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.

HVCM topology enhancements to support a power upgrade required by a second target station (STS) at SNS

The purpose of the Matter-Radiation Interactions in Extremes (MaRIE) facility at Los Alamos National Laboratory is to investigate the performance limits of materials in extreme environments. The MaRIE facility will utilize a 12 GeV linac to drive an X-ray Free-Electron Laser (FEL). Most of the same linac will also be used to perform electron radiography. The main linac is driven by two shorter linacs; one short linac optimized for X-FEL pulses and one for electron radiography. The RF systems have historically been the one of the largest single component costs of a linac. We will describe the details of the different types of RF systems required by each part of the linacs. Starting with the High Power RF system, we will present our methodology for the choice of RF system peak power and pulselength with respect to klystron parameters, modulator parameters, performance requirements and relative costs. We will also present an overview of the Low Level RF systems that are proposed for MaRIE and briefly describe their use with some proposed control schemes.

An Overview of the MaRIE X-FEL and Electron Radiography Linac RF Systems

The targeted beam availability at Department of Energy’s Spallation Neutron Source (SNS) user facility is greater than 95%. The High Voltage Converter Modulators (HVCMs) that are used to power the linac klystrons have been one source of lost beam time. In this work, we explore the use of machine learning (ML) methods to address two problems in HVCMs to improve their reliability. First, prediction of aging and failure of HVCM components such as capacitors, rectifier assemblies containing hundreds of diodes, and insulating oil, in order to preemptively schedule maintenance and replacement. Second, automated tuning of the HVCM operation after service. The ML methodology pursued includes feature extraction, anomaly detection, and autoencoder network learning. The preliminary result indicates that ML can provide advance notice of upcoming faults. Our future work includes the improvement of anomaly prediction rate and HVCM component health state estimation and HVCM autonomous re-tuning.

Machine Learning for Improved Availability of the SNS Klystron High Voltage Converter Modulators

The Spallation Neutron Source (SNS) has been in operation since 2006 and routinely operates at 1 MW of beam power. At 1 MW, the High Voltage Converter Modulators (HVCMs) are delivering 8-11 MW pulsed power to the Klystrons for up to 1185 us at 60 Hz. The pulsed output of the modulator has a substantial voltage droop operating in open-loop mode. Achieving 1.4 MW operations require an increase in the output pulse width of the HVCM, resulting in loss of LLRF control margin due to modulator voltage reduction at the end of the pulse. Initially, the HVCM was designed with a pulse width modulation scheme for droop compensation but early operations at full duty revealed this technique unreliable. Increasing the output voltage of the modulator would likely compromise system reliability. This paper proposes the use of alternate modulation schemes to address the voltage droop. The effect of frequency modulation and phase modulation on voltage droop is studied. Experimental results will also be presented.

Droop compensation for the high voltage converter modulators at the spallation neutron source

SNS electrical systems have been operational for 4 ½ years. System availability statistics and improvements are presented for AC electrical systems, DC and pulsed power supplies and klystron modulators.

Oak ridge national laboratory spallation neutron source electrical systems availability and improvements

Fourteen High Voltage Converter Modulators (HVCM) were initially installed at the Spallation Neutron Source Linear Accelerator (SNS Linac) at the Oak Ridge National Laboratory in 2005. A fifteenth HVCM was added in 2009. Each modulator provides a pulse of up to 140 kV at a maximum width of 1.35 msec. Peak power level is 11 MW with an 8% duty factor. The HVCM system must be available for neutron production (NP) 24/7 with the exception being two, 6-week maintenance periods per year. HVCM reliability is one of the most important factors to maximize Linac availability and achieve SNS performance goals. During the last few years several modifications have been implemented to improve the overall system reliability. This paper presents operational history of the HVCM systems and examines failure mode statistical data since the modulators began operating at 60 Hz. System enhancements and upgrades aimed at providing long term reliable operation with minimal down time are also discussed in the paper.

Sns linac modulator operational history and performance

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Sns linac modulator operational history and performance