A microwave plasma reactor adapted to manufacturing synthetic diamond material via chemical vapour deposition, the microwave plasma reactor comprising: a plasma chamber; a substrate holder disposed in the plasma chamber adapted to support a substrate on which the synthetic diamond material is to be deposited in use; a microwave coupling configuration adapted to feed microwaves from a microwave generator into the plasma chamber; and a gas flow system (112, 122) adapted to feed process gases into the plasma chamber and removing them therefrom; wherein the gas flow system comprises a gas inlet nozzle array comprising a plurality of gas inlet nozzles disposed opposite the substrate holder for directing process gases towards the substrate holder, the gas inlet nozzle array comprising: at least six gas inlet nozzles disposed in a substantially parallel or divergent orientation relative to a central axis of the plasma chamber; and a nozzle area ratio of equal to or greater than 10, wherein the nozzle area ratio is measured by projecting the nozzles onto a plane whose normal lies parallel to the central axis of the plasma chamber, measuring the total area of the gas inlet nozzle area on said plane, dividing by the total number of nozzles to give an area associated with each nozzle, and dividing the area associated with each nozzle by an actual area of each nozzle; and characterised by a gas inlet nozzle number density equal to or greater than 5 nozzles/cm 2, wherein the gas inlet nozzle number density is measured by projecting the nozzles onto a plane whose normal lies parallel to the central axis of the plasma chamber and measuring the gas inlet number density on said plane; wherein the gas inlet nozzle number density and the nozzle area ratio are calculated over at least 50% of all the gas inlet nozzles in the gas inlet nozzle array. a plasma chamber; a substrate holder disposed in the plasma chamber adapted to support a substrate on which the synthetic diamond material is to be deposited in use; a microwave coupling configuration adapted to feed microwaves from a microwave generator into the plasma chamber; and a gas flow system (112, 122) adapted to feed process gases into the plasma chamber and removing them therefrom; wherein the gas flow system comprises a gas inlet nozzle array comprising a plurality of gas inlet nozzles disposed opposite the substrate holder for directing process gases towards the substrate holder, the gas inlet nozzle array comprising: at least six gas inlet nozzles disposed in a substantially parallel or divergent orientation relative to a central axis of the plasma chamber; and a nozzle area ratio of equal to or greater than 10, wherein the nozzle area ratio is measured by projecting the nozzles onto a plane whose normal lies parallel to the central axis of the plasma chamber, measuring the total area of the gas inlet nozzle area on said plane, dividing by the total number of nozzles to give an area associated with each nozzle, and dividing the area associated with each nozzle by an actual area of each nozzle; and at least six gas inlet nozzles disposed in a substantially parallel or divergent orientation relative to a central axis of the plasma chamber; and a nozzle area ratio of equal to or greater than 10, wherein the nozzle area ratio is measured by projecting the nozzles onto a plane whose normal lies parallel to the central axis of the plasma chamber, measuring the total area of the gas inlet nozzle area on said plane, dividing by the total number of nozzles to give an area associated with each nozzle, and dividing the area associated with each nozzle by an actual area of each nozzle; and characterised by a gas inlet nozzle number density equal to or greater than 5 nozzles/cm 2, wherein the gas inlet nozzle number density is measured by projecting the nozzles onto a plane whose normal lies parallel to the central axis of the plasma chamber and measuring the gas inlet number density on said plane; wherein the gas inlet nozzle number density and the nozzle area ratio are calculated over at least 50% of all the gas inlet nozzles in the gas inlet nozzle array.