The second form is that an electron emission source is disposed behind the cathode and the electron emission source emits electrons which collide against the back of {HEAD ~ the cathode} so that the cathode temperature is controlled in {TAIL ~ a range} of the room temperature to about 100 degrees Celsius to regulate an amount of electron emission from the cathode 
The second form is that an electron emission source is disposed behind the cathode and the electron emission source emits electrons which collide against the back of { HEAD ~ the cathode } so that the cathode temperature is controlled in { TAIL ~ a range } of the room temperature to 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH 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