Plasma In Strong Magnetic Field Research Articles

D-Mag — a laboratory for studying plasma physics and diagnostics in strong magnetic fields

We have set up a diagnostic magnet (D-Mag) laboratory for a wide range of applications in plasma physics. It consists of a superconducting magnet for field strengths of up to 5.9 T. The main purpose is to provide an experimental environment for the development of plasma diagnostics for nuclear fusion studies and the investigation of dusty plasmas in strong magnetic fields. We describe in the article the setup and operation of the D-Mag. Some applications are presented for the development of plasma diagnostics, such as neutral pressure gauges and Langmuir probes that have to be operated in strong magnetic fields. Among the examples is the test of the long-pulse capability and stability of the diagnostic pressure gauge (DPG) for the ITER device.

Spectral analysis of the polarisation of drifting subpulses

Pulsars are among the most extreme objects in the Universe. Each one is born during a supernova – a dramatic explosion that happens when a bright star is many times bigger than our Sun and runs out of fuel. The heavy core of the star collapses under its own weight into something denser than the nucleus of an atom. Each pulsar has a magnetic field that is millions of times stronger than any that can be produced here on the Earth. Like a cosmic lighthouse, this magnetic field generates beams that sweep across the Galaxy with each rotation of the star (Gold, 1968); however, the underlying physics of the pulsar emission mechanism remains poorly understood after decades of study. Unlike the steady beam of a lighthouse, a pulsar's beam crackles and pops with lightning-like discharges of energy (Ruderman & Sutherland, 1975). By studying this highly dynamic signal, we learn about what generates the radio waves and what happens as they travel through the turbulent plasma in the pulsar's strong magnetic field. A relatively rare number of pulsars exhibit quasi-periodic variations in the polarization state of their emission (Primak et al., 2022). To provide new insight into the origin of this behaviour, I have developed a novel statistical method of studying quasi-periodic polarization fluctuations. I apply this technique to the first-discovered pulsar, and compare and contrast the results with previous work. The method can be applied to a wide range of radio pulsars and used to estimate the fraction of pulsars that exhibit quasi-periodic polarization fluctuations. In doing so, this experiment will provide new experimental constraints on theories of radio emission and propagation in the pulsar magnetosphere, and facilitate a deeper understanding of the physics of relativistic plasmas in strong magnetic fields.

Dynamic structure factor of the magnetized one-component plasma: Crossover from weak to strong coupling

Plasmas in strong magnetic fields have been mainly studied in two distinct limiting cases---that of weak and strong nonideality with very different physical properties. While the former is well described by the familiar theory of Braginskii, the latter regime is closer to the behavior of a Coulomb liquid. Here we study in detail the transition between both regimes. We focus on the evolution of the dynamic structure factor of the magnetized one-component plasma from weak to strong coupling, which is studied with first-principle molecular dynamics simulations. The simulations show the vanishing of Bernstein modes and the emergence of higher harmonics of the upper hybrid mode across the magnetic field, a redistribution of spectral power between the two main collective modes under oblique angles, and a suppression of plasmon damping along the magnetic field. Comparison with results from various models, including the random phase approximation, a Mermin-type dielectric function, and the quasilocalized charge approximation show that none of the theories is capable of reproducing the crossover that occurs when the coupling parameter is on the order of unity. The findings are relevant to the scattering spectra, stopping power, and transport coefficients of correlated magnetized plasmas.

Generation of strong magnetic fields for magnetized plasma experiments at the 1-MA pulsed power machine

Pulsed power technology provides a platform for investigating plasmas in strong magnetic fields using a university-scale machine. Presented here are methods for generating and measuring the 1–4-MG magnetic fields developed for the 1-MA Zebra pulsed power generator at the University of Nevada, Reno. A laser coupled with the Zebra generator produces a magnetized plasma, and experiments investigate how a megagauss magnetic field affects the two-plasmon decay and the expansion of the laser-produced plasma in both transverse and longitudinal magnetic fields.

Magnetic trap formation during the breakdown of high pressure gases in strong magnetic fields

Formation of hot plasma in strong magnetic fields during the breakdown of high-pressure gases in short gaps was studied experimentally. The breakdown occurs as a result of interaction of monoenergetic electron beam with dense plasma (n ∼ 6·1022 m−3). As a result of the spark channel formation and its explosive expansion inside the gap, the magnetic field in the anode and cathode regions becomes more intense, while between the electrodes it becomes weaker due to the expansion of the channel plasma. Thus, the axially symmetrical magnetic-mirror-type system is formed, which is similar to the magnetic trap. Formation of this system leads to the reduction of energy losses accompanied by a simultaneous increase in the plasma thermal energy, that is, to a considerable increase in its conductivity and temperature.

Diffusion coefficient for electrons in magnetized ultracold plasmas

The diffusion coefficients for electrons in an ultracold plasma in strong magnetic field were calculated for the first time by the molecular dynamics method. Earlier, we reported our results on the diffusion coefficients without magnetic field and obtained good agreement with experiment. In contrast to a convenient low-temperature plasma, strong magnetic field affects transport coefficients in an ultracold plasma event for field magnitudes 103–104 G. In the present paper a model of a system of charged particles consisting of electrons and protons interacting according to the Coulomb law without any correction of the potential at large or small distances was considered. Density of particles was varied from 1010 to 1012 cm−3; the initial temperature of the electrons was from 5 to 100 K, the temperature of the ions was from 10−3 to 2 K; induction of the magnetic field was from 0 to 5×104 G.

Bulk viscosity of quark-gluon plasma in strong magnetic fields

We investigate the viscosities of the quark-gluon plasma in strong magnetic fields within the leading-log and lowest Landau level (LLL) approximations. We first show that the bulk viscosity in the direction parallel to the magnetic field is the only component that has a contribution from the quarks occupying the LLL. We then compute the bulk viscosity from the Kubo formula and find an intriguing quark-mass dependence as a consequence of a competition between the suppression of the bulk viscosity by conformal symmetry and an enhancement of the mean-free path by chirality conservation, which governs the behavior in the massless limit. The quark contribution to the viscosity along the magnetic field becomes larger than the one in the absence of a magnetic field. We also briefly estimate the other transport coefficients by considering the contribution of gluons. We show that the shear viscosities are suppressed compared to their values in the absence of a magnetic field.

A Drift-Asymptotic scheme for a fluid description of plasmas in strong magnetic fields

We present a numerical scheme for the ion Euler equations with Braginskii closure, in the quasi-neutral regime with an adiabatic electron response. The scheme is constructed with the aid of asymptotic-preserving (AP) techniques in order to avoid the singularity in the drift-limit. When the normalized gyro-radius tends to zero, the scheme performs the drift-limit numerically. Depending on the choice of the time step, it can resolve different physical phenomena, ranging from cyclotron motion to plasma transport or ion drifts. Since the development of AP-schemes for the Braginskii equations is in its exploratory phase, the plasma is assumed a three-dimensional slab in a uniform external magnetic field. We use the ion-temperature-gradient dispersion relation for the scheme’s verification. The promising results show that the method offers the possibility to adapt the numerical parameters to the desired resolution in the full fluid model, instead of switching to reduced models in the drift-limit.

Electrical conductivity of quark-gluon plasma in strong magnetic fields

We compute the electrical conductivity of quark-gluon plasma in a strong magnetic field $B$ with quantum field theory at finite temperature using the lowest Landau level approximation. We provide the one-loop result arising from 1-to-2 scattering processes whose kinematics are satisfied by the (1+1) dimensional fermion dispersion relation. Due to the chirality conservation, the conductivity diverges in the massless limit, and is sensitive to the value of the current quark mass. As a result, we find that the conductivity along the direction of the magnetic field is quite large compared with the value at $B=0$, mainly because of the small value of the current quark mass. We show that the resummation of the ladder diagrams for the current-current correlator gives rise to only sub-leading contributions beyond the leading-log order, and thus verify our one-loop result at the leading-log accuracy. We also discuss possible implications for the relativistic heavy-ion collisions.

Energy loss of a nonaccelerating quark moving through a strongly coupledN=4super Yang-Mills vacuum or plasma in strong magnetic field

