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Self-driven ion deflectometry measurements using MeV fusion-driven protons and accelerated deuterons in the deuterated hybrid x-pinch on the MAIZE LTD generator
Abstract We report on the results of point-projection ion deflectometry measurements from a mid-size university z-pinch experiment. A 1 MA 8 kJ LTD generator at the University of Michigan (called MAIZE) drove a hybrid x-pinch (HXP) with a deuterated polyethylene fiber load to produce a point-like source of MeV ions for backlighting. In these experiments, 2.7 MeV protons were generated by DD beam-target fusion reactions. Due to the kinematics of beam-target fusion, the proton energies were down-shifted from the more standard 3.02 MeV proton energy that is released from the center-of-mass rest frame of a DD reaction. In addition to the 2.7 MeV protons, strongly anisotropic beams of 3 MeV accelerated deuterons were detected by ion diagnostics placed at a radial distance of 90 mm from the x-pinch. Numerical reconstruction of experimental data generated by deflected hydrogen ion trajectories evaluated the total current in the vacuum load region. Numerical ion-tracking simulations show that accelerated deuteron beams exited the ion source region at large angles with respect to the pinch current direction.
A multi-beamlet analysis of the MITICA accelerator
The thermo-mechanical analysis and the mechanical design of the accelerator of MITICA (i.e. the full size prototype of the ITER neutral beam injector under construction at RFX [1]) are based on the calculation of the power deposition induced by particle impacts. This calculation is performed by EAMCC [2], a relativistic particle tracking code based on the Monte-Carlo method for describing collisions inside the accelerator, under prescribed electric and magnetic fields. The magnetic field maps are produced by 3D codes, while the electric field maps come from the 2D axi-symmetric code SLACCAD [3]. In order to perform a multi-beamlet analysis, which allows to take into account the beamlet-beamlet repulsion, and to consider other effects neglected under the hypothesis of axi-symmetric beam, a fully 3D version of the code is required. In this paper, a modified version of EAMCC, fully 3D, capable of modifying the mesh of the 3D maps and of dealing with uneven meshes is presented. A finer mesh is used just in the regions where a more detailed description of the fields is required, for a more realistic simulation. A comparison between the original code and the modified version is presented at first, as a validation of the modifications introduced in the latter. Subsequently, the main results of a single-beamlet analysis performed with the two versions of the code are shown and the differences between the 2D and the 3D simulations discussed. The last part is dedicated to the multi-beamlet simulation of the accelerator.
Bottom-up design of actinide materials from molecular clusters: Demonstration of a general-purpose simulation capability leveraging machine-learned atomic potentials
Actinide thin-film coatings such as uranium dioxide (UO 2 ) play an important role in nuclear reactors and other mission-relevant applications, but realization of their potential requires a deep fundamental understanding of the chemical vapor deposition (CVD) processes used for their growth. The slow experimental progress can be attributed, in part, to the standard safety guidelines associated with handling uranium byproducts, which are often corrosive, toxic, and radioactive. Accurate simulation techniques, when used in concert with experiment, can improve laboratory safety, material durability, and deliverable timeframes. However, state-of-the-art computational methods are either insufficiently accurate or intractably expensive. To remedy this situation, in this project we suggested a machine-learning (ML) accelerated workflow for simulating molecular clustering toward deposition. As a benchmark test case, we considered molecular clustering in steam and assessed independent components of our workflow by comparing with measured thermodynamic properties of water. After analyzing each component individually and finding no fundamental barrier to realization of the workflow, we attempted to integrate the ML component, a Sandia-developed tool called FitSNAP. As this was the first application of FitSNAP to atoms and molecules in the gas phase at Sandia, the method required more fitting data than was originally anticipated. Systematic improvements were made by including in the fit data diatomic potentials, molecular single-bond-breaking curves, and symmetry-constrained intermolecular potentials. We concluded that our strategy provides a feasible pathway toward modeling CVD and related processes, but that extensive training data must be generated before it can be of practical use.
Λ CDM is Consistent with SPARC Radial Acceleration Relation
Recent analysis of the Spitzer Photometry and Accurate Rotation Curve (SPARC) galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves and the acceleration due to the baryonic components of the disk. It has been suggested that this relation may be evidence for new physics, beyond Λ CDM . In this Letter, we show that 32 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star-forming, rotationally supported disks were simulated with a WMAP3 Λ CDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration relation is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.
