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DOE OSTI2022

A realistic guide misalignment model for the Second Target Station instruments at the Spallation Neutron Source

The Second Target Station (STS) at the Spallation Neutron Source, including a suite of initial instrument concepts, are being designed in Oak Ridge. The moderator size at STS is significantly smaller than that of the First Target Station, making the guide misalignment a more prominent concern. Here a realistic misalignment model based on Monte Carlo neutron ray tracing simulation was developed to evaluate the impacts of both the random misalignment and floor settlement on the performance of a toy model of 150 m straight guide system, and MENUS, an STS instrument concept with a typical guide design of two opposing Montel mirrors. The study shows that longer instruments, and instruments with complex curved mirrors/guides are sensitive to significant performance penalties due to misalignments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2017

Record Performance of and Extraction Studies with the Spallation Neutron Source H- Injector

During the past year the Spallation Neutron Source has operated with proton beam powers up to 1.4 MW with good availability. However, after a recent premature target failure the power was reduced to 1 MW for the ~20-week service cycle of the new target, whereas the subsequent target will be used at 1.2 MW. The ion source and low-energy beam transport deliver 50 to 60 mA H- beams into the RFQ with availbilities of ~99.5%. The compromised RFQ transmission limits the LINAC beam to ~35 mA, which is sufficient for 1.4 MW. Our current injector efforts focus on improving reliability and increasing the source service cycles beyond the achived 7 A·h to reduce the venting of the RFQ and to improve the stability of the accelerator operations. In addition, extraction studies show that higher extraction fields improve the RFQ transmission, apparently due to a reduced emittance of the LEBT H- beams.

Stockli, Martin P.↗

DOE OSTI2024

Measurement and modeling of beam transport in the FODO line of the Spallation Neutron Source Beam Test Facility

Ongoing studies at the Spallation Neutron Source (SNS) Beam Test Facility (BTF) seek to understand and model bunch dynamics in a high-power LINAC front-end. The BTF has recently been upgraded with a reconfiguration from a U-shaped line to a Straight line. We report the current state of model benchmarking, with a focus on RMS beam sizes within the FODO line. The beam measurement is obtained via three camera/screen pairs in the FODO line. This presentation discusses the methodology and results of this measurement.

Thompson, Trent↗

DOE OSTI2026

Python-EPICS RF Conditioning Automatic Control System at the Spallation Neutron Source

The RF Test Facility (RFTF) at the Spallation Neutron Source (SNS) is used for the conditioning of RF compo-nents such as ceramic vacuum windows and power cou-plers prior to their installation in the H- ion linear accel-erator. This process exposes components to high-power RF fields and thermal cycling to improve performance and remove surface impurities. To automate and optimize this process, a Python-based EPICS control system was developed alongside targeted hardware upgrades. The system enables real-time monitoring and control of RF power levels, temperature, and vacuum pressure. A user-friendly graphical interface was implemented using CS-Studio (Phoebus), allowing operators to adjust parameters and collect data efficiently. The system integrates a High-Power Protection Module (HPM) for interlocks based on vacuum and arc detection, ensuring safe operation. These upgrades have significantly improved the efficiency, accuracy, and safety of RF conditioning at the SNS RFTF. This paper describes the updated RF conditioning sys-tem, highlighting the software and hardware develop-ments and their application in support of the Proton Pow-er Upgrade (PPU) project.

Lee, Sung-Woo [ORNL] (ORCID:000000030915835X)↗

DOE OSTI2022

Progress on the Proton Power Upgrade Project at the Spallation Neutron Source

The Proton Power Upgrade Project at the Spallation Neutron Source at Oak Ridge National Laboratory will increase the proton beam power capability from 1.4 to 2.8 MW. Upon completion of the project, 2 MW of beam power will be available for neutron production at the existing first target station with the remaining beam power available for the future second target station. The project will install seven superconducting RF cryomodules and supporting RF power systems and ancillaries to increase the beam energy to 1.3 GeV . The injection and extraction region of the accumulator ring will be upgraded, and a new 2 MW mercury target has been developed along with supporting equipment for high-flow gas injection to mitigate cavitation and fatigue stress. Equipment is being received from vendors and partner laboratories, and installation is underway with three major installation outages planned in 2022-2024. The project is planned to be completed in 2025.