Using AdS/CFT correspondence, we find that a massless quark moving at the speed of light $v=1$, in arbitrary direction, through a strongly coupled $\mathcal{N}=4$ super Yang-Mills (SYM) vacuum at $T=0$, in the presence of strong magnetic field $\mathcal{B}$, loses its energy at a rate linearly dependent on $\mathcal{B}$, i.e., $\frac{dE}{dt}=-\frac{\sqrt{\lambda}}{6\pi}\mathcal{B}$. We also show that a heavy quark of mass $M\neq 0$ moving at near the speed of light $v^2=v_{*}^2=1-\frac{4\pi^2 T^2}{\mathcal{B}}\simeq1$, in arbitrary direction, through a strongly coupled $\mathcal{N}=4$ SYM plasma at finite temperature $T\neq 0$, in the presence of strong magnetic field $\mathcal{B}\gg T^2$, loses its energy at a rate linearly dependent on $\mathcal{B}$, i.e., $\frac{dE}{dt}=-\frac{\sqrt{\lambda}}{6\pi}\mathcal{B}v_{*}^2\simeq-\frac{\sqrt{\lambda}}{6\pi}\mathcal{B}$. Moreover, we argue that, in the strong magnetic field $\mathcal{B}\gg T^2$ (IR) regime, $\mathcal{N}=4$ SYM and adjoint QCD theories (when the adjoint QCD theory has four flavors of Weyl fermions and is at its conformal IR fixed point $\lambda=\lambda^*$) have the same microscopic degrees of freedom (i.e., gluons and lowest Landau levels of Weyl fermions) even though they have quite different microscopic degrees of freedom in the UV when we consider higher Landau levels. Therefore, in the strong magnetic field $\mathcal{B}\gg T^2$ (IR) regime, the thermodynamic and hydrodynamic properties of $\mathcal{N}=4$ SYM and adjoint QCD plasmas, as well as the rates of energy loss of a quark moving through the plasmas, should be the same.

16pCP-3 レーザー生成強磁場下での高エネルギー密度プラズマの流体運動に関するシミュレーションと実験結果の比較

16pCP-3 レーザー生成強磁場下での高エネルギー密度プラズマの流体運動に関するシミュレーションと実験結果の比較

Perpendicular currents and electric fields in fully and partially ionized magnetized plasma

Perpendicular currents and self-consistent electric fields in fully and partially ionized plasma in strong magnetic field are analyzed. In fully ionized plasma, the analyses are concentrated on closing of viscosity driven currents. For partially ionized plasma, it is demonstrated that the perpendicular currents could be expressed through the total pressure gradient (including the pressure gradient of neutral particles) and viscosity of neutrals. The self-consistent electric fields and corresponding E→×B→ could be quite large, which is important for various applications, in particular, for the divertor plasma of a tokamak in the detached regime.

Enhanced thermal photon and dilepton production in strongly coupled $ \mathcal{N} $ = 4 SYM plasma in strong magnetic field

We calculate the DC conductivity tensor of strongly coupled N=4 super-Yang-Mills (SYM) plasma in a presence of a strong external magnetic field B>>T^2 by using its gravity dual and employing both the RG flow approach and membrane paradigm which give the same results. We find that, since the magnetic field B induces anisotropy in the plasma, different components of the DC conductivity tensor have different magnitudes depending on whether its components are in the direction of the magnetic field B. In particular, we find that a component of the DC conductivity tensor in the direction of the magnetic field B increases linearly with B while the other components (which are not in the direction of the magnetic field B) are independent of it. These results are consistent with the lattice computations of the DC conductivity tensor of the QCD plasma in an external magnetic field B. Using the DC conductivity tensor, we calculate the soft or low-frequency thermal photon and dilepton production rates of the strongly coupled N=4 SYM plasma in the presence of the strong external magnetic field B>>T^2. We find that the strong magnetic field B enhances both the thermal photon and dilepton production rates of the strongly coupled N=4 SYM plasma in a qualitative agreement with the experimentally observed enhancements at the heavy-ion collision experiments.

Electromagnetic radiation by quark-gluon plasma in a magnetic field

The electromagnetic radiation by quark-gluon plasma in strong magnetic field is calculated. The contributing processes are synchrotron radiation and one--photon annihilation. It is shown that in relativistic heavy--ion collisions at RHIC and LHC synchrotron radiation dominates over the annihilation. Moreover, it constitutes a significant part of all photons produced by the plasma at low transverse momenta; its magnitude depends on the plasma temperature and the magnetic field strength. Electromagnetic radiation in magnetic field is probably the missing piece that resolves a discrepancy between the theoretical models and the experimental data. It is argued that electromagnetic radiation increases with the magnetic field strength and plasma temperature.