Radiation Testing at Sandia National Laboratories: Sandia – JPL Collaboration for Europa Lander
Sandia National Laboratories (SNL) is assisting Jet Propulsion Laboratory in undertaking feasibility studies and performance assessments for the Planetary Protection aspect of the Europa Lander mission. The specific areas of interest for this project are described by task number. This white paper presents the evaluation results for Task 2, Radiation Testing, which was stated as follows: Survey SNL facilities and capabilities for simulating the Europan radiation environment and assess suitability for: A. Testing batteries, electronics, and other component and subsystems B. Exposing biological organisms to assess their survivability metrics. The radiation environment the Europa Lander will encounter on route and in orbit upon arrival at its destination consists primarily of charged particles, energetic protons and electrons with the energies up to 1 GeV. The charged particle environments can be simulated using the accelerators at the Ion Beam Laboratory. The Gamma Irradiation Facility and its annex, the Low Dose Rate Irradiation Facility, offer irradiations using Co-60 gamma sources (1.17 and 1.33 MeV), as well as Cs-137 gamma (0.661 MeV) AmBe neutron (0-10 MeV) sources.
Laser-ion acceleration using mixed compositions: Tailoring the target for each species
Particle-in-cell simulations of laser- ion acceleration demonstrate marked discrepancies in the acceleration experienced by the different ion species in complex target compositions, especially when the target becomes relativistically transparent to the pulse during irradiation. Beginning with proton contaminants in a carbon target, we show how the higher charge-to-mass ratio of the protons results in species stratification and late-time suppression of the carbon acceleration. The target normal sheath acceleration (TNSA) primarily experienced by the protons can be exploited to mitigate this tamping by using a shaped rear surface of the target, leaving the break-out afterburner-driven carbons to accelerate close to the laser axis and then experience less tamping during a late-time TNSA phase. Here, we then explore preferentially accelerating the lighter species in a mixed composition target, particularly focusing on deuteron beam applications. We examine three different target compositions with the same areal electron density, CD 2 , CH 2 , and 7 LiD, and propose an alternative shaping of the rear surface of 7 LiD to increase the number of high-energy deuterons in the beam.
Energy conserving quadrature based dimensionality reduction for nonlinear hydrodynamics problems
Projection based dimensionality reduction is used to approximate the full discretiza tion of a PDE problem in order to reduce the cost of its numerical simulation while staying faithful to the full dynamics. For nonlinear problems, hyperreduction methods are additionally needed to remove the dependence of the nonlinear terms on the full problem’s size. In this project, we develop an energy conserving hyperreduction method and apply it to Eulerian-Lagrangian hydrodynamics problems, demonstrating that the reduced model successfully accelerates the numerical simulations while conserving the problem’s total energy with high accuracy.
Machine-Learning Assisted Identification of Battery Life Models
Predictive battery life models are commonly utilized to extrapolate degradation trends observed during accelerated aging tests for simulation of degradation in real-world applications. Thus, fitting accelerated aging data as accurately as possible and with low uncertainty is crucial for making believable projections of battery lifetime, but it is challenging to identify algebraic expressions that accurately fit multivariate degradation trends. A review of models published in literature reveal some common expressions for fitting calendar aging data, which is only dependent on temperature and state-of-charge, but no consistency across many models for fitting cycle aging data, indicating the need for a statistically rigorous data driven approach for developing empirical models. This talk will describe a machine-learning assisted method for identification of predictive battery life models utilizing bilevel optimization and symbolic regression. Bilevel optimization with cross-validation is used to statistically determine cell- and stress-dependent model parameters, while symbolic regression identifies both linear and multiplicative candidate expressions to predict stress-dependent degradation rates by selecting low-order subsets of features from a generated feature library. Because model expressions are identified empirically, it is crucial to ensure resulting models behave according to physical expectations, so the stability of models for interpolation or extrapolation is interrogated qualitatively through simulation and quantitatively through cross-validation and uncertainty quantification via bootstrap resampling. This model identification approach substantially improves upon models identified purely using expert judgement in terms of both accuracy and uncertainty. Model simulation and validation is then conducted by deriving a state-equation form of the predictive model, enabling simulation of battery aging under dynamic stresses. This enables validation of the predictive battery model on lab-based tests with varying conditions or on drive-cycle or application-cycle testing protocols. Parameter uncertainty can be carried forward into model simulation, giving lifetime estimates and confidence windows for cell- or system-level lifetime. The financial impact of battery model uncertainty can be estimated by incorporating uncertainty into a technoeconomic model.
Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7−3946
We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7−3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H i emission. We present a series of simulated images of RX J1713.7−3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton , whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H i observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.
Electron acceleration by parallel and perpendicular electric fields during magnetic reconnection without guide field
In this work, electron acceleration due to the electric field parallel to the background magnetic field during magnetic reconnection with no guide field is investigated by theory and two-dimensional electromagnetic particle-in-cell simulations and compared with acceleration due to the electric field perpendicular to the magnetic field. The magnitude of the parallel electric potential shows dependence on the ratio of the plasma frequency to the electron cyclotron frequency as (ω pe /Ω e ) -2 and on the background plasma density as N$^{-½}_{b}$ . In the Earth's magnetotail, the parameter ω pe /Ω e ~9 and the background (lobe) density can be of the order of 0.01 cm -3 , and it is expected that the parallel electric potential is not large enough to accelerate electrons up to 100 keV. Therefore, we must consider the effect of the perpendicular electric field to account for electron energization in excess of 100 keV in the Earth's magnetotail. Trajectories for high-energy electrons are traced in a simulation to demonstrate that acceleration due to the perpendicular electric field in the diffusion region is the dominant acceleration mechanism, rather than acceleration due to the parallel electric fields in the exhaust regions. For energetic electrons accelerated near the X line due to the perpendicular electric field, pitch angle scattering converts the perpendicular momentum to the parallel momentum. On the other hand, for passing electrons that are mainly accelerated by the parallel electric field, pitch angle scattering converting the parallel momentum to the perpendicular momentum occurs. In this way, particle acceleration and pitch angle scattering will generate heated electrons in the exhaust regions.
Beam dynamics simulations of post low energy beam transport section in RAON heavy ion accelerator
RAON (Rare isotope Accelerator Of Newness) heavy ion accelerator of the rare isotope science project in Daejeon, Korea, has been designed to accelerate multiple-charge-state beams to be used for various science programs. In the RAON accelerator, the rare isotope beams which are generated by an isotope separation on-line system with a wide range of nuclei and charges will be transported through the post Low Energy Beam Transport (LEBT) section to the Radio Frequency Quadrupole (RFQ). In order to transport many kinds of rare isotope beams stably to the RFQ, the post LEBT should be devised to satisfy the requirement of the RFQ at the end of post LEBT, simultaneously with the twiss parameters small. We will present the recent lattice design of the post LEBT in the RAON accelerator and the results of the beam dynamics simulations from it. In addition, the error analysis and correction in the post LEBT will be also described.
Polymer dynamics under cylindrical confinement featuring a locally repulsive surface: A quasielastic neutron scattering study
We investigated the effect of intermediate cylindrical confinement with locally repulsive walls on the segmental and entanglement dynamics of a polymer melt by quasielastic neutron scattering. As a reference, we measured the corresponding polymer melt under identical conditions. The locally repulsive confinement was realized by hydrophilic anodic alumina nanopores with a diameter of 20 nm. The end-to-end distance of the hydrophobic infiltrated polyethylene-alt-propylene was close to this diameter. In the case of hard wall repulsion with negligible local attraction, several simulations predicted an acceleration of segmental dynamics close to the wall. Other than in attractive or neutral systems, where the segmental dynamics is slowed down, we found that the segmental dynamics in the nanopores is identical to the local mobility in the bulk. Even under very careful scrutiny, we could not find any acceleration of the surface-near segmental motion. On the larger time scale, the neutron spin-echo experiment showed that the Rouse relaxation was not altered by confinement effects. Moreover, the entanglement dynamics was not affected. Thus at moderate confinement conditions, facilitated by locally repulsive walls, the dynamics remains as in the bulk melt, a result that is not so clear from simulations.
