SEARCH · Search NASA

Results for “MAGNETIC CONFINEMENT”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Theoretical analysis of key factors achieving reversed magnetic shear q-profiles sustained with lower hybrid waves on EAST

The phase space analysis technique is applied to provide new insights into the fully non-inductive lower hybrid current driven (LHCD) discharges on EAST (Garofalo et al 2017 Nucl. Fusion 57 076037). The analysis shows that there are bounded and unbounded topologies of lower hybrid (LH) waves in phase space. For typical parameters on EAST, the propagation domain for 4.6 GHz LH waves is bounded, while unbounded for 2.45 GHz LH waves and one of the conditions is recognized to be good for achieving an off-axis current profile driven by 4.6 GHz LH waves on EAST. The parametric analysis on the potential power deposition (PPD) region for those experiments demonstrates that the reversed magnetic shear dominates the wave behavior, and confines the LH power absorption to the far off-axis region as long as it occurs in the 4.6 GHz dominated LHCD discharge. GENRAY/CQL3D simulations also confirm this effect of reversed shear on the power absorption of 4.6 GHz waves. A bounded propagation domain and a positive feedback loop between magnetic shear reversal and off-axis LHCD profile could explain the LH-only-sustained strong reversed magnetic shear observed in experiments on multiple machines. In contrast, there is no such effect for 2.45 GHz waves on EAST since the PPD region is less sensitive to the change of reversed shear due to the unbounded propagation domain.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Hilbert-Space Fragmentation from Strict Confinement

In this work, we study one-dimensional spin-1/2 models in which strict confinement of Ising domain walls leads to the fragmentation of Hilbert space into exponentially many disconnected subspaces. Whereas most previous works emphasize dipole moment conservation as an essential ingredient for such fragmentation, we instead require two commuting U(1) conserved quantities associated with the total domain-wall number and the total magnetization. The latter arises naturally from the confinement of domain walls. Remarkably, while some connected components of the Hilbert space thermalize, others are integrable by Bethe ansatz. We further demonstrate how this Hilbert-space fragmentation pattern arises perturbatively in the confining limit of $\mathbb{Z}_2$ gauge theory coupled to fermionic matter, leading to a hierarchy of timescales for motion of the fermions. This model can be realized experimentally in two complementary settings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

All-electrical detection of spin dynamics in magnetic antidot lattices by the inverse spin Hall effect

The understanding of spin dynamics in laterally confined structures on sub-micron length scales has become a significant aspect of the development of novel magnetic storage technologies. Numerous ferromagnetic resonance measurements, optical characterization by Kerr microscopy and Brillouin light scattering spectroscopy and x-ray studies were carried out to detect the dynamics in patterned magnetic antidot lattices. Here, we investigate Oersted-field driven spin dynamics in rectangular Ni80Fe20/Pt antidot lattices with different lattice parameters by electrical means. When the system is driven to resonance, a dc voltage across the length of the sample is detected that changes its sign upon field reversal, which is in agreement with a rectification mechanism based on the inverse spin Hall effect. Furthermore, we show that the voltage output scales linearly with the applied microwave drive in the investigated range of powers. Lastly, our findings have direct implications on the development of engineered magnonics applications and devices.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2026

Comparison of plasma response models for RMP effects on the divertor and scrape-off layer in KSTAR

Resonant magnetic perturbations (RMPs) are beneficial for control of edge localized modes (ELMs) in tokamaks. Nevertheless, a side effect of RMPs is the appearance of helical striations in the particle and heat loads onto divertor targets. The extent and field line connection of these striations is significantly altered by the plasma response to external perturbations. For an ELM suppressed high confinement (H-mode) plasma at KSTAR, magnetic footprints are computed by FLARE based on plasma response from GPEC, MARS-F, M3D-C1 and JOREK with substantial differences in the resulting footprints (from 2 cm to 14 cm). This is reflected in EMC3-EIRENE simulations of the resulting heat loads: it is found that either the peak value or the extent of the striations appears to be overestimated compared to infrared camera measurements. Reasonable agreement can only be achieved for the smallest footprint for lower input power and lower cross-field transport, or for higher upstream density and radiative power losses.