43 PARTICLE ACCELERATORS↗

DOE OSTI2013

Experiment Automation with a Robot Arm using the Liquids Reflectometer Instrument at the Spallation Neutron Source

The Liquids Reflectometer instrument installed at the Spallation Neutron Source (SNS) enables observations of chemical kinetics, solid-state reactions and phase-transitions of thin film materials at both solid and liquid surfaces. Effective measurement of these behaviors requires each sample to be calibrated dynamically using the neutron beam and the data acquisition system in a feedback loop. Since the SNS is an intense neutron source, the time needed to perform the measurement can be the same as the alignment process, leading to a labor-intensive operation that is exhausting to users. An update to the instrument control system, completed in March 2013, implemented the key features of automated sample alignment and robot-driven sample management, allowing for unattended operation over extended periods, lasting as long as 20 hours. We present a case study of the effort, detailing the mechanical, electrical and software modifications that were made as well as the lessons learned during the integration, verification and testing process.

automated alignment↗

DOE OSTI2017

Techniques for Achieving High Reliability Operation of the Spallation Neutron Source High Power Radio-Frequency System

The Spallation Neutron Source (SNS) high power radiofrequency (HPRF) system operates with high reliability to support the goals of the SNS user program. In recent operational periods the availability of the HPRF system has exceeded 97 percent while the neutron source availability overall is typically greater than 90 percent. SNS has a unique set of 92 HPRF stations that operate at either 402.5 MHz or 805 MHz with peak output power ranging from 550 kW to 5 MW and average power ranging from 49.5 kW to 450 kW. The HPRF transmitters consist of chassis-mounted power supplies, solid-state amplifiers and other equipment that support the operation of the klystrons that ultimately provide the RF power to the accelerating structures. Management of the operation and maintenance of the HPRF system has increasingly focused on reliability and sustainability in recent years. Techniques for klystron lifetime preservation and optimization of transmitter reliability have been developed and will be described.

Moss, John↗

DOE OSTI2022

Progress on the Proton Power Upgrade Project at the Spallation Neutron Source

Barbier, Charlotte↗

DOE OSTI2021

Progress on the Proton Power Upgrade at the Spallation Neutron Source

The Proton Power Upgrade Project at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory will double the proton power capability from 1.4 to 2.8 MW. This will be accomplished through an energy increase from 1.0 to 1.3 GeV and a beam current increase from 26 to 38 mA. The energy increase will be accomplished through the addition of 7 cryomodules to the linear accelerator (Linac). The beam current increase will be supported by upgrading several radio-frequency systems in the normal-conducting section of the Linac. Upgrades to the accumulator ring injection and extraction regions will accommodate the increase in beam energy. A new 2-MW-capable target and supporting systems will be developed and installed. Conventional facility upgrades include build-out of the existing klystron gallery and construction of a tunnel stub to facilitate future beam transport to the second target station. The project received approval to proceed with construction in October 2020. Procurements are in progress, and some installation activities have already occurred. Most of the installation will take place during three outages in 2022-2023. The project early finish is planned for 2025.

Barbier, Charlotte↗

DOE OSTI2022

Mitigating Cathode Overcurrent Faults at the Spallation Neutron Source

The high-power klystron amplifiers at the Spallation Neutron Source (SNS) have been in operation for over 100,000 hours. Overcurrent faults from the klystron cathodes comprise the bulk of RF System downtime. Reliable operation is of particular interest to the SNS, and data from over a decade of operation is used to help mitigate repetitive overcurrent conditions.

Moss, John↗

DOE OSTI2019

Upgrade of the Spallation Neutron Source Injection and Extraction Kicker Pulse Verification Systems

The Spallation Neutron Source (SNS) injection system transports a chopped, 1ms H- ion beam from the linac into the accumulator ring, where two electrons are stripped from each ion, resulting in a proton beam propagating in the ring. The injection kickers use a 1400A current source with a 1ms discharge time to paint the optimum phase space of the injected proton population. The accumulation ring stacks 1us bunches from the 1ms beam pulse to increase peak beam current by a factor of ~1000. The accumulated beam is deflected by fourteen 33kV, 700ns pulsed extraction kicker magnets and delivered to the mercury target, where neutrons are spalled for science experiments. Protecting the accelerator from an errant beam—which may result from asynchronous firing or insufficient magnetic-field intensity in kicker systems—requires a system that monitors and verifies the pulsed current in the kicker magnets prior to and during each 60Hz beam pulse. In addition, the extraction system pulse-forming network (PFN) is verified to be correctly charged and ready for triggering prior to injecting the beam into the linac from the ion source. This paper describes the two verification systems requirements, limitations of the existing systems, and development of new systems.

