A method of manufacturing synthetic CVD diamond material, the method comprising: providing a microwave plasma reactor comprising: a plasma chamber; one or more substrates disposed in the plasma chamber providing a growth surface area over which the synthetic CVD diamond material is to be deposited in use; a microwave coupling configuration for feeding microwaves from a microwave generator into the plasma chamber; and a gas flow system (112, 122) for feeding process gases into the plasma chamber and removing them therefrom, injecting process gases into the plasma chamber; feeding microwaves from the microwave generator into the plasma chamber through the microwave coupling configuration to form a plasma above the growth surface area or below the growth surface area if the microwave plasma reactor is in an inverted arrangement with process gases flowing in an upwards direction; and growing synthetic CVD diamond material over the growth surface area, wherein the process gases comprise at least one dopant in gaseous form, selected from a one or more of boron, silicon, sulphur, phosphorous, lithium and beryllium, the or each dopant present at a concentration equal to or greater than 0.01 ppm, and/or nitrogen at a concentration equal to or greater than 0.3 ppm, characterized in that the gas flow system includes a gas inlet comprising one or more gas inlet nozzles disposed opposite the growth surface area and configured to inject process gases towards the growth surface area, and wherein the process gases are injected into the plasma chamber through the or each gas inlet nozzle with a Reynolds number in a range 1 to 100. providing a microwave plasma reactor comprising: a plasma chamber; one or more substrates disposed in the plasma chamber providing a growth surface area over which the synthetic CVD diamond material is to be deposited in use; a microwave coupling configuration for feeding microwaves from a microwave generator into the plasma chamber; and a gas flow system (112, 122) for feeding process gases into the plasma chamber and removing them therefrom, a plasma chamber; one or more substrates disposed in the plasma chamber providing a growth surface area over which the synthetic CVD diamond material is to be deposited in use; a microwave coupling configuration for feeding microwaves from a microwave generator into the plasma chamber; and a gas flow system (112, 122) for feeding process gases into the plasma chamber and removing them therefrom, injecting process gases into the plasma chamber; feeding microwaves from the microwave generator into the plasma chamber through the microwave coupling configuration to form a plasma above the growth surface area or below the growth surface area if the microwave plasma reactor is in an inverted arrangement with process gases flowing in an upwards direction; and growing synthetic CVD diamond material over the growth surface area, wherein the process gases comprise at least one dopant in gaseous form, selected from a one or more of boron, silicon, sulphur, phosphorous, lithium and beryllium, the or each dopant present at a concentration equal to or greater than 0.01 ppm, and/or nitrogen at a concentration equal to or greater than 0.3 ppm, characterized in that the gas flow system includes a gas inlet comprising one or more gas inlet nozzles disposed opposite the growth surface area and configured to inject process gases towards the growth surface area, and wherein the process gases are injected into the plasma chamber through the or each gas inlet nozzle with a Reynolds number in a range 1 to 100.