A plasma crucible (92) has a through bore (93) and two tubes (981, 982) butt sealed on to the end faces (901, 902) of the crucible. One (981) of the tubes is closed prior to the filling of the crucible. The tube is tipped off and worked in a glass lathe to form it to have a flat end (983). After evacuation, dosing and gas fill, the other tube (902) is tipped off in the similar manner.
展开▼
