FIG 4 is {HEAD ~ a cross sectional view} of {TAIL ~ an electron gun unit} of the third embodiment 
FIG 4 is { HEAD ~ a cross sectional view } of { TAIL ~ an electron gun unit } of the third embodiment
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH