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