According to an aspect of the invention, there is provided a grid electrode that is substantially thin plate shaped and that includes {HEAD ~ an opening section} having {TAIL ~ plural openings} and a frame section that surrounds the opening section 
According to an aspect of the invention , there is provided a grid electrode that is substantially thin plate shaped and that includes { HEAD ~ an opening section } having { TAIL ~ plural openings } and a frame section that surrounds the opening section
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 HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH