A large graphite or refractory metal cylinder, held above the pool by an insulated electrical connection, serves as the anode. An igniting electrode (called the ignitor), made of a refractory semiconductor material such as silicon carbide,[1] is briefly pulsed with a high current to create a puff of electrically conductive mercury plasma. The plasma rapidly bridges the space between the mercury pool and the anode, permitting heavy conduction between the main electrodes.