Morris, B↗

DOE OSTI2014

Spallation Neutron Source Cryogenic Test Facility Horizontal Test Apparatus Operation

The Spallation Neutron Source (SNS) has built Superconducting Radio Frequency (SRF) processing and testing facilities to support improvement programs and future upgrades. The Cryogenic Test Facility (CTF) system is capable of delivering liquid helium at 4.5K to different test apparatus in support of SRF testing. This paper describes the final stages of fabrication, commissioning and the initial operation of the Horizontal Test Apparatus (HTA). The HTA allows for cold testing of single jacketed medium-beta or high-beta SRF cavities. Heat loads, capacities, and other performance data collected during operation will be presented. Cavity testing lifecycle for plasma processing research and development will be discussed. System changes to allow for 2K helium operation in the HTA will also be addressed.

Afanador, Ralph↗

DOE OSTI2016

Irradiation in the Swiss Spallation Neutron Source and its Applications

In high power (∼ 1 MW or higher) spallation targets being operated or developed for different attractive applications such as neutron scattering science and technology or accelerator driven systems (ADS) for nuclear waste transmutation, both target and structural materials are exposed to intensive irradiation of high energy protons and spallation neutrons. Since spallation reactions induced by high energy protons can produce helium (He) and hydrogen (H) and other transmutation elements at very high rates, the behavior of materials used in a spallation irradiation environment can be much different from those observed from materials irradiated with neutrons in fission reactors. Therefore, the damage induced by spallation irradiation cannot be simply simulated by fission neutron irradiation experiments. Seven irradiation experiments have been conducted in the targets of the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institute (PSI) since 1998 within a broad international collaboration with Commissariat a L'energie Atomique Centre d'Etudes de Saclay (CEA), Forschungszentrum Juelich (FZJ), Japan Atomic Energy Agency (JAEA), Los Alamos National Laboratory (LANL), Oak Ridge National Laboratory (ORNL), University California Santa Barbara (UCSB) and several institutes of Chinese Academy of Sciences. More than 7000 samples from various Al-, Ti-, Fe-, Ni-, Zr-, and W-alloys and SiC/SiC, C/SiC and MAX-phase ceramics composites have been irradiated to doses up to ∼25 dpa (in Fe) and ∼2000 appm He at temperatures up to ∼800 deg. C. In addition, quite many specimens were irradiated in contact with stagnant liquid metals such as Hg, PbBi, PbLi etc. Dedicated post-irradiation examinations (PIE) have been performed, together with the international collaborators. Various mechanical tests including tensile, bend, Charpy-impact, small punch and hardness have been carried out to obtain the mechanical properties of the materials after irradiation. The microstructural changes in the irradiated specimens have been investigated by means of transmission electron microscopy, positron annihilation spectroscopy, atom probe tomography etc. Many novel results have been obtained from the PIE conducted by PSI and other STIP partner laboratories. The DBTT-shift of different FM steels increases more or less linearly with dose after irradiation in the SINQ target, while it saturates at a level of few dpa in fission neutron irradiation cases. This phenomenon can be mostly attributed to helium effects. In addition to the strong embrittlement effect, pronounced hardening effect was also detected in high dose specimens, which was contributed by high density helium bubbles.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Analysis of structure and deformation behavior of AISI 316L tensile specimens from the second operational target module at the Spallation Neutron Source

In an earlier publication, tensile testing was performed on specimens removed from the first two operational targets of the Spallation Neutron Source (SNS). There were several anomalous features in the results. First, some specimens had very large elongations (up to 57%) while others had significantly smaller values. Second, there was a larger than the usual amount of data scatter in the elongation results. Third, the stress-strain diagrams of nominally similar specimens spanned a wide range of behavior ranging from expected irradiation-induced hardening to varying levels of force drop after yield point and indirect signs of "traveling deformation wave" behavior associated with strain-induced martensite formation. To investigate the cause(s) of such variable tensile behavior, several specimens from Target 2, spanning the range of observed tensile behavior, were chosen for detailed microstructural examination using electron backscattering analysis (EBSD). It was also shown that the steel employed in the construction of the target contained an unexpected bimodal grain size distribution, containing very large out-of-specification grains surrounded by necklaces of grains of within-specification sizes. The large grains were frequently comparable to the width of the gauge section of the tensile specimen. Moreover, the propensity to form martensite during deformation was shown to be accelerated by radiation but also to be very sensitive to the relative orientation of the grains with respect to the tensile axis. Specimens having large grains in the gauge that were most favorably oriented for production of martensite strongly exhibited the traveling deformation wave phenomenon, while those specimens with less favorably oriented grains had lesser or no degree of the wave effect, thereby accounting for the larger than expected data scatter.

