This embodiment differs from the first embodiment in that there is no takeoff electrode while {HEAD ~ the cathode} 14 has {TAIL ~ a heater} 56 fixed on the back of the cathode 14 
This embodiment differs from the first embodiment in that there is no takeoff electrode while { HEAD ~ the cathode } 14 has { TAIL ~ a heater } 56 fixed on the back of the cathode 14
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH