The Oxford folded tandem

The large vertical Van de Graaff in the Nuclear Physics Laboratory at Oxford University has been converted to a folded tandem with a rated terminal voltage of 10 MV. The new parts were designed and largely manufactured within the Laboratory and included the terminal, two negative ion sources, low energy and high energy beam transport and vacuum systems and a new control system. The conversion began in July 1977 and progressed so that experiments with the folded tandem began in January 1979. Excluding the value of manufacture and installation by Laboratory staff, the total cost of the conversion was 100 000 pound, the major items of outside manufacture being the 1800 magnet, the accelerator tubes and the serial data links. The main design features of the new accelerator are discussed as well as its performance during the first 18 months of operation. (orig.)