PURPOSE: To improve insulation between an auxiliary electrode and a connector electrode by providing an alumina porcelain between the opposing electrode and the auxiliary electrode closely to the opposing electrode while providing mica excellent in discharge deterioration proofness closely to the auxiliary electrode.
CONSTITUTION: While arranging an auxiliary electrode 3 on the side of an counter electrode 2, an alumina porcelain 4 is provided between the counter electrode 2 and the auxiliary electrode 3 closely to the counter electrode 2. Further, mica 6 is provided closely to the auxiliary electrode 3 so as to arrange that mica 6 and aforesaid alumina porcelain 4 may mutually contact. Thereby, even when gaseous discharge is generated between the auxiliary electrode 3 and the alumina porcelain 4, an insulating property can be sufficiently maintained between the counter electrode 2 and the auxiliary electrode 3.
OZAKI YUKIO
NAKATANI HAJIME
