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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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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A 1.2 T canted cos $θ$ dipole magnet using high-temperature superconducting CORC ® wires

In this study, REBa 2 Cu 3 O x (REBCO, RE = rare earth elements) coated conductors can carry high current in high background fields, in principle enabling dipole magnetic fields beyond 20 T. Although model accelerator magnets wound with single REBCO tapes have been successfully demonstrated, magnet technology based on high-current REBCO cables for high-field accelerator magnet applications has yet to be established. We developed a two-layer canted cosθ dipole magnet with an aperture of 70 mm using 30 m long commercial Conductor on Round Core (CORC ® ) wires. The 3.1 mm diameter CORC ® wire contained 16 commercial REBCO tapes with a 30 $μ$m thick substrate. The magnet was tested at 77 and 4.2 K. It generated a peak dipole field of 1.2 T with 4.8 kA at 4.2 K with neither thermal runaway nor training. Reasonable geometric field quality and strong magnetization-current effects with multipole decay were observed. Our work demonstrated a feasible high-temperature superconducting magnet technology as a first step toward a new accelerator magnet paradigm that will enable high-field inserts for next-generation circular colliders and stand-alone magnets that can operate over a wide temperature range for a broad range of applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Electron acceleration by magnetic islands in a dynamically evolved coronal current sheet

This work simulated the electron acceleration by magnetic islands in a drastically evolved solar coronal current sheet via the combined 2.5-dimensional (2.5D) resistive Magnetohydrodynamics (MHD) and guiding-center approximation test-particle methods. With high magnetic Reynolds number of 105, the long–thin current sheet is evolved into a chain of magnetic islands, growing in size and coalescing with each other, due to tearing instability. The acceleration of electrons is studied in one typical phase when several large magnetic islands are formed. The results show that the electrons with an initial Maxwell distribution evolve into a heavy-tailed distribution and more than 20% of the electrons can be accelerated higher than 200 keV within 0.1 second and some of them can even be energized up to MeV ranges. The most energetic electrons have a tendency to be around the outer regions of the magnetic islands or to be located in the small secondary magnetic islands. We find that the acceleration and spatial distributions of the energetic electrons is caused by the trapping effect of the magnetic islands and the distributions of the parallel electric field E{sub p}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Towards 20 T Hybrid Accelerator Dipole Magnets

We report the most effective way to achieve very high collision energies in a circular particle accelerator is to maximize the field strength of the main bending dipoles. In dipole magnets using Nb-Ti superconductor the practical field limit is considered to be 8-9 T. When Nb 3 Sn superconductor material is utilized, a field level of 15-16 T can be achieved. To further push the magnetic field beyond the Nb 3 Sn limits, High Temperature Superconductors (HTS) need to be considered in the magnet design. The most promising HTS materials for particle accelerator magnets are Bi2212 and REBCO. However, their outstanding performance comes with a significantly higher cost. Therefore, an economically viable option towards 20 T dipole magnets could consist in an “hybrid” solution, where both HTS and Nb3Sn materials are used. We discuss in this paper preliminary conceptual designs of various 20 T hybrid magnet concepts. After the definition of the overall design criteria, the coil dimensions and parameters are investigated with finite element models based on simple sector coils. Preliminary 2D cross-section computation results are then presented and three main layouts compared: cos-theta, block, and common-coil. Both traditional designs and more advanced stress-management options are considered.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

A Quasi-static Hyper-resistive Model of Ultra-high-energy Cosmic-ray Acceleration by Magnetically Collimated Jets Created by Active Galactic Nuclei

This is the fourth in a series of companion papers showing that when an efficient dynamo can be maintained by accretion disks around supermassive black holes in active galactic nuclei, it will lead to the formation of a powerful, magnetically collimated helix that could explain the observed jet/radiolobe structures on very large scales. In this work, we present a hyper-resistive kinetic theory that shows how different instabilities can cause the slowly evolving magnetically collimated jets to accelerate ions and electrons in different regions of jets and lobes. In particular, we propose that the Drift Cyclotron Loss Cone instability at the ends of jets can accelerate ions up to the observed ultra-high-energy cosmic rays with energies ≈1020 eV. Based on this jet/lobe structure model and its associated acceleration processes, we estimate cosmic-ray intensities and likely radiative signatures and compare them with observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Superconducting magnets and technologies for future colliders

