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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Feasibility of RACT for 3D dose measurement and range verification in a water phantom

Purpose: The objective of this study is to establish the feasibility of using radiation-induced acoustics to measure the range and Bragg peak dose from a pulsed proton beam. Simulation studies implementing a prototype scanner design based on computed tomographic methods were performed to investigate the sensitivity to proton range and integral dose. Methods: Derived from thermodynamic wave equation, the pressure signals generated from the dose deposited from a pulsed proton beam with a 1 cm lateral beam width and a range of 16, 20, and 27 cm in water using Monte Carlo methods were simulated. The resulting dosimetric images were reconstructed implementing a 3D filtered backprojection algorithm and the pressure signals acquired from a 71-transducer array with a cylindrical geometry (30 × 40 cm) rotated over 2π about its central axis. Dependencies on the detector bandwidth and proton beam pulse width were performed, after which, different noise levels were added to the detector signals (using 1 μs pulse width and a 0.5 MHz cutoff frequency/hydrophone) to investigate the statistical and systematic errors in the proton range (at 20 cm) and Bragg peak dose (of 1 cGy). Results: The reconstructed radioacoustic computed tomographic image intensity was shown to be linearly correlated to the dose within the Bragg peak. And, based on noise dependent studies, a detector sensitivity of 38 mPa was necessary to determine the proton range to within 1.0 mm (full-width at half-maximum) (systematic error < 150 μm) for a 1 cGy Bragg peak dose, where the integral dose within the Bragg peak was measured to within 2%. For existing hydrophone detector sensitivities, a Bragg peak dose of 1.6 cGy is possible. Conclusions: This study demonstrates that computed tomographic scanner based on ionizing radiation-induced acoustics can be used to verify dose distribution and proton range with centi-Gray sensitivity. Realizing this technology into the clinic has the potential to significantly impact beam commissioning, treatment verification during particle beam therapy and image guided techniques.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

SU-E-T-571: Newly Emerging Integrated Transmission Detector Systems Provide Online Quality Assurance of External Beam Radiation Therapy

Purpose: Two newly emerging transmission detectors positioned upstream from the patient have been evaluated for online quality assurance of external beam radiotherapy. The prototype for the Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large-area ion chamber mounted on the linac accessory tray to monitor photon fluence, energy, beam shape, and gantry position during treatment. The ion chamber utilizes a thickness gradient which records variable response dependent on beam position. The prototype of Delta4 Discover™, developed by ScandiDos (Uppsala, Sweden) is a linac accessory tray mounted 4040 diode array that measures photon fluence during patient treatment. Both systems are employable for patient specific QA prior to treatment delivery. Methods: Our institution evaluated the reproducibility of measurements using various beam types, including VMAT treatment plans with both the IQM ion chamber and the Delta4 Discover diode array. Additionally, the IQM’s effect on photon fluence, dose response, simulated beam error detection, and the accuracy of the integrated barometer, thermometer, and inclinometer were characterized. The evaluated photon beam errors are based on the annual tolerances specified in AAPM TG-142. Results: Repeated VMAT treatments were measured with 0.16% reproducibility by the IQM and 0.55% reproducibility by the Delta4 Discover. The IQM attenuated 6, 10, and 15 MV photon beams by 5.43±0.02%, 4.60±0.02%, and 4.21±0.03% respectively. Photon beam profiles were affected <1.5% in the non-penumbra regions. The IQM’s ion chamber’s dose response was linear and the thermometer, barometer, and inclinometer agreed with other calibrated devices. The device detected variations in monitor units delivered (1%), field position (3mm), single MLC leaf positions (13mm), and photon energy. Conclusion: We have characterized two new transmissions detector systems designed to provide in-vivo like measurements upstream from the patient. Both systems demonstrate substantial utility for online treatment verification and QA of photon external beam radiotherapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

SU-D-BRE-05: Feasibility and Limitations of Laser-Driven Proton Therapy: A Treatment Planning Study

