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DOE OSTI2013

Optimal conditions for high current proton irradiations at the university of Wisconsin's ion beam laboratory

The National Electrostatics Corporation's (NEC) Toroidal Volume Ion Source (TORVIS) source is known for exceptionally high proton currents with minimal service downtime as compared to traditional sputter sources. It has been possible to obtain over 150{mu}A of proton current from the source, with over 70{mu}A on the target stage. However, beam fluxes above {approx}1 Multiplication-Sign 10{sup 17}/m2-s may have many undesirable effects, especially for insulators. This may include high temperature gradients at the surface, sputtering, surface discharge, cracking or even disintegration of the sample. A series of experiments were conducted to examine the role of high current fluxes in a suite of ceramics and insulating materials. Results will show the optimal proton irradiation conditions and target mounting strategies needed to minimize unwanted macro-scale damage, while developing a procedure for conducting preliminary radiation experiments.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Support Structure Design of the $\hbox{Nb}_{3}\hbox{Sn}$ Quadrupole for the High Luminosity LHC

New low-β quadrupole magnets are being developed within the scope of the High Luminosity LHC (HL-LHC) project in collaboration with the US LARP program. The aim of the HLLHC project is to study and implement machine upgrades necessary for increasing the luminosity of the LHC. The new quadrupoles, which are based on the Nb₃Sn superconducting technology, will be installed in the LHC Interaction Regions and will have to generate a gradient of 140 T/m in a coil aperture of 150 mm. In this paper, we describe the design of the short model magnet support structure and discuss results of the detailed 3D numerical analysis performed in preparation for the first short model test.

43 PARTICLE ACCELERATORS↗

DOE OSTI2025

Enhancing water and oxygen transport through electrode engineering for AEM water electrolyzers

Anion-exchange membrane water electrolyzers (AEMWEs) can accelerate the deployment of more efficient and affordable hydrogen production solutions. Here, electrode structure is shown to affect water back-diffusion and oxygen transport, which, in return, governs overpotential behaviors in AEMWEs. Measurements indicate that electrode with copious catalytic sites produces water close to the AEM, creating a higher water gradient and driving water back-diffusion, which improves membrane hydration and mass transport. In situ measurement reveals a high pH gradient near the anode surface, which affects anode kinetics. Operando measurement shows reduced oxygen accumulation when decoupling oxygen production and transport on anode. Catalyst ink rheology and stability are tuned with additives to realize scalable fabrication of electrodes with enhanced transport features, allowing AEMWE to operate at 2 A cm−2 for over 1,000+ h at a 2.3 μV h−1 degradation rate. Analysis during and post-durability provides insights into degradation mechanisms. This work demonstrates an electrode design strategy for efficient and durable AEMWEs.

AEM↗

DOE OSTI2011

Fabrication Studies for a Cylindrical DDS Structure at 90 GHz

A natural extension of work on the next generation of high power RF sources and accelerating cavities for Linear Colliders implies cylindrical, damped, detuned structures for millimeter wavelengths. Commercial availability of WR-10 waveguides and other components in the 75-110 GHz range provides a practical goal. Fabrication methods are surveyed, compared and, in some cases, tested to determine whether they can provide the imposed tolerances. Different techniques and tolerances are compared to previous methods at longer wavelengths. The higher gradients and corresponding surface fields indicate that a better understanding of the surface physics is required as well as how the different fabrication steps influence those surface characteristics that impact the final operation. We consider existing systems at SLAC and elsewhere as a function of frequency to determine what is desirable to measure and control for all phases of the fabrication, testing, conditioning and use of these systems. For example, the importance of crystal structure to the different steps is discussed. The preferred method allows a variety of design alternatives to be pursued simultaneously and extends to shorter wavelengths as well as provides possibilities for embedded test and control elements.

43 PARTICLE ACCELERATORS↗

DOE OSTI2017

Incompressible variable-density turbulence in an external acceleration field

Dynamics and mixing of a variable-density turbulent flow subject to an externally imposed acceleration field in the zero-Mach-number limit are studied in a series of direct numerical simulations. The flow configuration studied consists of alternating slabs of high- and low-density fluid in a triply periodic domain. Density ratios in the range of $1.05\leqslant R\equiv \unicode[STIX]{x1D70C}_{1}/\unicode[STIX]{x1D70C}_{2}\leqslant 10$ are investigated. The flow produces temporally evolving shear layers. A perpendicular density–pressure gradient is maintained in the mean as the flow evolves, with multi-scale baroclinic torques generated in the turbulent flow that ensues. For all density ratios studied, the simulations attain Reynolds numbers at the beginning of the fully developed turbulence regime. An empirical relation for the convection velocity predicts the observed entrainment-ratio and dominant mixed-fluid composition statistics. Two mixing-layer temporal evolution regimes are identified: an initial diffusion-dominated regime with a growth rate ${\sim}t^{1/2}$ followed by a turbulence-dominated regime with a growth rate ${\sim}t^{3}$ . In the turbulent regime, composition probability density functions within the shear layers exhibit a slightly tilted (‘non-marching’) hump, corresponding to the most probable mole fraction. In conclusion, the shear layers preferentially entrain low-density fluid by volume at all density ratios, which is reflected in the mixed-fluid composition.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2025

Competing mechanisms at vibrated interfaces of density-contrast fluids

Fluid-fluid interfacial instability and subsequent fluid mixing are ubiquitous in nature and engineering. The hydrodynamic instability of fluid interfaces has long centered on the pressure gradient-driven long-wavelength Rayleigh-Taylor instability and the resonance-induced short-wavelength Faraday instability. However, neither instability alone can explain the dynamics when both mechanisms are present. We identify a previously unseen multi-modal instability emerging from their coexistence. When the denser fluid is polydimethylsiloxane, the mixed region at a high density contrast (Atwood number = 0.9) spans a vibration amplitude range approximately twice the gravitational acceleration. Using Floquet stability analysis, we show how vibrations govern transitions between the RT and Faraday instabilities, leading to contention between these instabilities rather than resonant enhancement. Here, the initial transient growth is represented by the exponential modal growth of the most unstable Floquet exponent, along with its accompanying periodic behavior. Direct numerical simulations validate these findings and track interface breakup into the multiscale and nonlinear regimes. Specifically, we show that growing RT modes nonlinearly suppresses Faraday responses even when the initial growth rate of the Faraday instability is 3.63 times that of RT, so a bidirectional competition hinders their sustained coexistence.

Direct numerical simulations↗

DOE OSTI2011

Diffusion Synthetic Acceleration for High-Order Discontinuous Finite Element SN Transport Schemes and Application to Locally Refined Unstructured Meshes

Diffusion synthetic acceleration (DSA) schemes compatible with adaptive mesh refinement (AMR) grids are derived for the SN transport equations discretized using high-order discontinuous finite elements. These schemes are directly obtained from the discretized transport equations by assuming a linear dependence in angle of the angular flux along with an exact Fick's law and, therefore, are categorized as partially consistent. These schemes are akin to the symmetric interior penalty technique applied to elliptic problems and are all based on a second-order discontinuous finite element discretization of a diffusion equation (as opposed to a mixed or P1 formulation). Therefore, they only have the scalar flux as unknowns. A Fourier analysis has been carried out to determine the convergence properties of the three proposed DSA schemes for various cell optical thicknesses and aspect ratios. Out of the three DSA schemes derived, the modified interior penalty (MIP) scheme is stable and effective for realistic problems, even with distorted elements, but loses effectiveness for some highly heterogeneous configurations. The MIP scheme is also symmetric positive definite and can be solved efficiently with a preconditioned conjugate gradient method. Its implementation in an AMR SN transport code has been performed for both source iteration and GMRes-based transport solves, with polynomial orders up to 4. Numerical results are provided and show good agreement with the Fourier analysis results. Results on AMR grids demonstrate that the cost of DSA can be kept low on locally refined meshes.

42 ENGINEERING↗

DOE OSTI2015

The influence of ions and the induced secondary emission on the nanosecond high-gradient microwave breakdown at metal surface

The mechanism of ultrafast breakdown at metal/vacuum interface in the high-power microwave waveguides is studied. In order to realize the nanosecond discharge, the required ambient gas pressure above the metal surface is approximately calculated as high as several Torr due to the low ionization-rate for high-energy electrons and short pulse. The local high pressure may come from the evaporated microscopic protrusions due to Joule heating and gas desorption. Besides, ions accelerated by the ambient space charge field could obtain sufficient high energy to collide and sputter the metal atoms to increase the ambient pressure. The positive feedbacks during the rapid discharge are studied by particle-in-cell simulation. The relatively high-energy ions could generate secondary electrons. It is shown that, as the positive feedback, the secondary electrons induce the gas desorption and stronger ionization, resulting in ion and electron density increasing as well as sheath field further increasing. As a result, more higher-energy ions bombard metal surface, leading to higher secondary electron yield and higher density plasma generated to cut off the microwave transmission finally. These nonlinear courses realize the ultrafast discharge in waveguides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Measurements of Beam Spin Asymmetries in p+p0 and p´p0 Dihadron Production at CLAS12

Semi-Inclusive Deep Inelastic Scattering (SIDIS) is a powerful experimental tool for studying the internal structure and dynamics of the proton, revealing how quarks and gluons are distributed and interact within it. SIDIS describes a process where an elec tron scatters off one of the constituent quarks within the proton, causing it to undergo hadronization, creating multiple hadrons in the final state. Through factorization, the full process can be split into probabilistic components: one which describes the internal structure of the proton using Parton Distribution Functions (PDFs), and another which describes the hadronization process using Fragmentation Functions (FFs). These functions are non-perturbative quantities of Quantum Chromodynamics (QCD), meaning they cannot be calculated directly from first principles and must instead be extracted from experimental measurements. Acommon approach for accessing PDFs and FFs using SIDIS is to measure asymmetries. In this context, asymmetries correspond to subtle differences in the angular distribution of outgoing particles that arise when the spin orientation of the incoming beam or target is reversed. Because many of these effects only appear when spin is involved, they isolate specific, nuanced properties of the proton’s spin-structure that are otherwise hidden in spin averaged measurements. In practice, they show up as specific azimuthal modulations (e.g., sin ¿R, sin(¿h ´ ¿R)), whose amplitudes isolate convolutions of PDFs and FFs at leading and subleading twist. Non-zero asymmetries of these angular distributions can be traced back to unique combinations of PDFs and FFs, offering a way to probe them directly. In this work, we measure SIDIS by analyzing high energy electron-proton scattering events using the CLAS12 detector at Jefferson Lab. This study focuses on subset of SIDIS referred to as dihadron SIDIS, where pairs of hadrons — here p+p0 and p´p0 — are observed. We analyzed these dihadrons using detector data collected during Fall 2018 and Spring 2019, where longitudinally polarized electrons from the CEBAF accelerator were incident on a liquid hydrogen target. A photon classifier using a Gradient Boosted Trees (GBTs) architecture was trained using Monte Carlo simulations to reduce the amount of iv false combinatorial background p0’s. When deployed on experimental data, the model in creases our dihadron statistics by up to five-fold compared to previous CLAS12 p0 analyses. This work reports the first measurements of beam spin asymmetries for p+p0 and p´p0 dihadron production in SIDIS. The measured asymmetries offer new insights to the spin-dependent structure and dynamics within the proton, as well as the spin-dependent properties of quark fragmentation. Non-zero twist-3 sin¿R amplitudes are observed, pro viding sensitivity to the subleading twist PDF e(x). The PDF e(x) encodes quark-gluon correlations within the proton — a property that is otherwise inaccessible at leading twist. Additionally, this work measured significant twist-2 modulations carried by sin(¿h ´ ¿R) and sin(2¿h ´2¿R), providing experimental access to the helicity dihadron fragmentation function (DiFF) GK 1 . Because there is no equivalent quark helicity-dependent FF in single pion SIDIS, the DiFF GK 1 offers a unique lens into novel spin-dependent fragmentation. For instance, the twist-2 modulations observed in this study are enhanced by vector mesons created during fragmentation — a behavior predicted by phenomenological models. This study broadens our understanding of dihadron fragmentation, revealing new details about the flavor and charge dependence of hadronization.

Matousek, Gregory [Duke Univ., Durham, NC (United ↗

NASA NTRS2026

AC and DC Fault Management for Megawatt Electrified Aircraft Electrical Powertrains Task 3: Lifetime and Reliability of Electrical Insulators

