The Ipns Rcs Rf System Third Cavity Upgrade*

The IPNS RCS is a rapid cycling synchrotron used to accelerate protons from 50 MeV to 450 MeV, 30 times per second. Currently, two single-gap, ferrite-loaded coaxial cavities, located 180o apart, provide a total peak accelerating voltage of approximately 21 kV over the 2.2 MHz to 5.1 MHz revolution frequency band. An amplifier chain, which includes a 2 kW predriver, a 20 kW driver and a 100 kW final, drives each cavity. A third RF system, consisting of a cavity, cavity bias supply, and amplifier chain, is currently under construction. When complete, this upgrade will provide flexibility in operation that is expected to enhance reliability (i.e., three cavity operation at higher total accelerating voltage, three cavity operation at lower voltage per cavity, or two cavity operation with an on-line spare). In addition, the third cavity will provide an experimental station for second harmonic RF cavity studies. We report progress to date. 1 GENERAL DESCRIPTION The IPNS accelerator operates at an average reliability of greater than 95%. As IPNS approaches 20 years old, facility and equipment aging have become major concerns. To address these concerns in part, and to provide a path for enhancement, an effort is currently underway to upgrade the RCS RF system with the addition of a third accelerating cavity. Figure 1 shows a schematic drawing of the IPNS RCS ring. Figure 1. Schematic diagram of IPNS RCS ring. The existing RF system consists of two single-gap, 50.75” long coaxial ferrite-loaded accelerating cavities, located opposite each other in the L2 and L5 straight sections. A power amplifier chain consisting of a 2 kW predriver, a 20 kW driver and a 100 kW final drive each cavity. The predriver and driver stages, power supplies and local controls are located above the RF stations outside the radiation shield. The final power amplifiers are located beneath the respective cavities. A single 10 kV plate supply, rated at 1 MW, provides power for both final amplifiers, and is housed in a power shed adjacent to the RCS building. Cavity tuning is provided by 1000 A, 30 V variable DC power supplies, coupled to each cavity via a single-turn, figure-eight, water-cooled bias conductor. A variable current of ~100 A to ~800 A provides the saturating field (~1.5Oe to ~11Oe) required to tune each cavity over the 2.2 MHz to 5.1 MHz frequency band[1]. The third-cavity upgrade, when complete, will provide a third accelerating cavity and final power amplifier in the L6 straight section. The final plate supply, cavity bias supply, driver and predriver stages will be located above the L6 section outside of the radiation shield. Progress to date includes initial design of the amplifiers and plate supplies, final plate supply specifications and purchase, predriver construction and initial testing, and driver plate supply construction. 2 ACCELERATING CAVITY The third cavity will be identical to the existing two cavities and will be constructed from spare parts. Figure 2 shows a photograph of an existing cavity with the bias choke box and top shell removed. Figure 2. Existing cavity with the top shell removed. The existing cavities are single-gap, coaxial ferriteloaded, water-cooled structures 50.75” long. Each cavity is made up of two core stack modules that are each 20” long and 13.75” O.D. Each stack module is made up of twenty Phillips type 4H ferrite torroids, twenty-one 0.125” edge-cooled copper cooling disks, insulating end ___________________________________________ *This work is supported by the U.S. Department of Energy under contract no. W-31-109-ENG-38. **[email protected] 0-7803-7191-7/01/$10.00 ©2001 IEEE. 834 Proceedings of the 2001 Particle Accelerator Conference, Chicago