Frerichs, H. [Univ. of Wisconsin, Madison, WI (Uni↗

DOE OSTI2022

Confinement And Focusing

Iron-dominated room-temperature magnets remain the primary tool for steering and focusing beams of high energy particles. This article covers the electromagnetic and mechanical design of such magnets. It is a contribution to the third edition of the "Handbook of Accelerator Physics and Engineering" and a revision of FERMILAB-TM-2080.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Spin Vortex Resonance in Non-planar Ferromagnetic Dots

In planar structures, the vortex resonance frequency changes little as a function of an in-plane magnetic field as long as the vortex state persists. Altering the topography of the element leads to a vastly different dynamic response that arises due to the local vortex core confinement effect. In this work, we studied the magnetic excitations in non-planar ferromagnetic dots using a broadband microwave spectroscopy technique. Two distinct regimes of vortex gyration were detected depending on the vortex core position. The experimental results are in qualitative agreement with micromagnetic simulations.

36 MATERIALS SCIENCE↗

DOE OSTI2021

The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics

The Madison plasma dynamo experiment (MPDX) is a novel, versatile, basic plasma research device designed to investigate flow driven magnetohydrodynamic instabilities and other high-β phenomena with astrophysically relevant parameters. A 3 m diameter vacuum vessel is lined with 36 rings of alternately oriented 4000 G samarium cobalt magnets, which create an axisymmetric multicusp that contains ∼14 m3of nearly magnetic field free plasma that is well confined and highly ionized (>50%). At present, 8 lanthanum hexaboride (LaB6) cathodes and 10 molybdenum anodes are inserted into the vessel and biased up to 500 V, drawing 40 A each cathode, ionizing a low pressure Ar or He fill gas and heating it. Up to 100 kW of electron cyclotron heating power is planned for additional electron heating. The LaB6cathodes are positioned in the magnetized edge to drive toroidal rotation through J × B torques that propagate into the unmagnetized core plasma. Dynamo studies on MPDX require a high magnetic Reynolds number Rm > 1000, and an adjustable fluid Reynolds number 10 1). Initial results from MPDX are presented along with a 0-dimensional power and particle balance model to predict the viscosity and resistivity to achieve dynamo action.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Thermodynamics of energy magnetization

We construct the thermodynamics of energy magnetization in the presence of gravitomagnetic field. We show that the free energy must be modified to account for the modification of the energy current operator in the presence of a confining potential. The explicit expression of the energy magnetization is derived for a periodic system, and the Streda formula for the thermal Hall conductivity is rigorously established. Furthermore, we demonstrate our theory of the energy magnetization and the Streda formula in a Chern insulator.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Anticathode effect on electron kinetics in electron beam generated E × B plasma

Electron beam (e-beam) generated plasmas with applied crossed electric and magnetic (E x B) fields are promising for low damage processing of materials with applications to microelectronics and quantum information systems. In cylindrical e-beam E x B plasmas, radial confinement of electrons and ions is achieved by an axial magnetic field and radial electric field, respectively. To control the axial confinement of electrons, such e-beam generated plasma sources may incorporate a conducting boundary known as an anticathode, which is placed on the axially opposite side of the plasma from the cathode. In this work, it is shown that varying the anticathode voltage bias can control the degree to which the anticathode collects or repels incident electrons, allowing control of warm electron (electron energies in 10–30 eV range) and beam electron population confinement. It is suggested that the effect of the anticathode bias on the formation of these distinct electron populations is also associated with the transition between weak turbulence and strong Langmuir turbulence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2021

Integrability, normal forms, and magnetic axis coordinates

Integrable or near-integrable magnetic fields are prominent in the design of plasma confinement devices. Such a field is characterized by the existence of a singular foliation entirely consisting of invariant submanifolds. A compact regular leaf (a flux surface) of this foliation must be diffeomorphic to the two-torus. In a neighborhood of a flux surface, it is known that the magnetic field admits several exact smooth normal forms in which the field lines are straight. However, these normal forms break down near singular leaves, including elliptic and hyperbolic magnetic axes. In this work, the existence of exact smooth normal forms for integrable magnetic fields near elliptic and hyperbolic magnetic axes is established. In the elliptic case, smooth near-axis Hamada and Boozer coordinates are defined and constructed. Ultimately, these results establish previously conjectured smoothness properties for smooth solutions of the magnetohydrodynamic equilibrium equations. The key arguments are a consequence of a geometric reframing of integrability and magnetic fields: they are presymplectic systems.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2018

Mitigation of stimulated Raman scattering in the kinetic regime by external magnetic fields