The implications of accelerator magnet R&D towards future colliders are reviewed and discussed. It starts with a brief overview of the present and future accelerator facilities which rely on the significant advances and innovations in key technologies. Then advances and needs for present key projects and studies are expanded on specific examples. This provides the lead to discuss the recent progress in accelerator magnet R&D and the future plans. We conclude with a summary of our view of the major development drivers and future perspectives.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Performance of a MQXF Nb 3 Sn Quadrupole Magnet Under Different Stress Level

In a dipole or in a quadrupole accelerator magnet, the displacement of the coil turns induced by the electromagnetic forces can cause quenches limiting the magnet performance. For this reason, an azimuthal preload is applied to avoid azimuthal movements of the coil up to the required operational current. However, several tests showed that accelerator magnets can operate with a partial preload, i.e. that coil unloading during the ramp does not prevent reaching higher currents. This issue is particularly relevant for Nb 3 Sn magnets, where the loads applied to the Nb3Sn filaments can reach the degradation limits of critical current. In order to investigate the impact of coil preload on the quench performance, the MQXFS6 short model quadrupole for the High Luminosity Upgrade was tested under an azimuthal preload at 80% of the short sample current, reaching 93% of short sample current at 1.9 K. The preload was then released to 60%, still showing ability to operate in the range of 80-85% of short sample current as required by HL-LHC project. With this lower preload, the ability of going above 90% of short sample was lost, and a significant training appeared above 85%. When the preload was restored to the original 80% value, the magnet reached with few quenches 95% of short sample (13.4 T peak field). Magnetic measurements confirm the larger movement of the coil in the case with lower preload, and agree with finite element simulations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Progress with high-field superconducting magnets for high-energy colliders

One of the possible next steps for high-energy physics research relies on a high-energy hadron or muon collider. The energy of a circular collider is limited by the strength of bending dipoles, and its maximum luminosity is determined by the strength of final focus quadrupoles. For this reason, the high-energy physics and accelerator communities have shown much interest in higher-field and higher-gradient superconducting accelerator magnets. The maximum field of NbTi magnets used in all present high-energy machines, including the LHC, is limited to ~10 T at 1.9 K. Fields above 10 T became possible with the use of Nb$_3$Sn superconductors. Nb$_3$Sn accelerator magnets can provide operating fields up to ~15 T and can significantly increase the coil temperature margin. Accelerator magnets with operating fields above 15 T require high-temperature superconductors. Furthermore, this review discusses the status and main results of Nb$_3$Sn accelerator magnet research and development and work toward 20-T magnets.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Accelerated nanoscale magnetic resonance imaging through phase multiplexing

We report a method for accelerated nanoscale nuclear magnetic resonance imaging by detecting several signals in parallel. Our technique relies on phase multiplexing, where the signals from different nuclear spin ensembles are encoded in the phase of an ultrasensitive magnetic detector. We demonstrate this technique by simultaneously acquiring statistically polarized spin signals from two different nuclear species ({sup 1}H, {sup 19}F) and from up to six spatial locations in a nanowire test sample using a magnetic resonance force microscope. We obtain one-dimensional imaging resolution better than 5 nm, and subnanometer positional accuracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

