The third form is that the cathode has a heater so that the cathode temperature is controlled in {HEAD ~ a range} of the room temperature to {TAIL ~ about 100 degrees Celsius} to regulate an amount of electron emission from the cathode 
to
The third form is that the cathode has a heater so that the cathode temperature is controlled in { HEAD ~ a range } of the room temperature to { TAIL ~ about 100 degrees Celsius } to regulate an amount of electron emission from the cathode
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 OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH