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