Experience with copper oxide production in antiproton source components at Fermi National Accelerator Laboratory

The Antiproton (Pbar) Source at Fermi National Accelerator Laboratory is a facility comprised of a target station, two rings called the Debuncher and Accumulator and the transport lines between those rings and the remainder of the particle accelerator complex. Water is by far the most common medium for carrying excess heat away from components, primarily electromagnets, in this facility. The largest of the water systems found in Pbar is the 95 degree Fahrenheit Low Conductivity Water (LCW) system. LCW is water which has had free ions removed, increasing its resistance to electrical current. This water circuit is used to cool magnets, power supplies, and stochastic cooling components and typically has a resistivity of 11--18 megaohms-cm. For more than ten years the Antiproton rings were plagued with overheating magnets due to plugged water-cooling channels. Various repairs have been tried over the years with no permanent success. Throughout all of this time, water samples have indicated copper oxide, CuO, as the source of the contamination. Matters came to a head in early 1997 following a major underground LCW leak between the Central Utilities Building and the Antiproton Rings enclosures. Over a span of several weeks following system turn-on, some twenty magnets overheated leading to unreliable Pbar source operation. Although it was known that oxygen in the system reacts with the copper tubing to form CuO, work to remedy this problem was not undertaken until this time period. Leaks, large quantities of make-up water, infrequent filter replacement, and thermal cycling also result in an increase in the corrosion product release rate. A three-pronged approach has been implemented to minimize the amount of copper oxide available to plug the magnets: (1) installation of an oxygen removal system capable of achieving dissolved oxygen concentrations in the parts per billion (ppb) range; (2) regular closed-loop filter/flushing of the copper headers and magnets and stainless steel header during down periods; and (3) installation of a full-flow filtration system designed to remove any CuO produced by the trace amounts of dissolved oxygen in the LCW system. All three items have been completed. The dissolved oxygen concentration is now routinely on the order of 15 ppb and returns to that level within 8--12 hours following an upset condition such as a leak. Prior to installation of the oxygen removal system, oxygen levels were approximately 3,000 ppb. Particle analysis of the water before-and-after filter and flushing of the LCW system indicates a cleaner system. Another round of filter/flushing occurred shortly before the scheduled start-up and will be performed during down periods when deemed necessary by newly-installed instrumentation. The full-flow filtration system has been recently commissioned. The system consists of two parallel filter housings, with a rated total flow capacity of 2,500 gpm at 300 psi, piping to the LCW supply header and associated instrumentation