This research project was a collaborative investigation between researchers at the RTX Technology Research Center (RTRC) and the University of Texas at Austin and made a significant contribution to enabling electric aircraft. The transport of electric power between the points of generation and use requires power cables. These cables must be smaller, lighter and provide a more predictable life than power cables used in stationary applications. Consequently, this investigation provided heretofore unavailable information supporting the safety and reliability of smaller lighter power cables for electrified aircraft. In addition, the research identified key additional engineering data needed to support quantitative reliability assessments. Important advances included: • Demonstrated that at least one manufacturer can make a novel, smaller, lighter power cable that is free from serious defects. • Developed and published an appropriate analytical construct to describe the life of this novel cable. This is a necessary step for use in aviation where the understanding of remaining life is critical. • Demonstrated thermal-mechanical aging that suggested 1000+ flights before the thermal-mechanical processes produced defects large enough that the defect growth was accelerated electrically. • Showed that electrical aging took place at two rates. The first possibly lasting weeks to months and the second possibly days to weeks. If robust, this provides a good diagnostic for cable replacement. • Demonstrated that the traditional electrical testing of cable materials using manufactured voids can be misleading due to the size of the voids. Emerging laser drilling technology permitted demonstration that the physics of failure in realistically small voids is different from that in the unrealistically large voids used in earlier research, which is very important for high-quality, high-performance, small aircraft cables. Although this project represents a significant contribution to the specifics of cable aging in the aircraft environment, important additional research remains to be completed, including: • Non-uniform thermal cycling by applying the heat from the center conductor to maximize thermal stress next to the core area where the electric gradient is the strongest. This builds on the uniform thermal cycling that has been completed. • The augmentation of the thermal-mechanical failure rate by electrical processes. Better understanding of these time constants strongly affects the ability to predict life. • Termination design: Terminations provide not only electrical reflection potential, but a location for a series arc fault and an area where ozone can diffuse into the center conductor and negatively affect cable insulation. • The abrasion and ozone resistance of the cable jacket. • Pressure cycling as an accelerant of thermal, mechanical, and/or electrical aging. • Possible methods for online PD detection and offline PD localization

model↗

DOE OSTI2015

Knowledge-based prediction of plan quality metrics in intracranial stereotactic radiosurgery

Purpose: The objective of this work was to develop a comprehensive knowledge-based methodology for predicting achievable dose–volume histograms (DVHs) and highly precise DVH-based quality metrics (QMs) in stereotactic radiosurgery/radiotherapy (SRS/SRT) plans. Accurate QM estimation can identify suboptimal treatment plans and provide target optimization objectives to standardize and improve treatment planning. Methods: Correlating observed dose as it relates to the geometric relationship of organs-at-risk (OARs) to planning target volumes (PTVs) yields mathematical models to predict achievable DVHs. In SRS, DVH-based QMs such as brain V{sub 10Gy} (volume receiving 10 Gy or more), gradient measure (GM), and conformity index (CI) are used to evaluate plan quality. This study encompasses 223 linear accelerator-based SRS/SRT treatment plans (SRS plans) using volumetric-modulated arc therapy (VMAT), representing 95% of the institution’s VMAT radiosurgery load from the past four and a half years. Unfiltered models that use all available plans for the model training were built for each category with a stratification scheme based on target and OAR characteristics determined emergently through initial modeling process. Model predictive accuracy is measured by the mean and standard deviation of the difference between clinical and predicted QMs, δQM = QM{sub clin} − QM{sub pred}, and a coefficient of determination, R{sup 2}. For categories with a large number of plans, refined models are constructed by automatic elimination of suspected suboptimal plans from the training set. Using the refined model as a presumed achievable standard, potentially suboptimal plans are identified. Predictions of QM improvement are validated via standardized replanning of 20 suspected suboptimal plans based on dosimetric predictions. The significance of the QM improvement is evaluated using the Wilcoxon signed rank test. Results: The most accurate predictions are obtained when plans are stratified based on proximity to OARs and their PTV volume sizes. Volumes are categorized into small (V{sub PTV} < 2 cm{sup 3}), medium (2 cm{sup 3} < V{sub PTV} < 25 cm{sup 3}), and large (25 cm{sup 3} < V{sub PTV}). The unfiltered models demonstrate the ability to predict GMs to ∼1 mm and fractional brain V{sub 10Gy} to ∼25% for plans with large V{sub PTV} and critical OAR involvements. Increased accuracy and precision of QM predictions are obtained when high quality plans are selected for the model training. For the small and medium V{sub PTV} plans without critical OAR involvement, predictive ability was evaluated using the refined model. For training plans, the model predicted GM to an accuracy of 0.2 ± 0.3 mm and fractional brain V{sub 10Gy} to 0.04 ± 0.12, suggesting highly accurate predictive ability. For excluded plans, the average δGM was 1.1 mm and fractional brain V{sub 10Gy} was 0.20. These δQM are significantly greater than those of the model training plans (p < 0.001). For CI, predictions are close to clinical values and no significant difference was observed between the training and excluded plans (p = 0.19). Twenty outliers with δGM > 1.35 mm were identified as potentially suboptimal, and replanning these cases using predicted target objectives demonstrates significant improvements on QMs: on average, 1.1 mm reduction in GM (p < 0.001) and 23% reduction in brain V{sub 10Gy} (p < 0.001). After replanning, the difference of δGM distribution between the 20 replans and the refined model training plans was marginal. Conclusions: The results demonstrate the ability to predict SRS QMs precisely and to identify suboptimal plans. Furthermore, the knowledge-based DVH predictions were directly used as target optimization objectives and allowed a standardized planning process that bettered the clinically approved plans. Full clinical application of this methodology can improve consistency of SRS plan quality in a wide range of PTV volume and proximity to OARs and facilitate automated treatment planning for this critical treatment site.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2010