Purpose: Laser-acceleration of particles may offer a cost- and spaceefficient alternative for future radiation therapy with particles. Laser-driven particle beams are pulsed with very short bunch times, and a high number of particles is delivered within one laser shot which cannot be portioned or modulated during irradiation. The goal of this study was to examine whether good treatment plans can be produced for laser-driven proton beams and to investigate the feasibility of a laser-driven treatment unit. Methods: An exponentially decaying proton spectrum was tracked through a gantry and energy selection beam line design to produce multiple proton spectra with different energy widths centered on various nominal energies. These spectra were fed into a treatment planning system to calculate spot scanning proton plans using different lateral widths of the beam and different numbers of protons contained in the initial spectrum. The clinical feasibility of the resulting plans was analyzed in terms of dosimetric quality and the required number of laser shots as an estimation of the overall treatment time. Results: We were able to produce treatment plans with plan qualities of clinical relevance for a maximum initial proton number per laser shot of 6*10{sup 8}. However, the associated minimum number of laser shots was in the order of 10{sup 4}, indicating a long delivery time in the order of at least 15 minutes, when assuming an optimistic repetition rate of the laser system of 10 Hz. Conclusion: With the simulated beam line and the assumed shape of the proton spectrum it was impossible to produce clinically acceptable treatment plans that can be delivered in a reasonable time. The situation can be improved by a method or a device in the beam line which can modulate the number of protons from shot to shot. Supported by DFG Cluster of Excellence: Munich-Centre for Advanced Photonics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1990

Advances in atomic oxygen simulation

Atomic oxygen (AO) present in the atmosphere at orbital altitudes of 200 to 700 km has been shown to degrade various exposed materials on Shuttle flights. The relative velocity of the AO with the spacecraft, together with the AO density, combine to yield an environment consisting of a 5 eV beam energy with a flux of 10(exp 14) to 10(exp 15) oxygen atoms/sq cm/s. An AO ion beam apparatus that produces flux levels and energy similar to that encountered by spacecraft in low Earth orbit (LEO) has been in existence since 1987. Test data was obtained from the interaction of the AO ion beam with materials used in space applications (carbon, silver, kapton) and with several special coatings of interest deposited on various surfaces. The ultimate design goal of the AO beam simulation device is to produce neutral AO at sufficient flux levels to replicate on-orbit conditions. A newly acquired mass spectrometer with energy discrimination has allowed 5 eV neutral oxygen atoms to be separated and detected from the background of thermal oxygen atoms of approx 0.2 eV. Neutralization of the AO ion beam at 5 eV was shown at the Martin Marietta AO facility.

Froechtenigt, Joseph F.↗
DOE OSTI2017

Nonlinear simulations of beam-driven Compressional Alfv´en Eigenmodes in NSTX

We present results for the 3D nonlinear simulations of neutral-beam-driven compressional Alfv´en eigenmodes (CAEs) in the National Spherical Torus Experiment (NSTX). Hybrid MHD-particle simulations for the H-mode NSTX discharge (shot 141398) using the HYM code show unstable CAE modes for a range of toroidal mode numbers, n = 4 - 9, and frequencies below the ion cyclotron frequency. It is found that the essential feature of CAEs is their coupling to kinetic Alfv´en wave (KAW) that occurs on the high-field side at the Alfv´en resonance location. We frequently observe high-frequency Alfv´en eigenmodes in beam-heated NSTX plasmas, and have been linked to flattening of the electron temperature profiles at high beam power. Coupling between CAE and KAW suggests an energy channeling mechanism to explain these observations, in which beam driven CAEs dissipate their energy at the resonance location, therefore significantly modifying the energy deposition profile. Nonlinear simulations demonstrate that CAEs can channel the energy of the beam ions from the injection region near the magnetic axis to the location of the resonant mode conversion at the edge of the beam density profile. Furthermore, a set of nonlinear simulations show that the CAE instability saturates due to nonlinear particle trapping, and a large fraction of beam energy can be transferred to several unstable CAEs of relatively large amplitudes and absorbed at the resonant location. Absorption rate shows a strong scaling with the beam power.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Simulation of ion beam transport through the 400 Kv ion implanter at Michigan Ion Beam Laboratory

