22 23 for which purpose claws 63 66 at the ends of the bars facing away from the base portions are also designed to engage rear plates 41 42 each of which is otherwise connected by screws 67 68 to the magnetic yokes to connect targets 49 50 rigidly to magnetic yokes 22 23 clamping screws 69 70 which connect wedge jaws 71 72 73 74 together are screwed in against blocks 44 47 until rear plates 41 42 rest firmly against upper edges 63 66 at the top and lower claws 59 62 rest firmly against spacer bars 75 78 at the bottom so that all of the parts gripped by clamping bars 37 40 are connected rigidly together because pillow blocks 13 14 are rigidly connected to magnetic yokes 22 23 by means of screws 20 21 24 25 the yokes are supported by upper wall section 5 of vacuum chamber 6 at the same time cover plate 79 is supported on insulators 81 82 which are held in place in turn by screws 20 21 24 25 because a gap 83 is provided between pillow block 13 and insulator 15 cathodes 3 4 can execute a certain relative motion in the horizontal plane with respect to the means of suspension shown on the right in fig2 because insulators 15 16 are connected to pillow blocks 13 14 in an articulated.