vicinity of the remote anode and deposit ions of the plasma discharge on the substrate to form a diamond coating.