PURPOSE: To obtain a long electron beam uniform in output density by narrowing the intervals between both ends of a cathode and a filament as compared with that at the center of the cathode, and making the length of the filament longer than that of the cathode.
CONSTITUTION: Since the length I2 of a filament is longer than that I1 of a cathode, the center of the filament where the temperature distribution is uniform heats the cathode by electron shock, but both ends of the filament at low temperature does not contribute to the heating by electron shock. In short, it functions as a filament only in the area where the temperature distribution is uniform. Furthermore, on both ends of the cathode, the intervals to the filaments are narrower 2 than that of the center, so the quantity of heating by electron shock increases. Therefore, even if heat is conducted to a supporting plate 11, both ends of the cathode never falls to low temperature as compared with the center. Namely, the temperature can be equalized over the whole length the cathode 1.
WAKAMOTO IKUO
KONNO SHIGEO
OTANI TADAYOSHI
MITSUBISHI HEAVY IND LTD
JEOL LTD