• J. T. Bradley III, C. J. Andrews, L. F. Fernandez, M. F. Fresquez, W. Reass, W. Roybal, J. B. Sandoval
  LANL, Los Alamos, New Mexico

The proton beam in the LANSCE accelerator is guided and focused almost exclusively by electromagnets. Magnet hysteresis has had significant impacts on the tuning of the LANSCE accelerator.* Magnet hysteresis can also have an impact on Magnet Power Supply (MPS) control, regulation and repeatability requirements. To date, MPS performance requirements have been driven by the requirements on the magnetic fields as determined by the accelerator physicists. Taking hysteresis effects into account can significantly change MPS requirements, as some requirements become more stringent and some are found to be overspecified. Overspecification of MPS requirements can result in significant increases in MPS cost. Conversely, the use of appropriate MPS requirements can result in significant cost savings. The LANSCE accelerator's more than three decades of operation provide a wide variety of magnet power supply technologies and operational experience. We will survey the LANSCE magnet power supply history and determine how performance specifications can be refined to both reduce costs and improve the operators abilities to control the magnetic fields.

*R. McCrady, "Mitigation Of Magnet Hysteresis Effects at LANSCE", LINAC 2006, August, 2006.

• W. Reass, R. F. Gribble
  LANL, Los Alamos, New Mexico

The converter-modulator is a resonant power conditioning configuration that is optimized for a particular load impedance or parameter space. Although traction motor IGBT's are typically used for hard-switching application in the 1 kHz regime, the present use of high-power (10 - 15 MW) converter-modulators have used a 20 kHz resonant switching topology. This presents design challenges to maintain efficient and reliable switching characteristics for the IGBT's. Improved tuning methods and circuit topological changes now offer a significant reduction in IGBT switching losses as compared to those used with the Spallation Neutron Source (SNS) design (perhaps by 10). These circuit and topology changes should also permit Pulse Width Modulation (PWM) of the modulator output voltage to provide a regulated voltage without anomalous IGBT switching characteristics. This paper will review the results of this investigation based on models developed from the SNS converter-modulator operational data.

• W. Reass, D. Rees
  LANL, Los Alamos, New Mexico
• V. P. Derenchuk, T. Rinckel, G. Visser
  IUCF, Bloomington, Indiana

This paper describes the Klystron RF systems for the Indiana University Low Energy Neutron Source (LENS) accelerator 425 MHz Radio Frequency 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 ADC. Four input and two output channels are integrated into a 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.

• W. Reass
  LANL, Los Alamos, New Mexico
• C. Adolphsen, T. G. Beukers, C. Burkhart, R. L. Cassel, M. N. Nguyen, G. C. Pappas, R. Swent, A. C. de Lira
  SLAC, Menlo Park, California
• D. E. Anderson
  ORNL, Oak Ridge, Tennessee

To facilitate a rapid response to the International Linear Collider (ILC) L-Band development program at SLAC, a spare converter-modulator was shipped from Los Alamos. This modulator was to be a spare for the Spallation Neutron Source (SNS) accelerator at ORNL. The ILC application requires a 33% higher peak output power (15 MW) and output current (130 Amp). This presents significant design challenges to modify the existing hardware and yet maintain switching parameters and thermal cycling within the semiconductor component ratings. To minimize IGBT commutation and free-wheeling diode currents, a different set of optimizations, as compared to the SNS design, were used to tune the resonant switching networks. Additional complexities arose as nanocrystalline cores with different performance characteristics (as compared to SNS), were used to fabricate the resonant "boost" transformers. This paper will describe the electrical design, system modifications, modeling efforts, and resulting electrical performance as implemented for the ILC L-band test stand.

• D. Rees, G. O. Bolme, J. T. Bradley III, S. Kwon, J. T.M. Lyles, M. T. Lynch, M. S. Prokop, W. Reass, K. A. Young
  LANL, Los Alamos, New Mexico