The Michigan Ion Beam Laboratory houses a 400 kV ion implanter. An application that simulates the ion beam trajectories through the implanter from the ion source to the target was developed using the SIMION Registered-Sign code. The goals were to have a tool to develop an intuitive understanding of abstract physics phenomena and diagnose ion trajectories. Using this application, new implanter users of different fields in science quickly understand how the machine works and quickly learn to operate it. In this article we describe the implanter simulation application and compare the parameters of the implanter components obtained from the simulations with the measured ones. The overall agreement between the simulated and measured values of magnetic fields and electric potentials is {approx}10%.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Physics-constrained machine learning for electrodynamics without gauge ambiguity based on Fourier transformed Maxwell’s equations

We utilize a Fourier transformation-based representation of Maxwell’s equations to develop physics-constrained neural networks for electrodynamics without gauge ambiguity, which we label the Fourier–Helmholtz–Maxwell neural operator method. In this approach, both of Gauss’s laws and Faraday’s law are built in as hard constraints, as well as the longitudinal component of Ampère–Maxwell in Fourier space, assuming the continuity equation. An encoder–decoder network acts as a solution operator for the transverse components of the Fourier transformed vector potential, $\hat{A}_⟂(k,t)$, whose two degrees of freedom are used to predict the electromagnetic fields. This method was tested on two electron beam simulations. Among the models investigated, it was found that a U-Net architecture exhibited the best performance as it trained quicker, was more accurate and generalized better than the other architectures examined. We demonstrate that our approach is useful for solving Maxwell’s equations for the electromagnetic fields generated by intense relativistic charged particle beams and that it generalizes well to unseen test data, while being orders of magnitude quicker than conventional simulations. We show that the model can be re-trained to make highly accurate predictions in as few as 20 epochs on a previously unseen data set.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

The Boersch effect in a picosecond pulsed electron beam emitted from a semiconductor photocathode

The space charge effect has been clearly observed in the energy distributions of picosecond pulse beams from a spin-polarized electron microscope, and was found to depend upon the quantity of charge per pulse. The non-linear phenomena associated with this effect have also been replicated in beam simulations that take into account of a three-dimensional space charge. The results show that a charge of 500 aC/pulse provides the highest brightness with a 16-ps pulse duration, a 30-keV beam energy, and an emission spot of 1.8 μm. Furthermore, the degeneracy of the wave packet of the pulsed electron beam has been evaluated to be 1.6 × 10{sup −5} with a charge of 100 aC/pulse, which is higher than that for a continuously emitted electron beam despite the low beam energy of 30 keV. The high degeneracy and high brightness contribute to the realization of high temporal and energy resolutions in low-voltage electron microscopy, which will serve to reduce radiolysis damage and enhance scattering contrast.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

SU-E-T-241: Monte Carlo Simulation Study About the Prediction of Proton-Induced DNA Strand Breakage On the Double Helix Structure

