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DOE OSTI2018

On-Chip Laser-Power Delivery System for Dielectric Laser Accelerators

We propose an on-chip optical-power delivery system for dielectric laser accelerators based on a fractal “tree-network” dielectric waveguide geometry. Here, this system replaces experimentally demanding free-space manipulations of the driving laser beam with chip-integrated techniques based on precise nanofabrication, enabling access to orders-of-magnitude increases in the interaction length and total energy gain for these miniature accelerators. Based on computational modeling, in the relativistic regime, our laser delivery system is estimated to provide 21 keV of energy gain over an acceleration length of 192 μm with a single laser input, corresponding to a 108-MV/m acceleration gradient. The system may achieve 1 MeV of energy gain over a distance of less than 1 cm by sequentially illuminating 49 identical structures. These findings are verified by detailed numerical simulation and modeling of the subcomponents, and we provide a discussion of the main constraints, challenges, and relevant parameters with regard to on-chip laser coupling for dielectric laser accelerators.

43 PARTICLE ACCELERATORS↗

DOE OSTI2022

Velocity-space compression from Fermi acceleration with Lorentz scattering

The Fermi acceleration model describes how cosmic ray particles accelerate to great speeds by interacting with moving magnetic fields. In this work, we identify a variation of the model where light ions interact with a moving wall while undergoing pitch angle scattering through Coulomb collisions due to the presence of a heavier ionic species. The collisions introduce a stochastic component which adds complexity to the particle acceleration profile and sets it apart from collisionless Fermi acceleration models. The unusual effect captured by this simplified variation of Fermi acceleration is the nonconservation of phase space, with the possibility for a distribution of particles initially monotonically decreasing in energy to exhibit an energy peak upon compression. A peaked energy distribution might have interesting applications, such as to optimize fusion reactivity or to characterize astrophysical phenomena that exhibit nonthermal features.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Accelerator commissioning and rare isotope identification at the Facility for Rare Isotope Beams

In 2008, Michigan State University was selected to establish the Facility for Rare Isotope Beams (FRIB). Construction of the FRIB accelerator was completed in January 2022. Phased accelerator commissioning with heavy ion beams started in 2017 with the normal-conducting ion source and radio-frequency quadrupole. In April 2021, the full FRIB driver linear accelerator (linac) was commissioned, with heavy ion beams accelerated to energies above 200 MeV/nucleon by 324 superconducting radiofrequency (SRF) resonators operating at 2 K and 4 K with liquid-helium cooling. Further, in preparation for high-power operation, a liquid lithium charge stripper was commissioned with heavy ion beams up to uranium-238, followed by the simultaneous acceleration of multiple-charge-state heavy ion beams to energies above 200 MeV/nucleon. In December 2021, selenium-84 was produced with the FRIB target using a krypton-86 primary beam, demonstrating FRIB’s capability for scientific discovery.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2025

Extending JuTrack’s capabilities to the FRIB accelerator to enhance online modeling

JuTrack is a Julia-based accelerator modeling and tracking package that utilizes compiler-level automatic differentiation (AD) to enable fast and accurate derivative calculations. While JuTrack provides a solid foundation for beam dynamics simulations, its capabilities must be extended to support the Facility for Rare Isotopes (FRIB) linac. This includes modeling heavy-ion linac accelerator components such as the liquid-lithium charge stripper, which facilitates efficient acceleration by remove electrons from heavy isotopes, and incorporating multi-charge state acceleration tracking, which allows for charge-dependent beam dynamics. These extensions address challenges such as the beam matching and optimization of multi charge state through various accelerating structures and beam-material interaction modeling while maintaining the auto differentiation capability. This work focuses on adapting JuTrack to incorporate these elements, enhancing its online modeling abilities. We present modifications to JuTrack’s framework and demonstrate their performance in FRIB simulations.

Accelerator Physics↗

DOE OSTI2020

Accelerated epigenetic aging as a risk factor for chronic obstructive pulmonary disease and decreased lung function in two prospective cohort studies