Detection of concealed and buried chemicals by using multifrequency excitations

In this paper, we present a new type of concealed and buried chemical detection system by stimulating and enhancing spectroscopic signatures with multifrequency excitations, which includes a low frequency gradient dc electric field, a high frequency microwave field, and higher frequency infrared (IR) radiations. Each excitation frequency plays a unique role. The microwave, which can penetrate into the underground and/or pass through the dielectric covers with low attenuation, could effectively transform its energy into the concealed and buried chemicals and increases its evaporation rate from the sample source. Subsequently, a gradient dc electric field, generated by a Van De Graaff generator, not only serves as a vapor accelerator for efficiently expediting the transportation process of the vapor release from the concealed and buried chemicals but also acts as a vapor concentrator for increasing the chemical concentrations in the detection area, which enables the trace level chemical detection. Finally, the stimulated and enhanced vapors on the surface are detected by the IR spectroscopic fingerprints. Our theoretical and experimental results demonstrate that more than sixfold increase in detection signal can be achieved by using this proposed technology. The proposed technology can also be used for standoff detection of concealed and buried chemicals by adding the remote IR and/or thermal spectroscopic and imaging detection systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Omnigenous stellarators with improved ideal and kinetic ballooning stability

Omnigenity is a property of a magnetic field which ensures confinement of trapped particles. It is a necessary requirement for any high-performance stellarator. After creating an omnigenous equilibrium, one must also ensure reduced transport resulting from kinetic and magnetohydrodynamic (MHD) instabilities. To this end, we leverage the GPU-accelerated DESC optimization suite, which is used to design stable, finite-β omnigenous equilibria with poloidal, toroidal, and helical symmetry, achieving Mercier, ideal ballooning, and as a consequence, improved kinetic ballooning stability. We discover stellarators with second stability, a regime of large pressure gradient where an equilibrium becomes ideal ballooning stable, and demonstrate and explore both using theory and gyrokinetic simulations the connection between ideal and kinetic ballooning stability.

optimization↗

DOE OSTI2021

Evolution of the superconducting properties from binary to ternary APC-Nb 3 Sn wires

We present a study conducted on binary Tube Type and ternary powder-in-tube Nb 3 Sn wires manufactured using the artificial pinning centres-internal oxidation method. All the specimens are doped with Zr: oxide nano-particles of this element are responsible for the pinning improvement, both by refining the A-15 grain-size and their own point-pinning contribution. Low-field J c magnetometry confirms that the hadron-hadron Future Circular Collider (FCC-hh) specifications are met by one ternary doped-sample. The differences in microstructure were assessed by scanning electron microscopy/transmission electron microscopy to clarify the reasons for the pinning improvement between the two generations. The deviations from the Dew Hughes model are also discussed, underlying some non-linear addition due to competition between the two pinning mechanisms. Finally, we show how the introduction of Ta as a ternary addition influences the A-15 phase by focusing on the radial inhomogeneities, evaluating the T c distribution and Sn composition gradients. The latter are used to model the currents, enabling us to evaluate the individual weights of the pinning mechanisms and their absolute contributions at the High Luminosity-Large Hadron Collider and FCC-hh dipoles operational points.