Purpose: In particle therapy and radiobiology, the investigation of mechanisms leading to the death of target cancer cells induced by ionising radiation is an active field of research. Recently, several studies based on Monte Carlo simulation codes have been initiated in order to simulate physical interactions of ionising particles at cellular scale and in DNA. Geant4-DNA is the one of them; it is an extension of the general purpose Geant4 Monte Carlo simulation toolkit for the simulation of physical interactions at sub-micrometre scale. In this study, we present Geant4-DNA Monte Carlo simulations for the prediction of DNA strand breakage using a geometrical modelling of DNA structure. Methods: For the simulation of DNA strand breakage, we developed a specific DNA geometrical structure. This structure consists of DNA components, such as the deoxynucleotide pairs, the DNA double helix, the nucleosomes and the chromatin fibre. Each component is made of water because the cross sections models currently available in Geant4-DNA for protons apply to liquid water only. Also, at the macroscopic-scale, protons were generated with various energies available for proton therapy at the National Cancer Center, obtained using validated proton beam simulations developed in previous studies. These multi-scale simulations were combined for the validation of Geant4-DNA in radiobiology. Results: In the double helix structure, the deposited energy in a strand allowed to determine direct DNA damage from physical interaction. In other words, the amount of dose and frequency of damage in microscopic geometries was related to direct radiobiological effect. Conclusion: In this report, we calculated the frequency of DNA strand breakage using Geant4- DNA physics processes for liquid water. This study is now on-going in order to develop geometries which use realistic DNA material, instead of liquid water. This will be tested as soon as cross sections for DNA material become available in Geant4-DNA.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Study of Spherical Array Target for Long-Baseline Neutrino Experiment

Spherical Array Target was studied by implementing the geometry in LBNE's Beam Simulation source code g4lbne version v3r2p4 and Monte Carlo. To compare with Nominal LBNE target, unoscillated Far Detector neutrino flux was produced using different parameters: sphere diameter 17mm and 13mm, different longitudinal positions, two interaction length and less, beam size R/3 and 1.7mm, and beam offset from 50 $\mu$m to 1mm. The 1.86 interaction length (901mm), 17mm diameter target, with beam size 1.7mm gives higher $\nu_{\mu}$ flux up to 10% from 0-3.5 GeV, and suppresses flux up to 70% at energy higher than 3.5 GeV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Feasibility study of real-time planning for stereotactic radiosurgery

Purpose: 3D rotational setup errors in radiotherapy are often ignored by most clinics due to inability to correct or simulate them accurately and efficiently. There are two types of rotation-related problems in a clinical setting. One is to assess the affected dose distribution in real-time if correction is not applied and the other one is to correct the rotational setup errors prior to the initiation of the treatment. Here, the authors present the analytical solutions to both problems. Methods: (1) To assess the real-time dose distribution, eight stereotactic radiosurgery (SRS) cases were used as examples. For each plan, two new sets of beams with different table, gantry, and collimator angles were given in analytical forms as a function of patient rotational errors. The new beams simulate the rotational effects of the patient during the treatment setup. By using one arbitrary set of beams, SRS plans were recomputed with a series of different combinations of patient rotational errors, ranging from (-5 Degree-Sign , -5 Degree-Sign , -5 Degree-Sign ) to (5 Degree-Sign , 5 Degree-Sign , 5 Degree-Sign ) (roll, pitch, and yaw) with an increment of 1 Degree-Sign and compared with those without rotational errors. For each set of rotational errors, its corresponding equivalent beams were computed using the analytical solutions and then used for dose calculation. (2) To correct for the rotational errors, two new sets of table, gantry, and collimator angles were derived analytically to validate the previously published derivation. However, in the derivation, a novel methodology was developed and two sets of table, gantry, and collimator angles were obtained in analytical forms. The solutions provide an alternative approach to rotational error correction by rotating the couch, gantry, and collimator rather than the patient. Results: For demonstration purpose, the above-derived new beams were implemented in a treatment planning system (TPS) to study the rotational effects on the SRS cases. For each case, the authors have generated ten additional plans that accounted for different rotations of the patient. They have found that rotations have an insignificant effect on the minimal, maximum, mean doses, and V{sub 80%} of the planning target volume (PTV) when the rotations were relatively small. This was particularly true for the small and near-spherical targets. They, however, did change V{sub 95%} significantly when the rotations approached 5 Degree-Sign . The theory has been validated with clinical SRS cases and proven to be practical and viable. The preliminary results demonstrate that the rotational effects are patient-specific and depend on several important factors, such as the PTV size, the PTV location, and the beam configuration. The solutions given in this paper are of great potential values in clinical applications. Conclusions: They have derived the analytical solutions to a new set of table, gantry, and collimator angles for a given treatment beam configuration as a function of patient rotational errors. One solution was used to assess the dosimetric effects of an imperfect patient setup and the other one was used to correct for the setup errors without rotating the patient. Compared to the widely adopted method of rotation effect assessment by importing the rotational CT images into TPS, the equivalent beam approach is simple and accurate. The analytical solutions to correcting for rotational setup errors prior to treatment were also derived. Based on the initial clinical investigations, they firmly believe that clinically viable real-time treatment planning and adaptive radiation therapy are feasible with this novel method.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1981