Developments in SRW Code and Sirepo Framework Supporting Simulation of Time-Dependent Coherent X-ray Scattering Experiments
Physical optics simulations for beamlines and experiments are essential for the effective use of synchrotron light source facilities such as NSLS-II at BNL. The SRW software package supports such source-to-detector simulations for coherent X-ray scattering and imaging experiments through its Python interface and Sirepo browser-based graphical user interface. This allows one to define custom sample models, assess the feasibility of an experiment, and estimate most appropriate beamline settings before using valuable beamtime. We discuss the recent use of general-purpose GPU resources and coherent mode decomposition algorithms in SRW to accelerate physical optics simulations with partially coherent X-rays. To illustrate these new capabilities, we describe simulations of typical time series of partially coherent scattering images used in X-ray Photon Correlation Spectroscopy (XPCS) experiments; aiming to characterize the nanoscale dynamics of a disordered sample, representing a solution of nanoparticles undergoing Brownian diffusion.
Maximum Energy of Particles Accelerated in Gamma-Ray Burst Afterglow Shocks
Particle acceleration in relativistic collisionless shocks remains an open problem in high-energy astrophysics. Particle-in-cell (PIC) simulations predict that electron acceleration in weakly magnetized shocks proceeds via small-angle scattering, leading to a maximum electron energy significantly below the Bohm limit. This upper bound on electron energy manifests observationally as a characteristic synchrotron cutoff, providing a direct probe of the underlying acceleration physics. Gamma-ray burst (GRB) afterglows offer an exceptional laboratory for testing these predictions. Here, we model the spectral evolution of GRB afterglows during the relativistic deceleration phase, incorporating PIC-motivated acceleration prescriptions and self-consistently computing synchrotron and synchrotron self-Compton emission. We find that low-energy bursts in low-density environments, typical of short GRBs, exhibit a pronounced synchrotron cutoff in the GeV band within minutes to hours after the trigger. Applying our framework to GRB 190114C and GRB 130427A, we find that current observations are insufficient to discriminate between PIC-motivated acceleration and the Bohm limit, primarily due to poor photon statistics in the Fermi-Large Area Telescope band. Nevertheless, future MeV–TeV afterglow observations can break model degeneracies and place substantially tighter constraints on the mechanisms responsible for particle acceleration in relativistic shocks. To this end, we simulate a fiducial nearby short GRB as a promising probe of the cutoff location, for which the two acceleration scenarios are cleanly distinguishable and the detection of such an event in the near future remains feasible.
Favorable target positions for intense laser acceleration of electrons in hydrogen-like, highly-charged ions
Classical relativistic Monte Carlo simulations of petawatt laser acceleration of electrons bound initially in hydrogen-like, highly-charged ions show that both the angles and energies of the laser-accelerated electrons depend on the initial ion positions with respect to the laser focus. Electrons bound in ions located after the laser focus generally acquire higher (≈GeV) energies and are ejected at smaller angles with respect to the laser beam. Our simulations assume a tightly-focused linearly-polarized laser pulse with intensity approaching 10{sup 22 }W/cm{sup 2}. Up to fifth order corrections to the paraxial approximation of the laser field in the focal region are taken into account. In addition to the laser intensity, the Rayleigh length in the focal region is shown to play a significant role in maximizing the final energy of the accelerated electrons. Results are presented for both Ne{sup 9+} and Ar{sup 17+} target ions.
Expected Dose Rates from 1 MeV Electron Accelerator
The purpose of this study was to simulate UCLA’s 1 MeV electron accelerator and calculate the expected dose rates at various locations inside of the lab and outside of the building to see if they fall into safe levels.
Properties and parameters of the electron beam injected into the mirror magnetic trap of a plasma accelerator
The parameters of the injector of an axial plasma beam injected into a plasma accelerator operating on the basis of gyroresonance acceleration of electrons in the reverse magnetic field are determined. The trapping of the beam electrons into the regime of gyroresonance acceleration is numerically simulated by the particle- in-cell method. The optimal time of axial injection of the beam into a magnetic mirror trap is determined. The beam parameters satisfying the condition of efficient particle trapping into the gyromagnetic autoresonance regime are found.