Strong Longitudinal Magnetic Field Research Articles

High-order magnetic resonance in the presence of strong longitudinal radio-frequency magnetic field based on atomic alignment states

High-order magnetic resonance in the presence of strong longitudinal radio-frequency magnetic field based on atomic alignment states

Characterizing the dynamical magnetosphere of the extremely slowly rotating magnetic O9.7 V star HD 54879 using rotational modulation of the Hα profile

AbstractThe magnetic field in the O9.7 V star HD 54879 has been monitored for almost a decade. Spectropolarimetric observations reveal a rather strong mean longitudinal magnetic field that varies with a period of about 7.41 years. Observations in the H line show a variation with the same period, while the H line shows only little variation. Assuming the periodic variation to be caused by a slow rotation and a dipolar magnetic field, we find a magnetic field strength of 2 kG at the magnetic poles. With the relatively low mass loss rate of year−1, this star is a case of extremely strong magnetic confinement. Both theoretical arguments and numerical simulations indicate the presence of an extended disk of increased gas density in the equatorial plane of the magnetic field, where gas from the line‐driven stellar wind is trapped. This disk is likely to be the origin of the observed H emission, which peaks together with the strongest line‐of‐sight magnetic field. The profile of the H line is resolved in several components and shows a remarkable variability with the rotation period.

Interaction of a tubular charged-particle beam with eigenwaves of a plasma solid-state cylinder located in strong longitudinal magnetic field

An electrodynamic system in which a magnetized tubular electron beam blows around a cylindrical solid-state plasma waveguide located coaxially in a longitudinal magnetic field is theoretically studied. It has been established, when quasi-stationary conditions are satisfied, hybrid bulk-surface or surface electromagnetic waves of helicon origin are excited in the waveguide. The waveguide eigenwaves are excited by the space-charge field of beam with matching of the longitudinal spectral components of electric field. It is noted that helicons and waves of their nature are formed in a conducting plasma medium in the assistance of an external magnetic field. It is shown the instability of coupled waves of the electrodynamic system is due to the Vavilov–Cherenkov effect.

Curved Jet Motion. I. Orbiting and Precessing Jets

Astrophysical jets are often observed as bent or curved structures. We also know that the different jet sources may be binary in nature, which may lead to a regular, periodic motion of the jet nozzle, an orbital motion, or precession. Here we present the results of 2D (M)HD simulations in order to investigate how a precessing or orbiting jet nozzle affects the propagation of a high-speed jet. We have performed a parameter study of systems with different precession angles, different orbital periods or separations, and different magnetic field strengths. We find that these kinds of nozzles lead to curved jet propagation, which is determined by the main parameters that define the jet nozzle. We find C-shaped jets from orbiting nozzles and S-shaped jets from precessing nozzles. Over a long time and long distances, the initially curved jet motion bores a broad channel into the ambient gas that is filled with high-speed jet material whose lateral motion is damped, however. A strong (longitudinal) magnetic field can damp the jet curvature that is enforced by either precession or orbital motion of the jet sources. We have investigated the force balance across the jet and ambient medium and found that the lateral magnetic pressure and gas pressure gradients are almost balanced, but that a lack of gas pressure on the concave side of the curvature is leading to the lateral motion. Magnetic tension does not play a significant role. Our results are obtained in code units, but we provide scaling relations such that our results may be applied to young stars, microquasars, symbiotic stars, or active galactic nuclei.

Searching strong ‘spin’-orbit coupled one-dimensional hole gas in strong magnetic fields

We show that a strong ‘spin’-orbit coupled one-dimensional hole gas is achievable via applying a strong magnetic field to the original two-fold degenerate (spin degeneracy) hole gas confined in a cylindrical Ge nanowire. Both strong longitudinal and strong transverse magnetic fields are feasible to achieve this goal. Based on quasi-degenerate perturbation calculations, we show the induced low-energy subband dispersion of the hole gas can be written as , a form exactly the same as that of the electron gas in the conduction band. Here the Pauli matrices σ z,x represent a pseudo spin (or ‘spin’), because the real spin degree of freedom has been split off from the subband dispersions by the strong magnetic field. Also, for a moderate nanowire radius R = 10 nm, the induced effective hole mass and the ‘spin’-orbit coupling α (0.35 ∼ 0.8 eV Å) have a small magnetic field dependence in the studied magnetic field interval 1 < B < 15 T, while the effective g-factor of the hole ‘spin’ only has a small magnetic field dependence in the large field region.

HD 144941: the most extreme helium-strong star

Since its discovery about 50 yr ago, HD 144941 has generally been classified as a peculiar member of the extreme helium (EHe) supergiant stars, a very rare class of low-mass hydrogen-deficient stars. We report the detection of a strong longitudinal magnetic field based on spectropolarimetry with FORS2 on the ESO VLT with surface-averaged longitudinal field strengths as large as −9 kG. This is further constrained by the detection of Zeeman splitting of spectral lines to a field strength of at least 15 kG, explaining the recent finding of surface spots for this star. The quantitative analysis of the stellar atmosphere based on a hybrid non-local thermodynamic equilibrium approach and new optical spectra yields an effective temperature of 22 000 ± 500 K, a logarithmic surface gravity of 4.20 ± 0.10, and a surface helium fraction of 0.950 ± 0.002 by number. While the metal abundances are about a factor of 10 sub-solar in absolute number, the metal-to-hydrogen ratios are typical of massive early-type stars, indicating that helium fallback in a weak, fractionated stellar wind in the presence of a magnetic field took place – the canonical mechanism for the formation of the helium-strong phenomenon. Both the spectroscopic and the Gaia EDR3 parallax imply HD 144941 to be a luminous massive star. Kinematically, we argue that HD 144941 has reached its high Galactic latitude as a runaway star. We conclude that instead of being a comparatively high-gravity low-mass EHe star, HD 144941 is by far the most extreme member of the magnetic massive helium-strong stars, with almost all atmospheric hydrogen substituted by helium.

Thermal Trigger for Solar Flares II: Effect of the Guide Magnetic Field

We investigate the effect of the thermal imbalance on the structural stability of the magnetohydrodynamic model of the preflare current layer (Ledentsov in Solar. Phys. 296, 74, 2021). The piecewise homogeneous model of the current layer is supplemented by a magnetic field longitudinal with respect to the direction of the current. It is shown that the presence of a weak longitudinal field does not change the previously calculated spatial period of the thermal instability in the most expected range of the parameters of the preflare current layer and, moreover, contributes to the formation of the instability. On the other hand, a strong longitudinal magnetic field contributes to the spatial stabilization of the current layer.

Surface effects in superconductors with corners

We review some recent results on the phenomenon of surface superconductivity in the framework of Ginzburg-Landau theory for extreme type-II materials. In particular, we focus on the response of the superconductor to a strong longitudinal magnetic field in the regime where superconductivity survives only along the boundary of the wire. We derive the energy and density asymptotics for samples with smooth cross section, up to curvature-dependent terms. Furthermore, we discuss the corrections in presence of corners at the boundary of the sample.

On MHD Oscillations of a Plasma Column of Finite Conductivity with a Jump of Parameters in the Near-Wall Region

In a straight-cylinder model in a strong longitudinal magnetic field, the MHD oscillations of a plasma of a finite conductivity are considered in a situation when there is no resonant surface in the plasma on which the component of the perturbation wave vector vanishes along the field. At high conductivity, there are large-scale oscillations with a radial wavelength on the order of the column radius, which in the entire volume differ little from those described by an ideal MHD. It is shown that with a jump in the density and electron temperature on a certain magnetic surface near the wall, another MHD mode may exist along with such oscillations due to the finite conductivity. In this mode, the perturbations are large-scale and almost ideal in most of the plasma volume, but small-scale in the radial coordinate and not ideal in the wall region.

Formation and time development of spark channel in strong magnetic field

The characteristics of the spark channel plasma formed in the external longitudinal magnetic field are studied experimentally. In experiment, the current-voltage, optical, and spectral characteristics of the discharge were measured and analyzed. Synchronization of the pulsed electric and magnetic fields was performed. The effect of the magnetic field on the radial expansion of the spark channel, the shock wave formation, as well as the changes in the balance of energy and temperature in the ionized plasma of the high-pressure gas discharge were analyzed. It was found out that, in the strong longitudinal magnetic field, the temperatures of electrons and ions in the spark channel (ne ∼ 1018 cm−3) become equal. The current density, the plasma channel conductivity of the spark channel, and the specific energy deposition into the discharge increased. The channel plasma parameters were analyzed as functions of the external magnetic field.

