A network management system communicates with a plurality of intelligent distributed network nodes. When it is expected from the present cycle number that a limit cycle number is exceeded, the bus controller selects a processing level with which the processing is performed with a smaller cycle number, or performs a control of giving no permission to a non-realtime bus access request. Preferably, a spherical electromagnetic confinement field is initiated around the reactor core such that fusion of the nuclear fusionable material generates a plasma which interacts with the spherical electromagnetic confinement field in a magnethydrodynamic manner. The electrode layer is formed on an external surface of the varistor element body by simultaneous firing with the varistor element body.