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Discussion of the operating characteristics of a three-terminal thin-film SNS Josephson junction whose diameter is much greater than the electron pair coherence length in the N metal. It is shown that a junction of this type is essentially a two-terminal device even though the third terminal of the junction supplies the control current. The mechanism underlying this finding is discussed.
A particular phenomenon of the SNS Josephson junction was investigated; i.e., control by a current entering the normal region and leaving through one of the superconducting regions. The effect of the control current on the junction was found to be dependent upon the ration of the resistances of the two halves of the N layer. A low frequency, lumped, nonlinear model was proposed to describe the electrical characteristics of the device, and a method was developed to plot the dynamic junction resistance as a function of junction current. The effective thermal noise temperature of the sample was determined. Small signal linearized analysis of the device suggests its use as an impedance transformer, although geometric limitations must be overcome. Linear approximation indicates that it is reciprocal and no power gain is possible. It is felt that, with suitable metallurgical and geometrical improvements, the device has promise to become a superconducting transistor.
YBa(2)Cu(3)O(7-delta)/Au/Nb superconductor/normal-conductor/superconductor (SNS) microbridge devices fabricated using now-standard lithographic techniques and edge geometry to define normally conducting links having submicron-by-several-microns cross-sectional dimensions. Edge geometry allows current to flow only in these planes and takes advantage of longer coherence length at critical YBa(2)Cu(3)O(7-delta)/Au/Nb interface. Sensitivity to damage on edge of YBa(2)Cu(3)O(7-delta)/Au/Nb reduced.
Superconductor/normal conductor/superconductor (SNS) microbridge devices with pinhole-defined active regions undergoing development. Device includes thin, electrically insulating layer deposited epitaxially, with controlled formation of pinholes, on one of two superconducting layers. Normally conducting metal deposited epitaxially in pinholes and on insulating layer, forming electrical contact between two superconducting layers. Junction resistances and maximum junction voltages expected to be increased.
High-T(sub c) SNS weak links are expected to prove useful as high frequency sources and detectors. Recent studies with low-T(sub c) Josephson mixers using shunted tunnel junctions at 100 GHz show good initial performance, and modeling suggests that these results should extrapolate to higher frequencies if larger I(sub c)R(sub n) products can be achieved. Progress on this work will be reported.
High-quality superconductor/normal-metal/superconductor(SNS) edge-geometry weak links have been produced on silicon-on-sapphire (SOS) substrates using a new SrTiO(sub 3)/'seed layer'/cubic-zirconia (YS2) buffer system.
The accelerator at the Spallation Neutron Source is currently being upgraded to increase the proton beam power from 1.4 MW to 2.8 MW. About 2 MW will go to the first target station, while the rest will go to the future second target station. The first target station uses a mercury target. When the short proton beam pulse hits it, strong pressure waves are developed inside the mercury and the vessel itself, causing weld failures and cavitation erosion. The pressure wave can be significantly mitigated by injecting small helium bubbles into the mercury. SNS has been injecting helium since 2017 using small orifices but has met challenges in fabrication and operations with them. Thus, for the 2 MW target, swirl bubblers will be used to increase gas injection and improve reliability. A 2 MW prototypical target was built and tested in a mercury process loop available at Oak Ridge National Laboratory. Acrylic viewports on the top of the target were used to determine the bubble size distribution (BSD) generated by the swirl bubblers. It was found that the bubblers were not only capable of generating small bubbles but that the BSD was independent of gas injection rate.
The Controls Group at the Spallation Neutron Source (SNS) is designing a programmable signal processor based credited safety control that calculates pulsed beam power based on beam kinetic energy and charge. The system must reliably shut off the beam if the average power exceeds 2.145 MW averaged over 60 seconds. This paper discusses architecture and design choices needed to develop the system under the auspices of a programmable radiation-safety credit control.
The High-Voltage Converter Modulators (HVCM) used to power the klystrons in the Spallation Neutron Source (SNS) linac were selected as one area to explore machine learning due to reliability issues in the past and the availability of large sets of archived waveforms. Progress in the past two years has resulted in generating a significant amount of simulated and measured data for training neural network models such as recurrent neural networks, convolutional neural networks, and variational autoencoders. Applications in anomaly detection, fault classification, and prognostics of capacitor degradation were pursued in collaboration with the Jefferson Laboratory, and early promising results were achieved. This paper will discuss the progress to date and present results from these efforts.
