in each the plasma generation chamber is indicated at 15 and the process chamber is indicated at 16 a workpiece support is provided at 17 and a workpiece 18 sits thereon the plasma generation or source region is indicated at 19 conveniently the chamber 15 is made of an electrically insulating material and this helps to ensure there is no electrically conductive path that bypasses the convergent field in fig5 an antenna 20 is driven by a rf power supply 21 whilst in fig6 microwave power 26 is supplied to a wave guide 22 and enters the chamber 15 through a window 23 the general construction and operation of such apparatus is well known in the art and further reference can be made to the earlier specifications mentioned above which are incorporated for that purpose by reference 0066 fig7 shows a variation on the apparatus of fig5 this apparatus is intended to provide a supply of purely neutral particles e g free radicals to the process chamber 16 in this arrangement there is also a convergent field at the downstream end of the plasma chamber 15 which in the schematically shown view is produced by coil 4 coil 2 is omitted for clarity sake but as has already been indicated particular magnetic field arrangements can be achieved with coils or permanent magnets working in combination with the arrangement shown in fig7 electrons are reflected at each end of the plasma generation chamber 15 at respective locations a and b this chamber is of insulating material and so there is no path for the electrons to escape ions are therefore also trapped within the chamber 15 a gas feed 24 is provided at the top.