Numerical simulation of the generation of electrostatic turbulence in the magnetotail

A two-dimensional plasma model is used to investigate the development of electrostatic turbulence in a magnetized plasma from plasma instabilities. The simulation consists of following the motion of 100,000 ions in their self-consistent electrostatic field. The electrons are treated as a constant neutralizing background. The instabilities modeled are driven by a ring-type velocity distribution and by interpenetrating ion beams in a time-variable magnetic field. Instability growth times are of the order of an ion gyroperiod in the case of the ring distribution and of the order of an ion plasma period in the case of the beam simulation. Maximum potential differences generated are of the order of the ion kinetic energies. These simulations demonstrate the cascade of wave energy to long wavelengths, thus showing the E x B turbulence can be generated from plasma microinstabilities. After the free energy feeding, the instabilities are exhausted, and wave energy at wavelengths less than an ion gyrodiameter decays quickly to equilibrium levels, while longer wavelength modes persist for much longer times. In one model with a time dependent, but spatially uniform, magnetic field the electric field energy at long wavelengths appeared to increase as a result of the increase of the magnetic field.

Swift, D. W.↗
DOE OSTI2020

Evaluating Energy Efficiency Opportunities from Connected and Automated Vehicle Deployments Coupled with Shared Mobility in California

Connected and Automated Vehicles (CAVs) can be considered to be a disruptive transportation technology, with the potential to significantly improve overall transportation system efficiency; however, CAVs may increase induce vehicle miles traveled (VMT) and bring on greater energy consumption. Further, shared mobility is another disruptive transportation event that is reshaping our travel patterns. The primary goal of this project was to extensively collect data from vehicles and associated infrastructure equipped with CAV technologies from both real-world experiments and simulation studies mainly deployed in California, and develop a comprehensive framework for evaluating energy efficiency opportunities from large-scale (e.g., statewide) introduction of CAVs and a wide deployment of shared mobility systems in a variety of scenarios. To quantify the combined impact of CAV and shared mobility on travel behavior, traffic performance, and energy efficiency, a unique mesoscopic simulation-based model was developed for mobility and energy efficiency evaluation considering these disruptive transportation technologies. As a complement to existing studies on nationwide evaluation of CAVs’ energy impacts, this project was focused on data collection efforts and CAV applications under congested traffic environments that are frequently experienced on a massive scale across the major metropolitan areas in California. Extensive real-world data collection supplemented with simulation studies were conducted to cover a variety of CAV and shared mobility scenarios, particularly on scenarios less-explored in the existing research. Another key component of this project was to consider the interaction between different CAV technologies and shared mobility models, and the compound effect on energy efficiency. A comprehensive modeling suite was developed to quantify the impact of new mobility technologies on travel behavior and traffic performance. The developed modeling framework includes an energy intensity module, mode choice module and activity generation module that are integrated into an agent-based BEAM simulation platform to perform impact analysis based on a variety of scenarios. In addition, the RouteE model has been upgraded to incorporate the impact of CAVs on traffic flow, VMT and energy intensity, using micro-simulation data collected from both freeways and urban arterials. A novel fundamental influencing factor (FIF) mode choice model was developed to link CAV and shared mobility components with travel behaviors, and adapted into the BEAM-centered model framework. A statewide energy inventory was constructed under various CAV technology deployment scenarios by incorporating datasets and models for predicting vehicle market share and vehicle usage, which are tightly associated with the penetration of shared mobility systems. Based applying this modeling suite to a calibrated network in Riverside California, it was found that cooperative automated driving in general will improve mobility, but automated vehicles, even when deployed in a shared autonomous fleet, will likely bring an increase of VMT (up to 36%) due to mode shifts and deadheading. Ride-hailing vehicles typically have better energy efficiency and a higher share of electric vehicles, which helps offset the negative impact from VMT increases when estimating the system-level energy consumption. In general, simulation results show a 6% increase in energy consumption for the scenarios with an increasing shift to ride-hailing modes. The statewide analysis based on the National Household Travel Survey (NHTS) sample data is consistent with the findings from the Riverside network and validate the developed clustering-prediction modeling methodology. The outcomes from this project will help close the knowledge gap on recognizing the potential performance and energy impacts of a broad deployment of CAV and shared mobility technologies across a wide range of roadway infrastructure with varying levels of congestion. Results from this project: 1) will support policymakers in steering CAV development and deployment towards an energy favorable direction; 2) reduce uncertainties in estimating energy saving opportunities from new mobility technologies and services; 3) increase the confidence of CAV technology investors both on the infrastructure side (i.e., transportation agencies) and on the vehicle side (i.e., OEMs); and 4) expedite the deployment of energy-efficient CAV and shared mobility applications.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2015

