throat alternatively the target may be formed as a cylindrical hollow cathode with the plate partially closing the circular throat a rotating asymmetric roof magnetron may be combined with a hollow cathode without the restricting plate application_number US 9616802 A description in one embodiment of the invention illustrated in the cross sectional view of the entire reactor 40 in fig3 and in the more detailed cross sectional view of an inventive target 110 in fig4 the target 110 includes an annularly arranged vault 112 similar to the vault 44 of fig1 however an annular outerly radially extending portion 116 of the target 110 partially closes the vault 112 at its bottom or throat 114 facing the wafer 22 and is electrically fixed to the remainder of the target 110 in this embodiment the radially extending portion 116 is located on only one side the radially inner side of the throat 114 the radially extending portion 116 will be referred to as a throat ring 116 which in the illustrated embodiment produces an annular throat 114 that is symmetric about the center axis 14 but is radially asymmetric with respect to the two sidewalls 46 48 the throat ring 116 is preferably composed of the same material as the rest of the target 110 for example copper with less than 10 wt of alloying elements such as silicon or magnesium preferably the throat ring 116 causes the throat 114 to have an area extending circumferentially around the vault 112.