Here, we show via particle-in-cell simulations that small normalized magnetic fields (ω c /ω p << 1) can significantly modify the evolution of backward stimulated Raman scattering (SRS) in the kinetic regime due to the enhanced dissipation of nonlinear electron plasma waves propagating perpendicular to magnetic fields. A magnetic field applied perpendicularly to the electron plasma wave (and driving light wave) increases the SRS threshold for kinetic inflation and decreases the amount of reflectivity when SRS is driven significantly above threshold. Analysis indicates that this arises because trapped electrons are accelerated as they surf across the wave, leading to the continual dissipation of the electron plasma waves over a wider range of wave amplitudes. The reduction in SRS reflectivity is most significant for a purely perpendicular field, although reduction also occurs for other angles; a parallel field can slightly increase single-speckle SRS but decreases multispeckle SRS. These simulations demonstrate the significance of magnetic-field contributions to nonlinear electron plasma wave damping with respect to nonlinear parametric decay instabilities; the simulation parameters are directly relevant for SRS in inertial confinement fusion devices and indicate that approximately 30 tesla magnetic fields might significantly reduce SRS backscatter.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2017

Effect of magnetic islands on profiles, flows, turbulence and transport in nonlinear gyrokinetic simulations

Neoclassical tearing modes have deleterious effects on plasma confinement and, if they grow large enough, they can lead to discharge termination. Therefore, they impose a major barrier in the development of operating scenarios of present-day tokamaks. Gyrokinetics offers a path toward studying multi-scale interactions with turbulence and the effect on plasma confinement. As a first step toward this goal, we have implemented static magnetic islands in nonlinear gyrokinetic simulations with the GENE code. We investigate the effect of the islands on profiles, flows, turbulence and transport and the scaling of these effects with respect to island size. We find a clear threshold island width, below which the islands have little or no effect while beyond this point the islands significantly perturb flows, increase turbulence and transport. Additionally, we study the effect of radially asymmetric islands on shear flows for the first time. We find that island induced shear flows can regulate turbulent fluctuation levels in the vicinity of the island separatrices. Throughout this work, we focus on experimentally relevant quantities, such as rms levels of density and electron temperature fluctuations, as well as amplitude and phasing of turbulence modulation. These simulations aim to provide guidelines for interpreting experimental results by comparing qualitative trends in the simulations with those obtained in tokamak experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

The muon g-2 experiment at Fermilab

The E989 collaboration has recently published the most precise measurement of the muon anomalous magnetic moment $a_\mu$ with an uncertainty of $0.46\,\mathrm{ppm}$. The new experimental world average of $a_\mu$ deviates by 4.2 standard deviations from the Standard Model prediction provided by the Muon g-2 Theory Initiative. Emerging results from ab-initio lattice QCD calculations for hadron-physics contributions allow to scrutinize this tantalizing hint for physics beyond the Standard Model for the first time in a three way comparison. To extract the value of $a_\mu$ a frequency comparison experiment is performed with spin-polarized muons confined in a superbly controlled electric and magnetic field environment. A measurement of the difference between the Larmor and the cyclotron frequency, the so-called anomalous spin precession frequency, is combined with a high-precision measurement of the magnetic field environment which is performed using nuclear magnetic resonance techniques. I discussed the most recent result of the Fermilab Muon g-2 experiment's first physics data run performed in 2018. I reported on the experimental improvements implemented for the subsequent science runs that will allow the collaboration to achieve the ultimate goal of $0.14\,\mathrm{ppm}$ uncertainty on $a_\mu$.

Fertl, Martin↗

DOE OSTI2019

Controlling spins with surface magnon polaritons

Polaritons in metals, semimetals, semiconductors, and polar insulators can allow for extreme confinement of electromagnetic energy, providing many promising opportunities for enhancing typically weak light-matter interactions such as multipolar radiation, multiphoton spontaneous emission, Raman scattering, and material nonlinearities. These extremely confined polaritons are quasielectrostatic in nature, with most of their energy residing in the electric field. As a result, these “electric” polaritons are far from optimized for enhancing emission of a magnetic nature, such as spin relaxation, which is typically many orders of magnitude slower than corresponding electric decays. Here, we take concepts of “electric” polaritons into magnetic materials, and propose using surface magnon polaritons in negative magnetic permeability materials to strongly enhance spin relaxation in nearby emitters. Specifically, we provide quantitative examples with MnF 2 and FeF 2 , enhancing spin transitions in the THz spectral range. In this work we find that these magnetic polaritons in 100-nm thin films can be confined to lengths over 10 000 times smaller than the wavelength of a photon at the same frequency, allowing for a surprising 12 orders of magnitude enhancement in magnetic dipole transitions. This takes THz spin-flip transitions, which normally occur at timescales on the order of a year, and forces them to occur at sub-ms timescales. Our results suggest an interesting platform for polaritonics at THz frequencies, and more broadly, a way to use polaritons to control light-matter interactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2026