Chronic obstructive pulmonary disease (COPD) is a frequent diagnosis in older individuals and contributor to global morbidity and mortality. Given the link between lung disease and aging, we need to understand how molecular indicators of aging relate to lung function and disease. Using data from the population-based KORA (Cooperative Health Research in the Region of Augsburg) surveys, we associated baseline epigenetic (DNA methylation) age acceleration with incident COPD and lung function. Models were adjusted for age, sex, smoking, height, weight, and baseline lung disease as appropriate. Associations were replicated in the Normative Aging Study. Of 770 KORA participants, 131 developed incident COPD over 7 years. Baseline accelerated epigenetic aging was significantly associated with incident COPD. The change in age acceleration (follow-up – baseline) was more strongly associated with COPD than baseline aging alone. The association between the change in age acceleration between baseline and follow-up and incident COPD replicated in the Normative Aging Study. Associations with spirometric lung function parameters were weaker than those with COPD, but a meta-analysis of both cohorts provide suggestive evidence of associations. Accelerated epigenetic aging, both baseline measures and changes over time, may be a risk factor for COPD and reduced lung function.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2017

Organization of the 17th Advanced Accelerator Concepts (AAC16) Workshop by the IEEE. Final Scientific/Technical Report On AWARD NO. DE-SC0015635

The 2016 Workshop on Advanced Accelerator Concepts (AAC) was held at the Gaylord Hotel and Conference Center, National Harbor, Maryland, from July 31 through August 5, 2016. This workshop was the seventeenth in a biennial series that began at Los Alamos National Laboratory in 1982 with a workshop on laser acceleration of particles (see AIP Conf. Proc. 91). AAC16 was organized under the sponsorship of the IEEE Council on Superconductivity with financial support from the U. S. Department of Energy Office of High Energy Physics and the National Science Foundation. The scope of the AAC Workshop has grown since 1982 to encompass a broad range of topics related to advancing accelerator science and technology beyond its current scientific and technical limits and is now an internationally acknowledged forum for interdisciplinary discussions on advanced accelerator and beam physics/technology concepts covering the widest possible range of applications. The Workshop continued the trend of growing worldwide participation, attracting world wide participation. The Workshop had a total of 256 attendees comprising (including the U.S.) representatives from 11 countries representing 65 different institutions. Each day’s schedule began with plenary sessions covering broad, cross disciplinary interests or general tutorial topics as selected by the Program Committee, followed by a break out into more narrowly focused working groups. The Workshop was organized into eight Working Groups each with a published statement of topical focus, scope of discussion and goals. A summary of the Working Group activities and conclusions is included in the American Institute of Physics’ (AIP) Conference Proceedings now available as an on line open source document. It has been a long tradition of the AAC workshops to encourage strong student participation. This is accomplished in part by subsidizing student attendance, done for this work shop by using funds from the DOE and National Science Foundation to significantly reduce student registration fees. As a result the registered student participation was 75 persons, or 29% of the total attendance of 256 persons, the highest percentage student enrollment the Workshop has ever had. This is the final report for the DOE Office of Science/Office of High Energy Physics grant NO. DE-SC0015635, entitled “Organization of the17th Advanced Accelerator Concepts Workshop by the IEEE.”

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

High-current density CORC® wires for use in accelerator magnets

Next generation accelerator magnets capable of generating magnetic fields in excess of 16 T require high-temperature superconductors (HTS) such as Conductor on Round Core (CORC®) cables and wires, wound from RE-Ba 2 Ca 3 O 7-δ (ReBCO, Re = rare earth) coated conductor tapes.1 The severe operating requirements of an engineering current density (J e ) of at least 400 Amm -2 at 4.2 K and 20 T, high operating currents of 5-20 kA, tolerance to Lorentz stresses in excess of 150 MPa, and in many cases cable bending diameters as small as 30 mm, make accelerator magnets one of the most challenging applications for any HTS material. Advanced Conductor Technologies (ACT) has been developing CORC® cables and wires wound from ReBCO tapes containing substrates of 30-50 µm thickness to meet these requirements. Although these requirements could each be met separately with current CORC® technology, meeting the requirements at the same time requires thinner, more powerful CORC® wires wound from tapes with even thinner substrates. The purpose of this Phase I SBIR program was to determine the feasibility to develop ReBCO tapes containing 25 µm thick substrates on an industrial scale and wind thinner CORC® wires from these tapes that could eventually meet the stringent performance specifications for accelerator magnets. The results of the Phase I program clearly demonstrated the feasibility of developing thinner, more powerful CORC® wires using ReBCO tapes with 25 µm substrate that would likely meet the stringent requirements for use in accelerator magnet by the end of the potential Phase II program. SuperPower Inc., as the subcontractor on the Phase I program, was successful in developing tapes with 25 µm substrate at minimum piece lengths of 30-40 m with a clear path towards industrial production. A total length exceeding 350 meters of 2 mm wide ReBCO tape with critical current (I c ) of between 45 and 65 A at 77 K was delivered to ACT during the Phase I program. The thinner tapes allowed us to reduce the CORC® core (former) from 2.5 mm to 2.0 mm, resulting in a higher current density conductor with enhanced flexibility. Several CORC® wires were manufactured to reach the Phase I goal of a Je of at least 300-400 Amm -2 at 20 T at a minimum bending diameter to less than 50 mm. Several CORC® wires were wound and analyzed after bending by identifying the location of peak stresses and causes of tape damage. Data was compared to 3D finite element models that included parametric studies to identify key parameters leading to the observed tape failure modes. The models suggest that flexibility is heavily dependent on the friction coefficient between tapes in a CORC® wire and the width of the tapes used. These studies provide a clear and straightforward path to improve conductor flexibility within the proposed Phase II program to reach our goal of minimum bending diameters below 30 mm with minimal I c reduction. We were successful in developing a flexible, 3.3 mm thick, high-J e CORC® wire containing 30 ReBCO tapes that carried > 80 % of its original I c after bending to diameters down to 44 mm. The CORC® wires showed no cyclic degradation due to in-field testing up to 57 stress cycles at 12 T. Another CORC® wire of 3.4 mm thickness had a J e as high as 451 Amm -2 when extrapolated to 20 T at a bending diameter of 63 mm, which is a new high-field performance record. We were also able to design a CORC® wire with increased tensile strength of 240 MPa at 76 K. The results of the Phase I program allow us to propose a very strong Phase II program with a high likelihood of reaching the ultimate goal of CORC® accelerator magnets wires with I c exceeding 8-10 kA and J e exceeding 600 Amm -2 at 20 T while bent to a 30 mm diameter.

43 PARTICLE ACCELERATORS↗

DOE OSTI2021

Accelerator Real-time Edge AI for Distributed Systems (READS) (Proposal)

Over the last decade, Machine Learning (ML) technologies have slowly made their way into the accelerator community. Rapid advances in recent years in deep learning, particularly reinforcement learning for control system applications and the accessibility of deep learning in embedded hardware, have generated renewed interest and spawned a number of applications. The Fermilab Accelerator Complex, shown in Fig. 1, has provided High Energy Physics (HEP) experiments with proton beams for nearly fifty years. The current focus of the laboratory is its world-class experimental program at the intensity frontier. While increasing beam intensity certainly presents its own challenges, preserving beam size while minimizing beam losses – particles lost through interactions with the beam vacuum pipe – turns out to be, in many ways, the main challenge. The accelerator is controlled via a complex system of hundreds of thousands of devices. Enabling fine tuning and real-time optimization of their parameters using ML methods and stepping beyond experience-based reasoning of human operators are key to the success of future intensity upgrades. Our objective will be to integrate ML into accelerator operations and furthermore, provide an accessible framework, which can also be used by a broad range of other accelerator systems with dynamic tuning needs.

43 PARTICLE ACCELERATORS↗

DOE OSTI2022

Wall plug efficiency analysis of a compact SRF industrial accelerator [Poster]

Superconducting radiofrequency cavities offer extremely high (>90%) RF-to-beam energy conversion efficiency. Recent breakthroughs in the Nb 3 Sn SRF cavity technology, successful demonstration of the conduction cooling technique, and the availability of high cooling capacity cryocoolers has made possible the use of SRF for industrial particle accelerators. However, the overall wall plug-to-beam efficiency of such an SRF accelerator can be limited by the wall plug-to-RF power efficiency of the RF source powering this accelerator. The present study quantifies the wall plug-to-beam efficiency of a conduction-cooled SRF accelerator considering several different choices of the RF power source. The study concludes that the wall plug efficiency of the accelerator is indeed limited by that of the power source.

43 PARTICLE ACCELERATORS↗

DOE OSTI2022

Wall plug efficiency analysis of a compact SRF industrial accelerator [Poster]

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

High-Power Targetry R&D for Next-Generation Accelerator Target Facilities

Beam-intercepting devices such as beam windows and particle-production targets are critical components of accelerator target facilities for High Energy Physics (HEP) experiments. The high-power, pulsed structure of the particle beams used for these experiments leads to thermal shock and high-cycle fatigue in addition to radiation damage resulting from the accumulated particle fluence. This can lead to degradation of the target system s mechanical and thermal properties; considerably reducing their lifetimes and presenting substantial challenges to reliable operation of multi-MW class facilities. Recently several major accelerator facilities have been forced to operate at reduced power levels due to target survivability concerns. Furthermore, at Fermilab it is planned to increase the neutrino production beam power up to 2.4 MW in coming years. Therefore, timely R&D on the irradiated behavior of target system materials is critical to efficient operation of accelerator facilities and full utilization of recent accelerator power upgrades for HEP research. This talk will begin with an overview of high-power targetry, and the significant challenges presented by beam power increases expected for future HEP experiments. We will then cover several past materials irradiation studies that have been completed by the High-Power Targetry R&D group at Fermilab and its collaborators on common accelerator and target materials such as graphite, beryllium, titanium, and tungsten. Finally, we will conclude with a discussion of two novel materials investigations under way within the group; high-entropy alloys for beam window applications, and electrospun nanofibers to serve as particle production targets.

