3 KA power supplies for the Duke OK-5 FEL wigglers

The next generation electromagnetic OK-5/Duke storage ring FEL wigglers [1], [2] require three 3kA/70V power supplies with current stability about 20 ppm and current ripples less than 20 ppm in their full operating range. Duke FEL Laboratory acquired three out-of-service SCR controlled power supplies (Trans-Rex, 5kA/100V), which were built almost 30 years ago. The existing archaic firing circuit, lack of any output voltage filtering and with an outdated DCCT, would not be able to meet the above requirements. To deliver the desirable high performance with very limited funds, all three Trans-Rex power supplies have been completely rebuilt in-house at DFELL. Modern high stability electronic components and a high precision Danfysik DCCT have been used. A new symmetrical firing circuit, efficient passive filter and reliable transformer-coupled active filter are used to reduce output current ripples to an appropriate level. At the present time, all three refurbished power supplies are in operation. One of these power supplies was used since August, 2004 to feed OK-4 wigglers with good overall performance. Others two have been tested and used as power supplies for magnetic measurements.