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