Collective Effects in a Diffraction Limited Storage Ring

Our paper gives an overview of collective effects that are likely to appear and possibly limit the performance in a diffraction-limited storage ring (DLSR) that stores a high-intensity ultra-low-emittance beam. Beam instabilities and other intensity-dependent effects that may significantly impact the machine performance are covered. The latter include beam-induced machine heating, Touschek scattering, intra-beam scattering, as well as incoherent tune shifts. The general trend that the efforts to achieve ultra-low emittance result in increasing the machine coupling impedance and the beam sensitivity to instability is reviewed. The nature of coupling impedance in a DLSR is described, followed by a series of potentially dangerous beam instabilities driven by the former, such as resistive-wall, TMCI (transverse mode coupling instability), head-tail and microwave instabilities. Additionally, beam-ion and CSR (coherent synchrotron radiation) instabilities are also treated. Means to fight against collective effects such as lengthening of the bunch with passive harmonic cavities and bunch-by-bunch transverse feedback are introduced. Numerical codes developed and used to evaluate the machine coupling impedance, as well as to simulate beam instability using the former as inputs are described.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Linac_Gen: Integrating Machine Learning and Particle-in-Cell Methods for Enhanced Beam Dynamics at Fermilab

Here, we introduce Linac_Gen, a tool developed at Fermilab, which combines machine learning algorithms with Particle-in-Cell methods to advance beam dynamics in linacs. Linac_Gen employs techniques such as Random Forest, Genetic Algorithms, Support Vector Machines, and Neural Networks, achieving a tenfold increase in speed for phase-space matching in Linacs over traditional methods, through the use of genetic algorithms. Crucially, Linac_Gen's adept handling of 3D field maps elevates the precision and realism in simulating beam instabilities and resonances, marking a key advancement in the field. Benchmarked against established codes, Linac_Gen demonstrates not only improved efficiency and precision in beam dynamics studies but also in the design and optimization of Linac systems, as evidenced in its application to Fermilab's PIP-II Linac project. This work represents a notable advancement in accelerator physics, marrying ML with PIC methods to set new standards for efficiency and accuracy in accelerator design and research. Linac_Gen exemplifies a novel approach in accelerator technology, offering substantial improvements in both theoretical and practical aspects of beam dynamics.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Linac_Gen: integrating machine learning and particle-in-cell methods for enhanced beam dynamics at Fermilab

