The design and manufacture of the enhanced radial field amplifier (ERFA) for the jet project

The JET plasma requires a radial magnetic field to control its vertical position and the bulk field is produced using relatively slow (line commutated) amplifiers. Should fast (possibly of order 100 ?s) disturbances arise, the plasma can move from its reference position and this must be controlled using a high-speed amplifier. As part of a wider project to upgrade the plasma control system, a new, more powerful, enhanced radial field amplifier (ERFA) will be installed to replace the existing fast radial field amplifier (FRFA). The company JEMA designed the ERFA to meet the technical requirements specified in the Call-for-tender document and it comprises four series-connected Units with a total rated output voltage of ±12 kV, in 3 kV steps, and a maximum output current of ±5 kA. The ERFA is being manufactured at JEMA's works during 2008 so that it can be installed, tested and then commissioned on the JET radial field load coils in spring 2009.