Gate-Tunable Single Terahertz Meta-Atom Ultrastrong Light-Matter Coupling

We study the electrical tunability of ultrastrong light-matter interactions between a single terahertz circuit-based complementary split ring resonator (cSRR) and a two-dimensional electron gas. For this purpose, transmission spectroscopy measurements are performed under the influence of a strong magnetic field at different set points for the electric gate bias. The resulting Landau polariton dispersion depends on the applied electric bias, as the gating technique confines the electrons in-plane down to extremely subwavelength dimensions as small as d = 410 nm. This confinement allows for the excitation of standing plasma waves at zero magnetic field and an effective tunability of the electron number coupled to the THz resonator. This allows the normalized coupling strength to be tuned in situ from η = 0.46 down to η = 0.18. This is the first demonstration of terahertz far-field spectroscopy of an electrically tunable interaction between a single terahertz resonator and electrons in a GaAs quantum well heterostructure.

Landau levels↗

DOE OSTI2024

Heavy ion beam probe for Wendelstein 7-X measurement capabilities as projected through its design

A heavy ion beam probe (HIBP) diagnostic is being developed for studies of plasma equilibrium and turbulence in the optimized Wendelstein 7-X (W7-X) stellarator. Operation of W7-X has experimentally demonstrated that its optimized magnetic field results in improved neoclassical particle confinement and, as a result, turbulence is the predominant cause of energy transport. The HIBP will have the unique ability to provide experimental data needed to complement models of both neoclassical and turbulent transport. It will acquire direct measurements in the W7-X plasma interior of the electric potential (needed for understanding ambipolar particle flux) and fluctuations of electron density and potential (needed for understanding turbulence). The HIBP for W7-X will inject singly charged ion beams with energies of up to 2 MeV and is designed to access the upper cross section of the W7-X plasma. We use trajectory simulations to illustrate the plasma coverage that the diagnostic can achieve in the reference magnetic configurations of W7-X. We calculate beam signal levels, discuss anticipated measurement sensitivity of broadband fluctuations of electron density and plasma potential, and show how they depend on plasma density. We also discuss the diagnostic sensitivity to equilibrium plasma potential.

Instruments & Instrumentation↗

DOE OSTI2016

Observation of superconducting vortex clusters in S/F hybrids

While Abrikosov vortices repel each other and form a uniform vortex lattice in bulk type-II superconductors, strong confinement potential profoundly affects their spatial distribution eventually leading to vortex cluster formation. The confinement could be induced by the geometric boundaries in mesoscopic-size superconductors or by the spatial modulation of the magnetic field in superconductor/ ferromagnet (S/F) hybrids. Here we study the vortex confinement in S/F thin film heterostructures and we observe that vortex clusters appear near magnetization inhomogeneities in the ferromagnet, called bifurcations. We use magnetic force microscopy to image magnetic bifurcations and superconducting vortices, while high resolution scanning tunneling microscopy is used to obtain detailed information of the local electronic density of states outside and inside the vortex cluster. We find an intervortex spacing at the bifurcation shorter than the one predicted for the same superconductor in a uniform magnetic field equal to the thermodynamical upper critical field H c2 . This result is due to a local enhanced stray field and a competition between vortex-vortex repulsion and Lorentz force. Here, our findings suggest that special magnetic topologies could result in S/F hybrids that support superconductivity even when locally the vortex density exceeds the thermodynamic critical threshold value beyond which the superconductivity is destroyed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Suppression of type-I ELMs with reduced RMP coil set on DIII-D

Recent experiments on DIII-D have demonstrated that having a toroidally-monochromatic spectral content of edge-resonant magnetic perturbations (RMPs) is not a necessary condition for suppression of edge localized modes (ELMs). Robust ELM suppression has been reproducibly obtained on DIII-D during experiments in which various non-axisymmetric coil loops were turned off pseudo-randomly producing a variety of n=1 , n=2, and n=3 spectral contributions. It was demonstrated that RMP ELM suppression could be achieved with as few as 5 out of 12 internal coil loops (I-coils) on DIII-D at similar coil currents and with good plasma confinement. Linear MHD plasma response (M3DC1, IPEC, MARS) and vacuum (SURFMN, TRIP3D) modelling have been performed in order to understand the effects of the perturbation spectrum on the plasma response and ELM suppression. The results suggest that reduction of the dominant n=3 perturbation field is compensated by increased n=2 field in the plasma that may lead to RMP ELM suppression at lower levels of n=3 perturbative magnetic flux from the I-coils. In conclusion, these results provide additional confidence that ITER may be capable of RMP ELM suppression in the event of multiple internal coil failures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