43 PARTICLE ACCELERATORS↗

DOE OSTI2020

Accelerators for HEP: Challenges and R&D

Particle accelerators are arguably the most effective tools for the particle physics research. The physics needs continuously push us to invent novel ways to increase energy and improve performance of accelerators, reduce their cost and make them more power efficient. Here we briefly overview three main families of modern and future accelerators for HEP – high intensity accelerators for neutrino research, particle factories for the electro-weak physics and Higgs studies, and post-LHC energy frontier colliders – and discuss corresponding ongoing or planned accelerator R&D topics and objectives.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

A Scalable, High-Efficiency, Low-Energy-Spread Laser Wakefield Accelerator Using a Tri-Plateau Plasma Channel

The emergence of multi-petawatt laser facilities is expected to push forward the maximum energy gain that can be achieved in a single stage of a laser wakefield acceleration (LWFA) to tens of giga-electron volts, which begs the question—is it likely to impact particle physics by providing a truly compact particle collider? Colliders have very stringent requirements on beam energy, acceleration efficiency, and beam quality. In this article, we propose an LWFA scheme that can for the first time simultaneously achieve hitherto unrealized acceleration efficiency from the laser to the electron beam of >20% and a sub-1% energy spread using a stepwise plasma structure and a nonlinearly chirped laser pulse. Three-dimensional high-fidelity simulations show that the nonlinear chirp can effectively mitigate the laser waveform distortion and lengthen the acceleration distance. This, combined with an interstage rephasing process in the stepwise plasma, can triple the beam energy gain compared to that in a uniform plasma for a fixed laser energy, thereby dramatically increasing the efficiency. A dynamic beam loading effect can almost perfectly cancel the energy chirp that arises during the acceleration, leading to the sub-percent energy spread. This scheme is highly scalable and can be applied to petawatt LWFA scenarios. Scaling laws are obtained, which suggest that electron beams with parameters relevant for a Higgs factory could be reached with the proposed high-efficiency, low-energy-spread scheme.

43 PARTICLE ACCELERATORS↗

DOE OSTI2017

Electromagnetic Structure and Electron Acceleration in Shock–Shock Interaction

A shock–shock interaction is investigated by using a one-dimensional full particle-in-cell simulation. The simulation reproduces the collision of two symmetrical high Mach number quasi-perpendicular shocks. The basic structure of the shocks and ion dynamics is similar to that obtained by previous hybrid simulations. The new aspects obtained here are as follows. Electrons are already strongly accelerated before the two shocks collide through multiple reflection. The reflected electrons self-generate waves upstream between the two shocks before they collide. The waves far upstream are generated through the right-hand resonant instability with the anomalous Doppler effect. The waves generated near the shock are due to firehose instability and have much larger amplitudes than those due to the resonant instability. The high-energy electrons are efficiently scattered by the waves so that some of them gain large pitch angles. Those electrons can be easily reflected at the shock of the other side. The accelerated electrons form a power-law energy spectrum. Due to the accelerated electrons, the pressure of upstream electrons increases with time. This appears to cause the deceleration of the approaching shock speed. The accelerated electrons having sufficiently large Larmor radii are further accelerated through the similar mechanism working for ions when the two shocks are colliding.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

The Acceleration of Charged Particles at a Spherical Shock Moving through an Irregular Magnetic Field

We investigate the physics of charged-particle acceleration at spherical shocks moving into a uniform plasma containing a turbulent magnetic field with a uniform mean. This has applications to particle acceleration at astrophysical shocks, most notably, to supernovae blast waves. We numerically integrate the equations of motion of a large number of test protons moving under the influence of electric and magnetic fields determined from a kinematically defined plasma flow associated with a radially propagating blast wave. Distribution functions are determined from the positions and velocities of the protons. The unshocked plasma contains a magnetic field with a uniform mean and an irregular component having a Kolmogorov-like power spectrum. The field inside the blast wave is determined from Maxwell’s equations. The angle between the average magnetic field and unit normal to the shock varies with position along its surface. It is quasi-perpendicular to the unit normal near the sphere’s equator, and quasi-parallel to it near the poles. We find that the highest intensities of particles, accelerated by the shock, are at the poles of the blast wave. The particles “collect” at the poles as they approximately adhere to magnetic field lines that move poleward from their initial encounter with the shock at the equator, as the shock expands. The field lines at the poles have been connected to the shock the longest. We also find that the highest-energy protons are initially accelerated near the equator or near the quasi-perpendicular portion of the shock, where the acceleration is more rapid.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

