source of electric potential not shown for example a dc potential cylindrical magnets designated by reference numeral 217 are utilized to control the plasma generated at the arc forming section the magnets maintain the plasma within a narrow column until the plasma reaches the deposition region 60 optional cooling coils 234 in which a coolant can be circulated can be located within the magnets in operation a mixture of hydrogen and methane is fed to the injector 295 and a plasma is obtained in front of the arc forming section and accelerated and focused toward the deposition region the temperature and pressure at the plasma formation region are typically in the approximate ranges 1500 15 000 degrees c and 100 700 torr respectively and in the deposition region are in the approximate ranges 800 1100 degrees c and 0 1 200 torr respectively as is known in the art synthetic polycrystalline diamond can be formed from the described plasma as the carbon in the methane is selectively deposited as diamond and the graphite which forms is dissipated by combination with the hydrogen facilitating gas for further description of plasma jet deposition systems reference can be made to u s pat no s 4 471 003 4 487 162 and 5 204 144 the bottom portion 105 a of the chamber has a base 106 on which can be mounted a substrate 10 on which the synthetic diamond is to be deposited if desired the substrate can be a tool surface or tool insert on which.