The klystron RF systems for the indiana university lens accelerator
This paper describes the Klystron RF systems for the Indiana University Low Energy Neutron Source (LENS) accelerator 425 MHz radiofrequency quadrupole (RFQ) and drift tube linac (DTL) systems. Of interest in the power conditioning system is the design of the totem-pole grid-catch modulator for the mod-anode klystrons. This topology provides a fast rise and fall and closed loop regulation for the klystron mod-anode to cathode voltage, which minimizes RF amplitude and phase droop while maximizing efficiency. Another advantage is that short pulse high rep-rate operation is viable within the average power capabilities of the klystron. The 425 MHz, 1.25 MW klystron amplifier chain will also be detailed. Of final interest, is the digital low level RF system. This provides vector control of the cavity field using direct conversion, non-I/Q sampling architecture, at a sampling rate of 132 MHz with a 12-bit analog-to-digital converter (ADC). Four input and two output channels are integrated into a 6 unit (6U) VME module, with all DSP functions performed in Xilinx Spartan-3 field-programmable gate arrays. The design and implementation of these systems, coupled with LENS operational results, will be presented.
STATE OF THE ART IN RF CONTROL
Nowadays the designer of a new rf control system has access to a wealth of powerful digital, analog, and rf circuitry. The requirements for the rf control system have changed from only controlling the amplitude and phase of the accelerating field to the required degree to stability. Additional tasks include exception handling and extensive build-in diagnostics while pursuing issues related to reliability, operability, and maintainability. Also operation close to the performance limit must be supported while maximizing the availability of the accelerator. With many accelerator projects in planning or under construction several state-of-the art rf control designs have evolved. This paper will present an overview of this new technology and discuss its performance.
Operational performance of the SNS LLRF interim system
A new approach has been taken to develop and build the Low-Level RF Control System for the SNS Front End and Linear Accelerators, as reported in a separate paper in this conference. An interim version, based on the proven LBNL MEBT design, was constructed to support short-term goals and early commissioning of the Front End RFQ and DTL accelerators, while the final system is under development. Additional units of the interim system are in use at JLab and LANL for concept testing, code development, and commissioning of SNS SRF cryomodules. The conceptual design of the MEBT system had already been presented elsewhere, and this paper will address operational experiences and performance measurements with the existing interim system hardware, including commissioning results at the SNS site for the Front End and DTL Tank 3 together with operational results from the JLab test stand.