The grid electrode is curved along a short side direction thereof and includes {HEAD ~ portions} having {TAIL ~ different thicknesses}, the portions being arranged in the short side direction 
having
The grid electrode is curved along a short side direction thereof and includes { HEAD ~ portions } having { TAIL ~ different thicknesses } , the portions being arranged in the short side direction
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH