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NASA NTRS1994

Exact dynamic responses of periodic multi-span beams under convected pressure fields

Response of a structure to a convected pressure field generated by far-field jet-noise or turbulent boundary layer is often of interest in engineering. The structure considered in present study is a periodic beam with equally rotational elastic supports. The convected pressure field is characterized by a broad frequency spectrum and a particular convection velocity. In the first order approximation, all the frequency components in the pressure spectrum are convected with the same velocity. In this paper, both finitely and infinitely long periodic beams under convected harmonic pressure are investigated. The exact harmonic responses are obtained by introducing new expressions of mode shapes for these two types of beams into the normal mode approach. Thus, both locations and values of the response peaks in the propagation bands can be precisely predicted and the important coincidence phenomenon can be investigated in exact terms. This work provides a foundation on which the study on vibration control of structure can be conducted.

Zhu, Li-Ping↗

NASA NTRS1993

Exact element modal analysis of beam/oscillator systems

Exact modal analysis of a beam/many-oscillator system is presented. Each oscillator consists of a discrete mass having rotational inertia, and two locally-dependent springs: one being rotational and the other, translational. A constant longitudinal force is applied to the mass, and its effect is coupled with the dynamic modes. The beam's distributed mass and other material properties, and its geometric properties, do not vary within spans bounded by the oscillators, but may vary from span to span. The classical separation-of-variables technique is used to obtain a dosedform description of the dynamic matrix, and the modal frequencies are determined as the zeros of this determinant.

Broome, Taft H., Jr.↗

DOE OSTI2015

An Alternative High Luminosity LHC with Flat Optics and Long-Range Beam-Beam Compensation

In the baseline scenario of the High-Luminosity LHC (HL-LHC), the geometric loss of luminosity in the two high luminosity experiments due to collisions with a large crossing angle is recovered by tilting the bunches in the interaction region with the use of crab cavities. A possible backup scenario would rely on a reduced crossing angle together with flat optics (with different horizontal and vertical $\beta^{\ast}$values) for the preservation of luminosity performance. However, the reduction of crossing angle coupled with the flat optics significantly enhances the strength of long-range beam-beam interactions. This paper discusses the possibility to mitigate the long-range beam-beam effects by current bearing wire compensators (or e-lens). We develop a new HL-LHC parameter list and analyze it in terms of integrated luminosity performance as compared to the baseline. Further, we evaluate the operational scenarios using numerical simulations of single-particle dynamics with beam-beam effects.

Fartoukh, Stephane↗

DOE OSTI2021

Electron-Beam-Induced Molecular Plasmon Excitation and Energy Transfer in Silver Molecular Nanowires

In this work, we investigate (1) electron-beam-induced plasmon absorption spectra of Ag molecular nanowire dimers and (2) electron-beam-induced energy transfer between two nanowires. We employ linear-response time-dependent density functional theory (TDDFT) and real-time TDDFT methods to simulate the electron-beam-induced plasmonic excitations, dynamics, and corresponding electron energy loss spectrum for small models of a single molecular nanowire with four Ag atoms and for two Ag nanowires. An array of different relative orientations of nanowires and of different initial excitation conditions resulting from applying an electron beam at different positions with respect to the Ag nanowires is investigated. The results demonstrate (1) an electron beam can induce plasmonic excitations from the molecular Ag nanowire ground state to the excited states that are both optically allowed and forbidden, (2) a tunability for selective excitations that can be controlled by the position of a focused electron beam, and (3) kinetic and dynamic behaviors of time-dependent electron-beam-induced energy transfer between two Ag molecular nanowires depend on the position of the beam source and nanowire separation distance, providing insights into the spatial dependences of plasmonic couplings in nanowire arrays.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Revisiting an airgap split-optics mitigation for beam filamentation in high power lasers

We extend the split-optic approach for mitigating filamentation in a thick optical component previously proposed for small beams to conditions relevant to high-power lasers. The split-optic approach divides a thick optic into two thinner optics separated by an airgap to reduce filamentation through diffraction management. Our numerical study focuses on filamentation of a flat-top beam with intensity modulation noise sources passing through a split-optic system. The improvement in the distance to collapse in glass is shown to be potentially substantial (>30%), yet has limited increase with the airgap size, unlike the common understanding when considering a collapse of a whole beam or a sole perturbation on a beam. The improvement in the collapse distance in glass asymptotes to an upper bound value that depends mainly on the beam mean intensity and its contrast for any airgap size above some value that depends mainly on the shortest spatial periods comprising the excitation noise source. Examining the difference in the simulation results for a periodic versus a randomly generated perturbation source-term suggests that the observed effect is governed by the statistical interference dynamics of the beam while propagating through the airgap

47 OTHER INSTRUMENTATION↗

DOE OSTI2017

The development, testing and characterisation of a straw tracking detector and readout system for the Fermilab muon g-2 experiment

The anomalous magnetic moments of leptons can be both measured and theoretically predicted with high precision, and as such provide stringent tests of the Standard Model (SM) of particle physics. The anomalous magnetic moment of the muon, $a_\mu$, in particular offers sensitivity to new physics within the reach of current experiments. The current world’s best measurement of aμ made at the Brookhaven National Laboratory (BNL) deviates from the SM prediction by over 3σ, providing a tantalising but inconclusive hint that contributions from new physics may be present. A new $a_\mu$ experiment is currently under construction at the Fermi National Accelerator Laboratory (Fermilab), known as the Fermilab muon g-2 experiment. Due to commence in 2017, this new experiment is expected to improve the experimental measurement precision of $a_\mu$ by a factor of 4, and is seeking to confirm or reject the current discrepancy. The experiment, like its BNL predecessor, will measure the precession of the $\mu^{+}$ spin in a magnetic storage-ring. This new experiment has three straw tracking detectors used to measure the beam profile of the stored $\mu^{+}$, as well as other dynamic properties of the beam. This thesis describes the design of these detectors, and the data acquisition system and subsequent data processing systems that have been developed to read them out and make their data available for physics analysis. The performance of the straw trackers and the readout systems at a number of beam tests and test stands is presented, in addition to Monte-Carlo simulations of the trackers in the final experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Enhanced beam-beam modeling to include longitudinal variation during weak-strong simulation

Beam-beam interactions pose substantial challenges in the design and operation of circular colliders, significantly affecting their performance. In particular, the weak-strong simulation approach is pivotal for investigating single-particle dynamics during the collider design phase. This paper evaluates the limitations of existing models in weak-strong simulations, noting that while they accurately account for energy changes due to slingshot effects, they fail to incorporate longitudinal coordinate changes ( z variation). To address this gap, we introduce two novel transformations that enhance Hirata’s original framework by including both z variation and slingshot effect-induced energy changes. Through rigorous mathematical analysis and extensive weak-strong simulation studies, we validate the efficacy of these enhancements in achieving a more precise simulation of beam-beam interactions. Our results reveal that although z variation constitutes a higher-order effect and does not substantially affect the emittance growth rate within the specific design parameters of the Electron-Ion Collider, the refined model offers improved accuracy, particularly in scenarios involving the interaction between beam-beam effects and other random diffusion processes, as well as in simulations incorporating realistic lattice models. Published by the American Physical Society 2024

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2025

Advanced Modeling of Beam Physics and Performance Optimization for Nuclear Physics Colliders

High energy colliders provide a critical tool in nuclear physics study by probing the fundamental structure and dynamics of matter. To maximize the potential of scientific discovery in nuclear physics study, it is important to optimize the parameters of these colliders to attain the best performance. The performance of a collider is typically measured by its integrated luminosity of colliding beams since the probability of a new event is proportional to the integrated luminosity. However, the achievable luminosity is limited by the electromagnetic interactions (beam-beam effects) of two colliding beams at higher energy, and the interplay between the space-charge effects and the beam-beam effects at lower energy. To achieve the best performance of a collider means to attain the highest luminosity of the collider with optimized collider parameters. Optimizing the collider’s machine parameters is both computationally and experimentally expensive. A fast and robust computational framework including beam-beam and space-charge effects will be critical to attaining the best performance of the collider. In this project, we will study the beam dynamics challenges, specifically the interplay of the space-charge and the beam-beam effects, and the machine tuning models for maximizing the performance of RHIC experiments. We will develop an advanced modeling framework based on first-principles physical simulations, lattice models and the state-of-the-art machine learning methods and apply this framework to performance improvement of the RHIC in operation. We will build data manipulation packages to connect the simulation data and the experimental data with the framework, develop a self-consistent hybrid model of space-charge and beam-beam effects, study underlying physics mechanisms, build surrogate models using the labeled data, integrate the models into the advanced modeling framework, and apply the framework to RHIC luminosity (STAR and sPHENIX) optimization. The success of this project would substantially improve the performance of existing and future colliders and increase the opportunity for scientific discovery.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

WE-DE-BRA-11: A Study of Motion Tracking Accuracy of Robotic Radiosurgery Using a Novel CCD Camera Based End-To-End Test System

Purpose: A novel end-to-end test system using a CCD camera and a scintillator based phantom (XRV-124, Logos Systems Int’l) capable of measuring the beam-by-beam delivery accuracy of Robotic Radiosurgery (CyberKnife) was developed and reported in our previous work. This work investigates its application in assessing the motion tracking (Synchrony) accuracy for CyberKnife. Methods: A QA plan with Anterior and Lateral beams (with 4 different collimator sizes) was created (Multiplan v5.3) for the XRV-124 phantom. The phantom was placed on a motion platform (superior and inferior movement), and the plans were delivered on the CyberKnife M6 system using four motion patterns: static, Sine- wave, Sine with 15° phase shift, and a patient breathing pattern composed of 2cm maximum motion with 4 second breathing cycle. Under integral recording mode, the time-averaged beam vectors (X, Y, Z) were measured by the phantom and compared with static delivery. In dynamic recording mode, the beam spots were recorded at a rate of 10 frames/second. The beam vector deviation from average position was evaluated against the various breathing patterns. Results: The average beam position of the six deliveries with no motion and three deliveries with Synchrony tracking on ideal motion (sinewave without phase shift) all agree within −0.03±0.00 mm, 0.10±0.04, and 0.04±0.03 in the X, Y, and X directions. Radiation beam width (FWHM) variations are within ±0.03 mm. Dynamic video record showed submillimeter tracking stability for both regular and irregular breathing pattern; however the tracking error up to 3.5 mm was observed when a 15 degree phase shift was introduced. Conclusion: The XRV-124 system is able to provide 3D and 4D targeting accuracy for CyberKnife delivery with Synchrony. The experimental results showed sub-millimeter delivery in phantom with excellent correlation in target to breathing motion. The accuracy was degraded when irregular motion and phase shift was introduced.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

Phase-space moment-equation model of highly relativistic electron-beams in plasma-wakefield accelerators

We formulate a new procedure for modelling the transverse dynamics of relativistic electron beams with significant energy spread when injected into plasma-based accelerators operated in the blow-out regime. Quantities of physical interest, such as the emittance, are furnished directly from solution of phase space moment equations formed from the relativistic Vlasov equation. The moment equations are closed by an Ansatz, and solved analytically for prescribed wakefields. The accuracy of the analytic formulas is established by benchmarking against the results of a semi-analytic/numerical procedure which is described within the scope of this work, and results from a simulation with the 3D quasi-static PIC code HiPACE.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Radiation defect dynamics in 3 C -, 4 H -, and 6 H -SiC studied by pulsed ion beams

Radiation damage behavior of SiC depends on its lattice structure. Here, we use a pulsed-ion-beam method to study defect interaction dynamics in 6H-SiC and damage buildup in 4H- and 6H-SiC irradiated at 100 °C with 500 keV Ar ions. These results are compared with previously reported data for Ar-ion-irradiated 3C- and 4H-SiC. We find that, for these irradiation conditions, damage buildup in 3C- and 6H-SiC is statistically indistinguishable and is significantly more efficient than in 4H-SiC. Within a stimulated amorphization model, 4H-SiC is described by a reduced amorphization cross-section constant, while the point defect cluster production cross-section is the same (within experimental errors) for the three polytypes studied. Moreover, 4H-SiC exhibits slower defect relaxation dynamics than 3C- and 6H-SiC. These results clearly demonstrate the importance of the lattice structure in damage buildup and defect interaction dynamics in SiC.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Modeling of diamond field emitter arrays for a compact source of high brightness electron beams

Many applications, such as compact accelerators and electron microscopy, demand high brightness electron beams with small source size and ultralow emittance. Diamond emitters manufactured with semiconductor processes can be employed in such compact beam sources. The micrometer-scale pyramid structure of the emitter allows enhancement of the external field compared to that at the substrate, leading to electron emission with small beam size. We investigate the dependence of the field enhancement on the shape of the emitter and the resulting emission characteristics. The beam formation and dynamics are simulated with the LSP particle-in-cell code to obtain the macroscopic observables. To account for the semiconductor charge transport in the bulk material and the tunneling through the surface, a first-principle semiclassical Monte Carlo emission model is developed and applied to the diamond pyramid. Using this Monte Carlo emission model and the result from the geometric field enhancement calculation, we construct a simple model to qualitatively explain the measured emission characteristics. In conclusion, a comparison between our model and experiments indicates that the beam current is mostly emitted at the apex of the emitter.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Multichannel dynamics in the OH+ n -butane reaction revealed by crossed-beam slice imaging and quasiclassical trajectory calculations

Multidimensional reactions present various channels that can exhibit very different dynamics and give products of varying subsequent reactivity. Here, we present a combination of experiment and theory to reveal the dynamics of hydrogen abstraction by OH radical at primary and secondary sites in n-butane at a collision energy of 8 kcal/mol. Crossed molecular beam slice imaging experiments unequivocally probe the secondary abstraction channel showing backward angular distributions with mild energy release to product translation, which are accurately captured by trajectory calculations using a specific-reaction-parameter Hamiltonian. Additionally, experiments containing both reaction channels indicate a less marked backward character in the angular distribution, whose origin is shown by trajectory calculations to appear as an evolution toward more sideways scattering from the secondary to primary channel. While the two channels have markedly different angular distributions, their energy release is largely comparable, showing ample energy release into the water product. The synergistic combination of crossed-beam imaging and trajectories opens the door to detailed reaction-dynamics studies of chemical reactions with ever-increasing complexity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1967

Matrix Analysis of Longitudinal and Torsional Vibrations in Nonuniform Multibranch Beams

Since longitudinal modes and frequencies provide basic data for dynamic analyses of arbitrary beam-like structures and since closed-form solutions for the modes are generally not feasible to obtain, an approximate method is developed for computing the natural frequencies and the corresponding mode shapes for a variable-section, unconstrained multibranch beam. A lumped mass analogy employing influence coefficients is used to represent the beam. The simultaneous equations of motion for the lumped mass system are derived in matrix form and algebraically manipulated to yield a classical eigenvalue equation solvable by standard procedures. The orthogonality relationship of the natural modes is derived and used to form the basis of an orthogonal sweeping process for determination of modes above the fundamental. Numerical examples including an application to a solid-fuel launch system are presented. Also, a detailed discussion is devoted to the theoretical verifications of the approximate modes and frequencies.

Wingate, Robert T.↗

DOE OSTI2019

Radiation defect dynamics in SiC with pre-existing defects

The influence of pre-existing lattice disorder on radiation defect dynamics in SiC remains unexplored. Here, we use a pulsed ion beam method to study dynamic annealing in Ar-ion-bombarded 3C-SiC at 200°C with different levels of pre-existing lattice disorder. Results reveal a nonmonotonic dependence of the defect relaxation time constant on the level of pre-existing disorder, exhibiting a maximum of ~4 ms at a level of relative initial disorder of ~0.4, while crystals without pre-existing damage are characterized by a time constant of ~1.4 ms. These observations demonstrate that radiation defect dynamics in SiC can be controlled by defect engineering.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Nonlinear fishbone dynamics in spherical tokamaks

Linear and nonlinear kinetic-MHD hybrid simulations have been carried out to investigate linear stability and nonlinear dynamics of beam-driven fishbone instability in spherical tokamak plasmas. Realistic NSTX parameters with finite toroidal rotation were used. Our results show that the fishbone is driven by both trapped and passing particles. The instability drive of passing particles is comparable to that of trapped particles in the linear regime. The effects of rotation are destabilizing and a new region of instability appears at higher q min (>1.5) values, q min being the minimum of safety factor profile. In the nonlinear regime, the mode saturates due to flattening of beam ion distribution, and this persists after initial saturation while mode frequency chirps down in such a way that the resonant trapped particles move out radially and keep in resonance with the mode. Correspondingly, the flattening region of beam ion distribution expands radially outward. Furthermore, a substantial fraction of initially non-resonant trapped particles become resonant around the time of mode saturation and keep in resonance with the mode as frequency chirps down. On the other hand, the fraction of resonant passing particles is significantly smaller than that of trapped particles. Finally, our analysis shows that trapped particles provide the main drive to the mode in the nonlinear regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2017

Nonlinear fishbone dynamics in spherical tokamaks

Linear and nonlinear kinetic-MHD hybrid simulations have been carried out to investigate linear stability and nonlinear dynamics of beam-driven fishbone instability in spherical tokamak plasmas. Realistic NSTX parameters with finite toroidal rotation were used. The results show that the fishbone is driven by both trapped and passing particles. The instability drive of passing particles is comparable to that of trapped particles in the linear regime. The effects of rotation are destabilizing and a new region of instability appears at higher q min (>1.5) values, q min being the minimum of safety factor profile. In the nonlinear regime, the mode saturates due to flattening of beam ion distribution, and this persists after initial saturation while mode frequency chirps down in such a way that the resonant trapped particles move out radially and keep in resonance with the mode. Correspondingly, the flattening region of beam ion distribution expands radially outward. A substantial fraction of initially non-resonant trapped particles become resonant around the time of mode saturation and keep in resonance with the mode as frequency chirps down. On the other hand, the fraction of resonant passing particles is significantly smaller than that of trapped particles. Our analysis shows that trapped particles provide the main drive to the mode in the nonlinear regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2021

Space-Charge Aberrations in Single-Shot Time-Resolved Transmission Electron Microscopy

In this paper, we discuss effects of space-charge fields on imaging performance in a single-shot time-resolved transmission electron microscope. Using a Green’s function perturbation method, we derive analytical estimates for the effects of space-charge nonlinearity on the image formation process and the associated aberration coefficients. The dependence of these coefficients on the initial beam phase space distribution is elucidated. The results are validated by particle tracking simulations and provide fundamental scaling laws for the trade-off between temporal and spatial resolutions in single-shot time-resolved transmission electron microscopy.

43 PARTICLE ACCELERATORS↗