Possibility of obtaining hot plasma during the breakdown of high-pressure gases in strong magnetic fields

The hot plasma production during the high-pressure gas breakdown in the strong magnetic fields with a magnetic strength H of up 16·106 A/m was considered experimentally. The breakdown occured in a short gap as a result of interaction of the monoenergetic electron beam (ne ∼ 1018 m−3, energy is about several keVs) with dense plasma (n ∼ 6 · 1022 m−3). The breakdown leads to the formation of the magnetic trap (magnetic mirror), and the discharge plasma becomes heated due to the electron beam, electron cyclotron resonance, and Joule heating processes. The studies have shown that the use of the strong longitudinal magnetic fields results in an increase in the specific power, conductivity, and plasma temperature.

Longitudinal magnetic field generation during the early stage of relativistic electron beam-plasma interaction

A mechanism for longitudinal magnetic field (i.e., the magnetic field parallel to the beam propagation direction) generation during the transport of relativistic electron beams with large edge gradients, through a high density plasma, is explained using two-dimensional (2D) particle-in-cell simulations and analytical theory. A ring structure is first formed due to the unneutralized beam current in the edge. Later, the counter-propagation of plasma return currents in the radial direction is excited due to the induction of a defocusing azimuthal magnetic field in the inner parts of the ring structure, with a characteristic crossing length of the ring width. Finally, the filamentation of plasma radial return currents in the azimuthal direction develops and contributes to the generation of a strong longitudinal magnetic field, which is shown to have strength on the same order of the transverse magnetic fields.

Improvement of ion acceleration in radiation pressure acceleration regime by using an external strong magnetic field

AbstractTwo-dimensional particle-in-cell (PIC) simulations have been used to investigate the interaction between a laser pulse and a foil exposed to an external strong longitudinal magnetic field. Compared with that in the absence of the external magnetic field, the divergence of proton with the magnetic field in radiation pressure acceleration (RPA) regimes has improved remarkably due to the restriction of the electron transverse expansion. During the RPA process, the foil develops into a typical bubble-like shape resulting from the combined action of transversal ponderomotive force and instabilities. However, the foil prefers to be in a cone-like shape by using the magnetic field. The dependence of proton divergence on the strength of magnetic field has been studied, and an optimal magnetic field of nearly 60 kT is achieved in these simulations.

Faraday rotation in cesium nano-layers in strong magnetic fields

ABSTRACTWe show that the Faraday rotation (FR) in strong longitudinal magnetic fields is a convenient tool to study atomic transitions by using the line in a Cs vapour confined in a nanocell of thickness nm. We use strong magnetic fields ranging from 0.1 to 6 kG, in which Cs atomic transitions are split into a large number of components, and FR signals of spectral width of ∼ 50 MHz are frequency-resolved allowing the investigation of individual transitions. For magnetic fields of several kG, the hyperfine Paschen–Back regime is reached that is manifested by the presence in the spectrum of the eight FR components having the amplitudes of the same height and located with almost equidistant frequencies. A remarkable feature of FR spectrum is the proportionality of its amplitude to the probability of an atomic transition in a strong magnetic field. A theoretical model which agrees well with the experiment is developed.

Generation of runaway electrons during the initial stage of the T-10 tokamak plasma discharge

The formation of runaway electron beams in the initial stage of discharge is one of the characteristic features of fusion facilities with magnetic plasma confinement, such as tokamaks. They are generated due to the presence of the high electric fields and strong plasma-wall interaction in plasma. The runaway electrons produced during the breakdown stage also remain in the plasma in the quasistationary stage of the discharge. Studies carried out at the T-10 tokamak show that the electron energy and the heat flux density can reach 5–10 MeV and 1–3 GW/m2, respectively. Thus, the interaction with electrons causes erosion and damage to the limiter surface. In this article, the energy distribution of high-energy electrons formed in the initial stage of plasma discharge in the T-10 tokamak during the formation of runaway electron beams in a strong longitudinal magnetic field was studied. The effect of the plasma density and MHD perturbations on the generation and acceleration of runaway electrons was revealed. The energy distributions of runaway electrons were estimated for different stages of the plasma discharge development.

