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The AT-HVCM, achieved by series-stacking the dual-function resonant filter capacitors following each rectification stage, is the baseline design for the PPU project at the SNS [1]. The project requires three AT-HVCM modulators to power 28 additional 700kW klystrons and associated high beta cavities to accelerate 38mA of beam current to 1.3GeV. Each modulator produces an 82 kV, 120A output pulse of 1.35ms duration at a 60Hz repetition rate. The AT design approach improves upon the existing HVCM topology, reducing stresses on the H bridge IGBTs using zero voltage (ZVS) and current switching (ZCS) techniques and on the resonant filter capacitors by limiting voltage reversal. This paper reviews the prototype development progress, currently focused on evaluating system reliability, and discusses some design techniques to achieve the modulator performance requirements.

The High Voltage Convertor Modulators are used to power the RF klystrons used throughout the linear accelerator at the Spallation Neutron Source. The output voltage of the modulator has significant voltage droop and ripple which, combined with low level RF system limitations, affect performance and stability of the accelerator cavities. In conjunction with the progress in the development of the new controller, different modulation techniques were implemented and studied on the test modulator rated at 75 kV, 125 A. This paper presents experimental results from implementation of frequency sweep, phase sweep and combined phase and frequency sweep modulation on the modulator output voltage pulse. Thermal measurements were carried out to determine the effect of these modulations schemes on long term reliability of the modulator. Future plans are also discussed.

The proposed Second Target Station (STS) increases the beam energy at the SNS to 1.3 GeV by adding 7 additional cryomodules (28 cavities) to the end of the existing linear accelerator. To achieve the required gradients, these cavities will be powered with up to 700 kW peak power utilizing upgraded 550 kW klystrons. To meet the additional peak power needs, an enhancement to the present High Voltage Converter Modulator (HVCM) topology is being investigated. A discussion of the benefits derived from this alternate topology will be combined with experimental data from a prototype at SNS.

Three IGBT H-bridge switching networks are used in each High Voltage Converter Modulator (HVCM) system at the Spallation Neutron Source (SNS) to generate drive currents to three boost transformer primaries switching between positive and negative bus voltages at 20 kHz. Every switch plate assembly is tested before installing it into an operational HVCM. A Single Phase Test Stand has been built for this purpose, and it is used for adjustment, measurement and testing of different configurations of switch plates. This paper will present a description of the Test Stand configuration and discuss the results of testing switch plates with two different types of IGBT gate drivers currently in use on the HVCM systems. Comparison of timing characteristics of the original and new drivers and the resulting performance reinforces the necessity to replace the original H-bridge network drivers with the upgraded units.

The High Voltage Converter Modulator (HVCM) systems at the Spallation Neutron Source (SNS) are the primary power sources for the klystrons that supply RF power to the H-beam. The availability of the HVCMs exceeds 99% due to numerous improvements that have been implemented since SNS operations began in 2006. However, the HVCMs continue to operate in open-loop mode that results in significant voltage droop within each pulse. Control margin in the low-level RF control system is becoming a limitation as beam intensity and pulse length are increased to raise the beam power on target to 1.4 MW. This paper will discuss recent progress towards improving the pulse characteristics delivered by the HVCM systems and additional steps being pursued to further improve the system reliability. Alternative modulation schemes for switching the IGBTs, alternative system topologies and various enabling technologies to accomplish these goals will be the primary focus. The motivation, design details, test results and implementation will be presented.

The High Voltage Converter Modulators (HVCMs) are used to power the RF klystrons used throughout the accelerator systems at Spallation Neutron Source (SNS). The output voltage of the HVCM has significant droop and ripple which, combined with low level RF (LLRF) system limitations, affect performance and efficiency of accelerator cavities. In conjunction with the progress in development of the new HVCM controller, different pulse modulation techniques were implemented and studied on the test modulator. This paper discusses the results of implementation of frequency modulation and phase modulation on output voltage. Operational data, including full average power operation, of test modulator is also discussed. Future plans for the new modulation scheme will be presented.

This paper discusses the topology used in the HVCMs at SNS to process power for both the cold and warm linac sections of the klystron gallery in support of extended operations at the megawatt level. In anticipation of a second target station and higher anticipated power levels, an enhancement to the present topology is being investigated. SPICE circuit simulations and preliminary experimental data will be presented.

The SNS at ORNL has been fully operational since 2006 and in September 2009, the design goal of 1 MW of sustained beam power on target was achieved. Historically, the high voltage converter modulators (HVCM) have been a known problem area and, in order to reach another SNS milestone of ≥90% availability, a new gate driver was one of several areas targeted to improve the overall reliability of the HVCM systems. The drive capability and fault protection of the large IGBT modules in the HVCM were specifically addressed to improve IGBT switching characteristics and provide enhanced troubleshooting and monitoring capabilities for the critical IGBT/driver pair. This paper outlines the work involved; the result obtained and documents the driver's long-term performance. Enhanced features, designed to be used in conjunction with a new controller presently under development, will also be discussed.

D.C. multimeter, frequency sweeper and network analyzer. The circuit editor, which allows schematic entry, the above instruments and the analysis to be performed whether it be time domain, frequency domain or dc are all set up using a mouse and menu selections. The work bench offers a large model library, a parametric plotter and two statistical packages to boost engineering productivity. Some of its capabilities will be reviewed in the context of this paper. For the Spice connoisseur, the work bench will soon support Spice Plus, a C based version of Berkley 2G.6, which promises a 1.4X to 2.OX speed enhancement. To the first time user I would suggest he become familiar with Tnum, RELTOL, ABSTOL and VNTOL in the Analysis Options menu. Tnum defines the number of steps during the simulation. The default values for ABSTOL (absolute surrent error tolerance) and VNTOL (absolute voltage error tolerance) are 1.0E-12 and 1.0E-6 respectively and the author is not aware of too many power supply applications that require that kind of convergence accuracy.