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