The Acceleration of Energetic Particles at Coronal Shocks and Emergence of a Double Power-law Feature in Particle Energy Spectra

We present numerical modeling of particle acceleration at coronal shocks propagating through a streamer-like magnetic field by solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that the location on the shock where the high-energy particle intensity is the largest, depends on the energy of the particles and on time. The acceleration of particles to more than 100 MeV mainly occurs in the shock-streamer interaction region, due to perpendicular shock geometry and the trapping effect of closed magnetic fields. A comparison of the particle spectra to that in a radial magnetic field shows that the intensity at 100 MeV (200 MeV) is enhanced by more than one order (two orders) of magnitude. This indicates that the streamer-like magnetic field can be an important factor in producing large solar energetic particle events. We also show that the energy spectrum integrated over the simulation domain consists of two different power laws. Further analysis suggests that it may be a mixture of two distinct populations accelerated in the streamer and open field regions, where the acceleration rate differs substantially. Our calculations also show that the particle spectra are affected considerably by a number of parameters, such as the streamer tilt angle, particle spatial diffusion coefficient, and shock compression ratio. While the low-energy spectra agree well with standard diffusive shock acceleration theory, the break energy ranges from ~1 MeV to ~90 MeV and the high-energy spectra can extend to ~1 GeV with a slope of ~2–3.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2019

Determining the Dominant Acceleration Mechanism during Relativistic Magnetic Reconnection in Large-scale Systems

While a growing body of research indicates that relativistic magnetic reconnection is a prodigious source of particle acceleration in high-energy astrophysical systems, the dominant acceleration mechanism remains controversial. Using a combination of fully kinetic simulations and theoretical analysis, in this work we demonstrate that Fermi-type acceleration within the large-scale motional electric fields dominates over direct acceleration from non-ideal electric fields within small-scale diffusion regions. This result has profound implications for modeling particle acceleration in large-scale astrophysical problems, as it opens up the possibility of modeling the energetic spectra without resolving microscopic diffusion regions.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2000

Spatiotemporal processing of linear acceleration: primary afferent and central vestibular neuron responses

Spatiotemporal convergence and two-dimensional (2-D) neural tuning have been proposed as a major neural mechanism in the signal processing of linear acceleration. To examine this hypothesis, we studied the firing properties of primary otolith afferents and central otolith neurons that respond exclusively to horizontal linear accelerations of the head (0.16-10 Hz) in alert rhesus monkeys. Unlike primary afferents, the majority of central otolith neurons exhibited 2-D spatial tuning to linear acceleration. As a result, central otolith dynamics vary as a function of movement direction. During movement along the maximum sensitivity direction, the dynamics of all central otolith neurons differed significantly from those observed for the primary afferent population. Specifically at low frequencies (</=0.5 Hz), the firing rate of the majority of central otolith neurons peaked in phase with linear velocity, in contrast to primary afferents that peaked in phase with linear acceleration. At least three different groups of central response dynamics were described according to the properties observed for motion along the maximum sensitivity direction. "High-pass" neurons exhibited increasing gains and phase values as a function of frequency. "Flat" neurons were characterized by relatively flat gains and constant phase lags (approximately 20-55 degrees ). A few neurons ("low-pass") were characterized by decreasing gain and phase as a function of frequency. The response dynamics of central otolith neurons suggest that the approximately 90 degrees phase lags observed at low frequencies are not the result of a neural integration but rather the effect of nonminimum phase behavior, which could arise at least partly through spatiotemporal convergence. Neither afferent nor central otolith neurons discriminated between gravitational and inertial components of linear acceleration. Thus response sensitivity was indistinguishable during 0.5-Hz pitch oscillations and fore-aft movements. The fact that otolith-only central neurons with "high-pass" filter properties exhibit semicircular canal-like dynamics during head tilts might have important consequences for the conclusions of previous studies of sensory convergence and sensorimotor transformations in central vestibular neurons.

NASA Discipline Neuroscience↗