The SNS Linac RF Control System

The SNS linac RF control system (RFCS) is currently in development. A system is being installed in a superconducting test stand at Jefferson Laboratory presently. Two systems will soon be installed at Oak Ridge National Laboratory (ORNL) and more are due to be installed early next year. The RF control system provides field control for the entire SNS linac, including an RFQ and 6 DTL cavities at 402.5 MHz as well as three different types of cavities at of 805 MHz: 4 CCL cavities, 36 medium beta superconducting (SRF) cavities, and 45 high beta superconducting cavities. In addition to field control, it provides cavity resonance control, and incorporates high power protect functions. This paper will discuss the RFCS design to date, with emphasis on the challenges of providing a universal digital system for use on each of the individual cavity types. The RF control system hardware has been designed to minimize the amount of changes for all of the applications. Through software/ firmware modification and changing a couple of frequency-dependent filters, the same control system design can be used for all five cavity types. The SNS is the first to utilize SRF cavities for a pulsed highcurrent proton accelerator, thereby making RF control especially challenging. 1 SYSTEM IMPLEMENTATION Figure 1 shows a block diagram of a typical RFCS. The dotted lines represent different VXIbus modules that perform the functions described above. The overall design of the SNS relies on a variety of cavity types as well as RF sources [1]. Due to physical layout constraints, a single VXIbus crates houses a single RFCS for the RFQ, and each DTL and CCL cavity. However, we take advantage of the smaller klystrons and power supply configuration for the SRF sections to increase the number of systems in each crate. For the medium-beta sections, there are typically three RF control systems housed in a single crate, while for the high-beta, two systems per crate are the norm. The VXIbus architecture takes advantage of the backplane in order to stream-line data-acquisition, system-monitoring and real-time-event-processing tasks. The VXIbus serves as an interface for the global experimental physics and industrial control system (EPICS) to send and receive information about the way the RFCS controls the in-phase and quadrature (I/Q), rather than amplitude and phase, components of the accelerator cavity RF field. Σ DIGITAL CONTROL SYSTEM CIRC RF LOAD