THE ROLE OF PRESSURE ANISOTROPY ON PARTICLE ACCELERATION DURING MAGNETIC RECONNECTION

Voyager spacecraft observations have revealed that contrary to expectations, the source of anomalous cosmic rays (ACRs) is not at the local termination shock. A possible mechanism of ACR acceleration is magnetic reconnection in the heliosheath. Using a particle-in-cell code, we investigate the effects of {beta} on reconnection-driven particle acceleration by studying island growth in multiple interacting Harris current sheets. Many islands are generated, and particles are dominantly heated through Fermi reflection in contracting islands during island growth and merging. There is a striking difference between the heating of electrons versus the heating of ions. There is a strong dependence of {beta} on electron heating, while the ion heating is insensitive to {beta}. Anisotropies develop with T {sub Parallel-To} {ne} T for both electrons and ions. The electron anisotropies support the development of a Weibel instability that suppresses the Fermi acceleration of the electrons. Since the Weibel instability develops at a larger T {sub Parallel-To }/T in lower {beta} systems, electrons are able to accelerate more efficiently by the Fermi mechanism at low {beta}. The variance in anisotropy implies less electron acceleration in higher {beta} systems, and thus less heating. This study sheds light on particle acceleration mechanisms within the sectored magnetic field regions of the heliosheath and the dissipation of turbulence such as that produced by the magnetorotational instability in accreting systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Accelerating the magnetic island by the modulated resonant magnetic perturbation for the disruption avoidance on J-TEXT

We report the acceleration of the magnetic island rotation by the modulated resonant magnetic perturbation (MRMP) has been studied in J-TEXT tokamak experiments. After applying the MRMP, the phase difference between the tearing mode (TM) and MRMP, Δξ, oscillated near the effective phase difference, Δξ eff , which was defined as the time averaged value of Δξ. When the Δξ eff was closed to the—π/2, the MRMP only contributed an accelerating torque on the TM. As the result, the TM rotation frequency was increased by a few kilohertz for the optimized relative phase by small RMPs of the order of 10 -5 of the toroidal field and the locked mode induced disruption was avoided. It is found that the TM rotation could be increased to a higher frequency by applying a stronger MRMP. There is a negative sinusoidal relationship between TM frequency and Δξ eff .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

High-Energy Ions from Near-Critical Density Plasmas via Magnetic Vortex Acceleration

Ultraintense laser pulses propagating in near-critical density plasmas generate magnetic dipole vortex structures. In the region of decreasing plasma density, the vortex expands both in forward and lateral directions. The magnetic field pressure pushes electrons and ions to form a density jump along the vortex axis and induces a longitudinal electric field. This structure moves together with the expanding dipole vortex. The background ions located ahead of the electric field are accelerated to high energies. The energy scaling of ions generated by this magnetic vortex acceleration mechanism is derived and corroborated using particle-in-cell simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

A viable dipole magnet concept with REBCO CORC ® wires and further development needs for high-field magnet applications

REBCO coated conductors maintain a high engineering current density above 16 T at 4.2 K. That fact will significantly impact markets of various magnet applications including high-field magnets for high-energy physics and fusion reactors. One of the main challenges for the high-field accelerator magnet is the use of multi-tape REBCO cables with high engineering current density in magnet development. Several approaches developing high-field accelerator magnets using REBCO cables are demonstrated. In this paper, we introduce an alternative concept based on the canted cos θ (CCT) magnet design using conductor on round core (CORC®) wires that are wound from multiple REBCO tapes with a Cu core. We report the development and test of double-layer three-turn CCT dipole magnets using CORC ® wires at 77 and 4.2 K. The scalability of the CCT design allowed us to effectively develop and demonstrate important magnet technology features such as coil design, winding, joints and testing with minimum conductor lengths. The test results showed that the CCT dipole magnet using CORC ® wires was a viable option in developing a REBCO accelerator magnet. One of the critical development needs is to increase the engineering current density of the 3.7 mm diameter CORC® wire to 540 A mm -2 at 21 T, 4.2 K and to reduce the bending radius to 15 mm. Furthermore, this would enable a compact REBCO dipole insert magnet to generate a 5 T field in a background field of 16 T at 4.2 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Plasma-based Accelerator with Magnetic Compression

Electron dephasing is a major gain-inhibiting effect in plasma-based accelerators. A novel method is proposed to overcome dephasing, in which the modulation of a modest (~$\mathcal{O}$(10 kG)), axial, uniform magnetic field in the acceleration channel leads to densification of the plasma through magnetic compression, enabling direct, time-resolved control of the plasma wave properties. The methodology is broadly applicable and can be optimized to improve the leading acceleration approaches, including plasma beat-wave, plasma wakefield, and laser wakefield acceleration. The advantages of magnetic compression compared to other proposed schemes to overcome dephasing are identified.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2016