316L↗

DOE OSTI2024

Assessment of simulated and observed cavitation-induced erosion damage in Spallation Neutron Source target vessels

Cavitation-induced erosion damage in different Spallation Neutron Source (SNS) target designs are simulated using explicit finite element–based techniques and compared with observations of erosion in targets after operation. The efficacy of the previously developed method, called saturation time, was evaluated using erosion-damaged samples from new target designs. A new metric called maximum bubble size was implemented under the rationale that larger cavitation bubbles will collapse more intensely. The maximum cavitation bubble size over 1 ms of simulated time was calculated based on the Rayleigh–Plesset equation for each element integration point and presented as a contour map at the vessel surface for assessing with erosion observations. SNS targets are now operated with helium gas injection to reduce cavitation damage. A simulation method using a material model for the mixture of mercury and gas bubbles was recently developed and used to account for the effect of small gas bubbles on the structural response of the target vessel. Furthermore, this work compares the new method's results with observed cavitation damage. Maps of the calculated maximum bubble size for targets operated with and without gas injection were compared with photographs of erosion damage observed in SNS targets. The patterns in maximum bubble size maps correlated well with observations of erosion patterns in target vessels after service. Advantages and challenges of the maximum bubble size simulation technique are provided, and differences between results from the previous and the newly proposed metric are discussed.

Jiang, Hao↗

DOE OSTI2023

Spallation Neutron Source Hydrogen Relief Analysis for the Cryogenic Moderator System

The Spallation Neutron Source at Oak Ridge National Laboratory operates the Cryogenic Moderator System (CMS) which provides hydrogen cooling at 20K to three neutron moderators. Each hydrogen loop is protected by multiple burst discs and reclosing relief valves. As a result of the Proton Power Upgrade project, the CMS moderator loops will hold more hydrogen and thus require piping modifications. Operational experience has demonstrated that transient pressure increases in these hydrogen loops occasionally result in the rupture of the burst discs. The causes for pressure transients in the system that might lead to hydrogen venting are varied and complex, for example loss of vacuum or cooling. Dynamic simulation and analysis of the parameters considered as the worst-case relief venting scenario were performed and will be presented.

47 OTHER INSTRUMENTATION↗

DOE OSTI2017

Progress on the Proton Power Upgrade of the Spallation Neutron Source

The Proton Power Upgrade Project is underway at the Spallation Neutron Source at Oak Ridge National Labor-atory and will double the proton beam power capability from 1.4 MW to 2.8 MW to provide increased neutron intensity at the first target station and to support future operation of the second target station. This will be ac-complished by increasing the beam energy to 1.3 GeV and the beam current to 38 mA (average during the macropulse). Installation of 28 additional superconduct-ing cavities and their associated technical systems will provide for the energy increase. Increased beam loading throughout the accelerator will be accommodated primar-ily through the use of existing margin in the RF systems and the installation of 700 kW klystrons to power the new superconducting cavities. Upgrades of a few existing RF stations may also be needed. The injection and ex-traction regions of the accumulator ring will be upgraded, a ring to second target station tunnel stub will be con-structed, and a 2 MW target will be developed for the first target station. The project anticipates attainment of Criti-cal Decision 1 in 2017 to ratify the project conceptual design and cost range.

Champion, Mark S↗

DOE OSTI2015

The Macromolecular Neutron Diffractometer MaNDi at the Spallation Neutron Source

The Macromolecular Neutron Diffractometer (MaNDi) is located on beamline 11B of the Spallation Neutron Source at Oak Ridge National Laboratory. Moreover, the instrument is a neutron time-of-flight wavelength-resolved Laue diffractometer optimized to collect diffraction data from single crystals. Finally, the instrument has been designed to provide flexibility in several instrumental parameters, such as beam divergence and wavelength bandwidth, to allow data collection from a range of macromolecular systems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