A High-Voltage Electrolytic Capacitor Bank

For controlled thermonuclear devices of moderate volume employing externally applied magnetic fields, the magnetic energy requirements extend into the megajoule range. A high-voltage series-parallel bank of electrolytic capacitors can supply this energy reliably and inexpensively. The total cost of the bank, including charging supplies, controls, and labor, is less than 14 cents per joule. Required floor space, including access and service area, is about 250 ft
²
/Mj. A 5-kv electrolytic bank storing 150 kj has been in routine operation since 1958, and is currently being extended to 1 Mj. The bank is composed of 80 modular 12.5 kj sections, each module being a 12-by-12 series-parallel array of 1000-μf 450-v, standard electrolytic capacitors. Each module has its own charging, switching, and fault-sensing circuits. Including external voltage dividers and internal leakage current, about 24w/kj is required to maintain the bank at full voltage. Normal one - quarter cycle discharge times are in the millisecond range with repetition rates ranging from one-half to 15 or more per minute, depending on the external circuit. Capacitor life is measured in years, is dependent upon the time required for the electrolyte to dry out, and is virtually unaffected by the operating schedule of the bank. Flexibility in the usage of the bank is ensured by having multiple output-switching ignitrons in each module. Sequencing and control circuitry provides for time-sharing of the bank by up to five users, each having independent control of bank capacity and voltage.