Magnetospheric Multiscale Satellite Observations of Parallel Electron Acceleration in Magnetic Field Reconnection by Fermi Reflection from Time Domain Structures

The same time domain structures (TDS) have been observed on two Magnetospheric Multiscale Satellites near Earth's dayside magnetopause. These TDS, traveling away from the X line along the magnetic field at 4000 km/s, accelerated field-aligned approx. 5 eV electrons to approx. 200 eV by a single Fermi reflection of the electrons by these overtaking barriers. Additionally, the TDS contained both positive and negative potentials, so they were a mixture of electron holes and double layers. They evolve in approx.10 km of space or 7 ms of time and their spatial scale size is 10-20 km, which is much larger than the electron gyroradius (less than1km) or the electron inertial length (4 km at the observation point, less nearer the X line).

Mozer, F. S.↗
DOE OSTI2023

Non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma

Magnetic reconnection rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy and non-thermal energetic particles. Various reconnection acceleration mechanisms have been theoretically proposed and numerically studied in different collisionless and low-β environments, where β refers to the plasma-to-magnetic pressure ratio. These mechanisms include Fermi acceleration, betatron acceleration, parallel electric field acceleration along magnetic fields and direct acceleration by the reconnection electric field. However, none of them have been experimentally confirmed, as the direct observation of non-thermal particle acceleration in laboratory experiments has been difficult due to short Debye lengths for in situ measurements and short mean free paths for ex situ measurements. Here we report the direct measurement of accelerated non-thermal electrons from magnetically driven reconnection at low β in experiments using a laser-powered capacitor coil platform. We use kilojoule lasers to drive parallel currents to reconnect megagauss-level magnetic fields in a quasi-axisymmetric geometry. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that the mechanism of direct electric field acceleration by the out-of-plane reconnection electric field is at work. Scaled energies using this mechanism show direct relevance to astrophysical observations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Impact of compressibility and a guide field on Fermi acceleration during magnetic island coalescence

Previous work has shown that Fermi acceleration can be an effective heating mechanism during magnetic island coalescence, where electrons may undergo repeated reflections as the magnetic field lines contract. This energization has the potential to account for the power-law distributions of particle energy inferred from observations of solar flares. In this study, we develop a generalized framework for the analysis of Fermi acceleration that can incorporate the effects of compressibility and non-uniformity along field lines, which have commonly been neglected in previous treatments of the problem. Applying this framework to the simplified case of the uniform flux tube allows us to find both the power-law scaling of the distribution function and the rate at which the power-law behavior develops. We find that a guide magnetic field of order unity effectively suppresses the development of power-law distributions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Large-scale Compression Acceleration during Magnetic Reconnection in a Low- β Plasma

In solar flares and other astrophysical systems, a major challenge for solving the particle acceleration problem associated with magnetic reconnection is the enormous scale separation between kinetic scales and the observed reconnection scale. Because of this, it has been difficult to draw any definite conclusions by just using kinetic simulations. A particle acceleration model that solves the energetic particle transport equation can capture the main acceleration physics found in kinetic simulations and thus provide a practical way to make observable predictions and directly compare model results with observations. Here we study compression particle acceleration in magnetic reconnection by solving the Parker (diffusion–advection) transport equation using velocity and magnetic fields from two-dimensional magnetohydrodynamics (MHD) simulations of a low-β high-Lundquist-number reconnection layer. We show that the compressible reconnection layer can give significant particle acceleration, leading to the formation of power-law particle energy distributions. We analyze the acceleration rate and find that the acceleration in the reconnection layer is a mixture of first- and second-order Fermi processes. When including a guide field, we find that the spectrum becomes steeper and both the power-law cutoff energy and maximum particle energy decrease as plasma becomes less compressible. This model produces a 2D particle distribution that one can use to generate a radiation map and directly compare with solar flare observations. This provides a framework to explain particle acceleration at large-scale astrophysical reconnection sites, such as solar flares.

79 ASTRONOMY AND ASTROPHYSICS↗