PROBLEM TO BE SOLVED: To prevent the effects of magnetic field in the radial direction, the effects of electric field generated by an electrode and the effects of released gas from a permanent magnet by arranging a positive electrode between two negative electrodes, and forming the positive electrode from a magnet wherein a center hole and at least two holes, which are arranged at an equal angular interval with respect to the center hole and have the same inside diameter. ;SOLUTION: Each negative electrode 1 is equipped with an opening 1a at its center, and a positive electrode 2 is so formed as to have a center hole 2a and multiple holes 2b which are arranged at an equal angular interval on the same circumference in the radial direction from the center axis of the center hole 2a and extend vertically, and to impart the same inside diameter for the holes 2b. The positive electrode 2 is composed as a multi-cell anode, the multiple holes 2b are arranged at an equal angular interval on the same circumference in the radial direction from the center axis line of the center hole 2a, a conductive porous shield cylindrical member 3 formed from a nonmagnetic material is inserted into the center hole 2a concentrically with the center axis of the center hole 2a, and the inside surface of the holes 2b and the like are covered with a conductive non-magnetic material 4 or the like.;COPYRIGHT: (C)1999,JPO
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