43 PARTICLE ACCELERATORS↗

DOE OSTI2023

Flux Expulsion Studies of Niobium Material of 650 MHz Cavities for PIP-II

Two different vendors supplied the niobium sheet material for PIP-II 5-cell 650 MHz cavities, which was characterized by multiple different ASTM sizes. Cavities subsequently fabricated from these sheets were heat-treated at various temperatures, then the cavities’ flux-expulsion performance was measured. Where the initial measurements of vendor O materials showed that nearly all flux remained trapped despite a high thermal gradient, 900C heat treatment subsequently improved the flux expulsion to an acceptable rate. Understanding and characterizing vendor O materials in this way is key for upcoming and future projects planning to employ niobium sheet from this supplier.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Experience of micromultileaf collimator linear accelerator based single fraction stereotactic radiosurgery: Tumor dose inhomogeneity, conformity, and dose fall off

Purpose: Sharp dose fall off outside a tumor is essential for high dose single fraction stereotactic radiosurgery (SRS) plans. This study explores the relationship among tumor dose inhomogeneity, conformity, and dose fall off in normal tissues for micromultileaf collimator (mMLC) linear accelerator (LINAC) based cranial SRS plans. Methods: Between January 2007 and July 2009, 65 patients with single cranial lesions were treated with LINAC-based SRS. Among them, tumors had maximum diameters {<=}20 mm: 31; between 20 and 30 mm: 21; and >30 mm: 13. All patients were treated with 6 MV photons on a Trilogy linear accelerator (Varian Medical Systems, Palo Alto, CA) with a tertiary m3 high-resolution mMLC (Brainlab, Feldkirchen, Germany), using either noncoplanar conformal fixed fields or dynamic conformal arcs. The authors also created retrospective study plans with identical beam arrangement as the treated plan but with different tumor dose inhomogeneity by varying the beam margins around the planning target volume (PTV). All retrospective study plans were normalized so that the minimum PTV dose was the prescription dose (PD). Isocenter dose, mean PTV dose, RTOG conformity index (CI), RTOG homogeneity index (HI), dose gradient index R{sub 50}-R{sub 100} (defined as the difference between equivalent sphere radius of 50% isodose volume and prescription isodose volume), and normal tissue volume (as a ratio to PTV volume) receiving 50% prescription dose (NTV{sub 50}) were calculated. Results: HI was inversely related to the beam margins around the PTV. CI had a ''V'' shaped relationship with HI, reaching a minimum when HI was approximately 1.3. Isocenter dose and mean PTV dose (as percentage of PD) increased linearly with HI. R{sub 50}-R{sub 100} and NTV{sub 50} initially declined with HI and then reached a plateau when HI was approximately 1.3. These trends also held when tumors were grouped according to their maximum diameters. The smallest tumor group (maximum diameters {<=}20 mm) had the most HI dependence for dose fall off. For treated plans, CI averaged 2.55{+-}0.79 with HI 1.23{+-}0.06; the average R{sub 50}-R{sub 100} was 0.41{+-}0.08, 0.55{+-}0.10, and 0.65{+-}0.09 cm, respectively, for tumors {<=}20 mm, between 20 and 30 mm, and >30 mm. Conclusions: Tumor dose inhomogeneity can be used as an important and convenient parameter to evaluate mMLC LINAC-based SRS plans. Sharp dose fall off in the normal tissue is achieved with sufficiently high tumor dose inhomogeneity. By adjusting beam margins, a homogeneity index of approximately 1.3 would provide best conformity for the authors' SRS system.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2018

High power experimental studies of hybrid photonic band gap accelerator structures

This paper reports the first high power tests of hybrid Photonic Band Gap (PBG) accelerator structures. Three hybrid PBG (HPBG) structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM02 mode, with suppression of both lower order modes, such as the TM11 mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion of the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19 MV/m, corresponding to a surface electric field of 78 MV/m, with a breakdown probability of 0.5 per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20 MV/m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. This research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

Segmentation and Classification of Fission as Pores in Reactor Irradiated Annular U–10Zr Metallic Fuel Using Machine Learning Models

Metallic fuels, particularly U—10Zr, are promising candidates for next-generation sodium-cooled fast reactors. Irradiation of nuclear fuels in reactors can lead to the formation of solid and gas fission product which subsequently forms microstructural pores, deteriorating fuel performance. Due to the massive amount of pores and complex phases formed, a quantitative description of fission gas pores is not yet available, preventing the development of microstructure-informed fuel performance modeling for fuel qualification. This paper applied a pre-trained deep learning model to ~10,260 high magnification scanning electron microscopy images. This method increased the accuracy of fission gas pore segmentation and allows statistical features to be extracted which cannot be achieved manually. A pre-trained decision tree model worked on the segemenation results and further classified the pores into different categories to produce a correlation between the pores, movement of lanthanides, and temperature gradient during irradiation. Finally, this paper emphasizes the potentials of machine learning models to accelerate fuel research, development, and qualification for advanced reactors.

36 MATERIALS SCIENCE↗