The H⁻ ion linear accelerator at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory operates with reliability that routinely surpasses 90% during scheduled beam operation. With the ambitious goal of eventually achieving at least 95% availability, several upgrade and improvement projects are ongoing. One such project is the modification of the coaxial couplers that transfer radio frequency (RF) power to the accelerator’s Radio Frequency Quadrupole (RFQ). The proposed modification utilizes stub sections and capacitive coupling to construct a physically separable assembly with DC isolation. With a separated coupler assembly, the section that includes the magnetic coupling loop can be permanently mounted to the RFQ which would eliminate the need to re-adjust the couplers after maintenance activities, upgrades, and repairs. Additionally, the modified design would provide increased multipaction suppression with DC biasing and potentially lower thermal gradients across the device. This paper presents the design and simulation results of the project.
The research program at the SNS Beam Test Facility is focused on resolving observed model/measurement discrepancies that preclude accurate loss prediction in high-power linacs. The current program of study is focused on deploying direct 6D measurements to reconstruct a realistic model of the initial beam distribution at the RFQ output. This detailed characterization also provides an opportunity for benchmark of RFQ simulations. Here we compare PARMTEQ predictions against 5D-resolved (x, x’, y, y’, dE) phase space measurements of the BTF H⁻ bunch, focusing on the transverse distribution. This work is an extension of [1], which focused on the longitudinal phase space.
The SNS Beam Test Facility research program is focused detailed studies of beam distributions for medium-energy ion beams, with the goal of reconstructing realistic 6D bunch distributions to enable halo prediction. For complete characterization of the initial distribution, scan time scales exponentially with scan dimension. Currently, a full 6D measurement with ~10 points across most dimensions requires 30 hours. However, measurement of the 5D distribution f(x, x’,y,y’,w) can be done very rapidly using a hybrid slit/screen method. This approach requires ~4 hours to obtain at least 32 points/dimension, with very high resolution (0.5 keV) in the energy distribution. This presentation reports on the approach and results for 5D characterization of the initial RFQ-formed bunch. This includes higher-resolution views of previously reported transverse-longitudinal dependence and additional interplane dependencies that were not previously reported.
Co3Sn2S2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Co is bonded in a distorted linear geometry to four Sn and two equivalent S atoms. There are two shorter (2.69 Å) and two longer (2.70 Å) Co–Sn bond lengths. Both Co–S bond lengths are 2.16 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded to six equivalent Co and two equivalent S atoms to form SnCo6S2 hexagonal bipyramids that share corners with six equivalent SnCo6S2 hexagonal bipyramids and edges with six equivalent SnCo6 cuboctahedra. Both Sn–S bond lengths are 2.89 Å. In the second Sn site, Sn is bonded to six equivalent Co atoms to form distorted SnCo6 cuboctahedra that share corners with six equivalent SnCo6 cuboctahedra and edges with six equivalent SnCo6S2 hexagonal bipyramids. S is bonded in a 4-coordinate geometry to three equivalent Co and one Sn atom.
Ni3Sn2S2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ni is bonded in a distorted linear geometry to four Sn and two equivalent S atoms. There are two shorter (2.72 Å) and two longer (2.77 Å) Ni–Sn bond lengths. Both Ni–S bond lengths are 2.18 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded to six equivalent Ni and two equivalent S atoms to form corner-sharing SnNi6S2 hexagonal bipyramids. Both Sn–S bond lengths are 2.91 Å. In the second Sn site, Sn is bonded in a distorted hexagonal planar geometry to six equivalent Ni atoms. S is bonded in a 4-coordinate geometry to three equivalent Ni and one Sn atom.
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Here, residual dose rate measurements were conducted on target vessel #13 and proton beam window #5 after extraction from their service locations. These measurements are used to verify calculation methods of radionuclide inventory assessment that are typically performed for nuclear waste characterization and transportation of these structures. Neutronics analyses for predicting residual dose rates are carried out using the transport code MCNPX and the transmutation code CINDER90. For transport analyses a complex and rigorous geometry model of the structures and their surroundings are applied. The neutronics analyses are carried out using the Bertini and CEM high energy physics models for simulating particles interactions above the table-based cross section range. Finally, obtained calculational results are analyzed and compared to the measured dose rates and overall show good agreement within 25%, which shows applicability of the methods used in analyses.
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