Here, we introduce Linac_Gen, a tool developed at Fermilab, which combines machine learning algorithms with Particle-in-Cell methods to advance beam dynamics in linacs. Linac_Gen employs techniques such as Random Forest, Genetic Algorithms, Support Vector Machines, and Neural Networks, achieving a tenfold increase in speed for phase-space matching in linacs over traditional methods through the use of genetic algorithms. Crucially, Linac_Gen's adept handling of 3D field maps elevates the precision and realism in simulating beam instabilities and resonances, marking a key advancement in the field. Benchmarked against established codes, Linac_Gen demonstrates not only improved efficiency and precision in beam dynamics studies but also in the design and optimization of linac systems, as evidenced in its application to Fermilab's PIP-II linac project. This work represents a notable advancement in accelerator physics, marrying ML with PIC methods to set new standards for efficiency and accuracy in accelerator design and research. Linac_Gen exemplifies a novel approach in accelerator technology, offering substantial improvements in both theoretical and practical aspects of beam dynamics.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Evaluate the System-Level Impact of Connected and Automated Vehicles Coupled with Shared Mobility: An Agent-based Simulation Approach

With the rapid growth of information and communication technologies, Connected and Automated Vehicles (CAVs) are deemed to be disruptive with the potential to significantly improve overall transportation system efficiency, however, may bring Vehicle Miles Traveled (VMT) increase or other issues. Further, shared mobility systems are another disruptive force that is reshaping our travel patterns. To quantify the combined impact of CAV and shared mobility on travel behavior, traffic performance and energy efficiency, we develop a mesoscopic simulation-based framework for mobility and energy efficiency evaluation considering the disruptive transportation technologies. Under this framework, we develop novel models for energy intensity and modal activity, and evaluated a variety of energy scenarios for different combinations of CAV applications, various levels of automation, roadway characteristics, and traffic conditions, while also varying different vehicle types and fuel/powertrain technologies. Based applying this modeling suite to a calibrated BEAM simulation network in Riverside California, it was found that cooperative automated driving in general will improve mobility, but automated vehicles, even when deployed in a shared autonomous fleet, will likely bring an increase of VMT (up to 36%) due to mode shifts and deadheading. Ride-hailing vehicles typically have better energy efficiency and a higher share of electric vehicles, which helps offset the negative impact from VMT increases when estimating the system-level energy consumption. In general, simulation results show a 6% increase in energy consumption for the scenarios with an increasing shift to ride-hailing modes.

42 ENGINEERING↗
DOE OSTI2018

ALTERNATIVE CONFIGURATION AND TIMING CONTROL FOR BEAM CHOPPING SYSTEM AT THE SNS LINAC

The Spallation Neutron Source (SNS) beam chopping system uses a segmented electrostatic lens in the Low Energy Beam Transport (LEBT) line to deflect the beam out of the Radio Frequency Quadrupole (RFQ) input aperture to create gaps in the 1 ms beam macro-pulse for extraction from the Ring, or fully displace the beam. The lens is split azimuthally into four quadrants which are pulsed independently by four bipolar high voltage pulse generators. The chopper timing control system creates trigger pulses to the pulse generators which deflect the beam sequentially to four positions on the chopper target. In the present chopper configuration, all four segments are powered simultaneously with a 1 MHz burst repetition rate within the macro-pulse. To improve chopping performance, faster switches and higher voltages are required. An alternative chopping system configuration which can meet this request has been proposed, where only two opposite segments are used at a time. This will facilitate pulse generator performance by reducing switching frequency and power dissipation in the high voltage switches while operating at increased voltages, and make beam deflection more effective, stable and reliable. The new chopping configuration requires changes in the LEBT timing control patterns, upgrading the pulse generator, and changing the azimuthal position of the lens segments in the LEBT structure.This paper will review the timing control patterns for present and suggested configurations, compare the pulse generator performance for both cases, and show the advantages of the new chopping modes. The results of the simulated beam distribution at the RFQ input for different deflecting voltages will also be presented.

Peplov, Vladimir↗