Newly designed field control module for the SNS

Abstract

Spallation Neutron Source has undergone some recent hardware changes. The intended Field and Resonance Control Module (FRCM) design has been re-vamped to minimize functionality and ease implementation. This effort spans a variety of disciplines, and requires parallel development with distinct interface controls. This paper will discuss the platform chosen, the design requirements that will be met, and the parallel development efforts ongoing.The low-level RF (LLRF) control system for the OVERVIEW OF THE NEW FCMPerformance specifications were eased late last year for the LLRF control system for SNS. Physics simulations indicated that the field control requirement could be reduced from from HS%, iA).5" to kl.O%, k1.0". In addition required functions were changed such that onboard processing for resonance control was moved to the crate controller (IOC), as well as feedforward table update and access; fewer RF channels were required (no need to provide for possible beam information via a beam diagnostics channel); no real time data link needed between the control system and the operators; and milch less memory per channel was deemed appropriate. By moving the iterative learning controls onto the IOC as well, we completely eliminated the need for DSPs on the module. A collaborative effort was established between Lawrence Berkely, Los Alamos, and Oak Ridge national labs in order to develop a control system that meets these specifications [I].Due to these relaxed system performance specifications, and a new staged approach to implementation and integration of control system functions, the original complicated, meet-all-performance-specifications-at-once FRCM de-sign has been greatly simplified. The new Field Control Module (FCM) is still a basic VXIbusbased module with multiple daughter cards. The infrastructure for a VXIbus-based RF Control System (RFCS) was already in place at the SNS: VXIbus crates had been purchased and other modules within the system are VXIbus, so it only made sense to remain consistent. However the new FCM has three new daughter cards which minimize the functionality of the FCM; and the implementation of the firmware is in a staged approach where progressive phases will be achieved as the accelerator grows from one cavity to many and functional requirements of the RFCS increase [l]. A block diagram of the module hardware is given in figure I . PRlNTED CIRCUIT CARDS'rhe imis for thc rc-designed FCM is the successful SNS Diagnostics PCI-based clcctronics, specifically the Beam Position Monitors (BPMs) 121. In that vein, we attempted to make use of a'i tnuch of the foundation provided by the l3i;ignosticc HPMs 3s possible. The BPMs have an Analog Front End daughter card nianufacturecl by 'Bergm Instrumentation of France. Likewise, we specified a very similar I L R F AFE for use on the FCM. The BPMs havc a Digital Front End (DFE) proccssing card. We, too, utilize a DFE for providing the analog-to-digital conversion of the input RF and IF signals, as well as for providing an interface to the...

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