High resolution current control from switched mode power supply

The Argonne Tandem Linac Accelerator System (ATLAS) has been a National User Facility since 1985. Since the commissioning of the Californium Rare Isotope Breeder Unit (CARIBU) in 2012, it has used 2 bespoke water-cooled linear power supplies to allow for milliamp control of the isobar separator magnets, which allows for milligauss control of the magnets. During the upgrade to nuCARIBU, the aging linear power supplies were replaced with off-the-shelf (OTS) switched mode power supplies (SMPS). The benefit of the SMPS is higher efficiency and since they are air-cooled, no load on the water cooling system, while the detriment is the decrease in resolution of the current control. To overcome this limitation, a device was constructed that allows control of a sub-milliamp constant current sink, which is placed in parallel to the magnet. This arrangement allows the control system to “leak” a precise amount of current away from the magnet, effectively giving sub-milliamp control of the current going into the magnet.