Energy characteristics of high-pressure gas breakdown in strong longitudinal magnetic fields

Investigations of the magnetic field influence on energy (power) released in discharge, the electronic temperature, particle concentration, and the radiation of plasma of the channel-arc stages has a practical focus. It was found that the magnetic field leads to an increase in current density, conductivity, and specific energy input and a decrease in the formation times of all stages of discharge development, transverse integral radiation, and channel expansion rate, and shifts in the maximum spectral density of radiation in the ultraviolet region with simultaneous generation of new spectral lines. The magnetic field decreases the rate of spark channel expansion and the loss of transverse radiation and increases the specific power, conductivity and temperature of the plasma at channel-arc stages, creating conditions for obtaining a hot plasma.

Experimental observation of Bethe strings

Almost a century ago, string states-complex bound states of magnetic excitations-were predicted to exist in one-dimensional quantum magnets. However, despite many theoretical studies, the experimental realization and identification of string states in a condensed-matter system have yet to be achieved. Here we use high-resolution terahertz spectroscopy to resolve string states in the antiferromagnetic Heisenberg-Ising chain SrCo2V2O8 in strong longitudinal magnetic fields. In the field-induced quantum-critical regime, we identify strings and fractional magnetic excitations that are accurately described by the Bethe ansatz. Close to quantum criticality, the string excitations govern the quantum spin dynamics, whereas the fractional excitations, which are dominant at low energies, reflect the antiferromagnetic quantum fluctuations. Today, Bethe's result is important not only in the field of quantum magnetism but also more broadly, including in the study of cold atoms and in string theory; hence, we anticipate that our work will shed light on the study of complex many-body systems in general.

Компрессионные течения плазмы в КСПУ при наличии сильного продольного магнитного поля

Компрессионные течения плазмы в КСПУ при наличии сильного продольного магнитного поля

Characterizing the magnetic field and spectral variability of the rigidly rotating magnetosphere star HD 345439

Abstract A team involved in the Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the Sloan Digital Sky Survey III programmes, recently announced the discovery of two rare rigidly rotating magnetosphere stars, HD 345439 and HD 23478. Near-infrared spectra of these objects revealed emission-line behaviour identical to that previously discovered in the helium-strong star σ Ori E, which has a strong magnetic field and rotates fast. A single spectropolarimetric observation of HD 345439 with the FOcal Reducer low dispersion Spectrograph (FORS 2) at the Very Large Telescope (VLT) in 2014 over 88 min indicated that HD 345439 may host a strong, rapidly varying magnetic field. In this work, we present the results of our spectropolarimetric monitoring of this star with FORS 2, which revealed the presence of a strong longitudinal magnetic field dominated by a dipolar component. The analysis of spectral variability indicates an opposite behaviour of He and Si lines, which is usually attributed to differences in the distribution of surface He and Si abundance spots.

B field in OB stars (BOB): The outstandingly strong magnetic field in the evolved He-strong star CPD −62° 2124

The origin and evolution of magnetism in OB stars is far from being well understood. With approximately 70 magnetic OB stars known, any new object with unusual characteristics may turn out to be a key piece of the puzzle. We report the detection of an exceptionally strong magnetic field in the He-strong B2IV star CPD-62 2124. Spectropolarimetric FORS2 and HARPSpol observations were analysed by two independent teams and procedures, concluding on a strong longitudinal magnetic field of approximately 5.2 kG. The quantitative characterisation of the stellar atmosphere yields an effective temperature of 23650$\pm$250 K, a surface gravity of 3.95$\pm$0.10 dex and a surface helium fraction of 0.35$\pm$0.02 by number. The metal composition is in agreement with the cosmic abundance standard, except for Mg, Si and S, which are slightly non-solar. The strong and broad ($\sim$300 km/s) disc-like emission displayed by the H$\alpha$ line suggests a centrifugal magnetosphere supported by the strong magnetic field. Our results imply that CPD-62 2124 is an early B-type star hosting one of the strongest magnetic fields discovered to date, and one of the most evolved He-strong stars known, with a fractional main-sequence lifetime of approximately 0.6.