Models of magnetized neutron star atmospheres

We present a new computer code for modeling magnetized neutron star atmospheres in a wide range of magnetic fields ( 10 12 – 10 15 G ) and effective temperatures ( 3 × 10 5 – 10 7 K ) . The atmosphere is assumed to consist either of fully ionized electron-ion plasmas or of partially ionized hydrogen. Vacuum resonance and partial mode conversion are taken into account. Any inclination of the magnetic field relative to the stellar surface is allowed. We use modern opacities of fully or partially ionized plasmas in strong magnetic fields and solve the coupled radiative transfer equations for the normal electromagnetic modes in the plasma. Using this code, we study the possibilities to explain the soft X-ray spectra of isolated neutron stars by different atmosphere models. In particular, the outgoing spectrum using the “sandwich” model (thin atmosphere with a hydrogen layer above a helium layer) is constructed. Thin partially ionized hydrogen atmospheres with vacuum polarization are shown to be able to improve our understanding of the observed spectrum of the nearby isolated neutron star RBS 1223 (RX J1308.8+2127).

Models of magnetized neutron star atmospheres: thin atmospheres and partially ionized hydrogen atmospheres with vacuum polarization

Context. Observed X-ray spectra of some isolated magnetized neutron stars display absorption features, sometimes interpreted as ion cyclotron lines. Modeling the observed spectra is necessary to check this hypothesis and to evaluate neutron star parameters. Aims. We develop a computer code for modeling magnetized neutron star atmospheres in a wide range of magnetic fields (10 12 −10 15 G) and effective temperatures (3 × 10 5 −10 7 K). Using this code, we study the possibilities to explain the soft X-ray spectra of isolated neutron stars by different atmosphere models. Methods. The atmosphere is assumed to consist either of fully ionized electron-ion plasmas or of partially ionized hydrogen. Vacuum resonance and partial mode conversion are taken into account. Any inclination of the magnetic field relative to the stellar surface is allowed. We use modern opacities of fully or partially ionized plasmas in strong magnetic fields and solve the coupled radiative transfer equations for the normal electromagnetic modes in the plasma. Results. Spectra of outgoing radiation are calculated for various atmosphere models: fully ionized semi-infinite atmosphere, thin atmosphere, partially ionized hydrogen atmosphere, or novel “sandwich” atmosphere (thin atmosphere with a hydrogen layer above a helium layer). Possibilities of applications of these results are discussed. In particular, the outgoing spectrum using the “sandwich” model is constructed. Thin partially ionized hydrogen atmospheres with vacuum polarization are shown to be able to improve the fit to the observed spectrum of the nearby isolated neutron star RBS 1223 (RX J1308.8+2127).

MHD stationary symmetric flows with Hall effect

Stationary magnetohydrodynamic (MHD) flows with a symmetry are analyzed for very-low-density plasmas in strong magnetic fields, in the infinite conductivity limit. In this particular case the simplified form of Ohm's law usually employed in the ideal MHD case is no longer valid, because Hall's and electron pressure terms in the generalized Ohm's law must be retained. Thus we include them in our equations. The assumption of symmetry makes possible the definition of an ignorable coordinate and of current functions for the divergence free magnitudes. In the case without Hall's effect and electron pressure terms in Ohm's law, there is only one independent current function; in the present case, instead, two Stokes functions are independent. We choose the current function of the magnetic induction field and that of the plasma flux, $\psi$ and $\chi$ , to be independent. Then we can express the other Stokes functions of our problem as functions of $\psi$ and $\chi$ . We assume helical symmetry, as it is the most general form of spatial symmetry and impose incompressibility, that is ${\bf v\cdot\nabla\rho =}\,0$ . We obtain a system of two differential equations for $\psi$ and $\chi$ , and solve them for the particular case of constant density. Then we calculate the limit of our solution for Hall's effect that tends to zero, in order to make a comparison with the results obtained for the case without Hall's effect. Finally, we find the necessary conditions to obtain confined plasma columns embedded in a force-free plasma or in a vacuum.

Effects of Ion Bombardment on Carbon Nanotube Formation in Strongly Magnetized Glow-Discharge Plasmas

The effects of ion bombardment on the formation of multi-walled carbon nanotubes (MWNTs) are investigated by controlling radio-frequency (rf) glow-discharge plasmas in strong magnetic fields. When a magnetic field is weak (0.03 T), the MWNTs growing directly on an rf electrode are deformed by the bombardment of the high-energy ions generated by a large sheath electric field in front of the rf electrode. On the other hand, when a strong magnetic field (2 T) is applied, the MWNTs are observed to be well aligned and not to be deformed even under the condition that the rf electrode is negatively biased. These results can be explained by the fact that the ion bombardment energy is reduced despite the existence of the large sheath electric field, which is caused by the magnetization of the ions in the strong magnetic field.

Electroweak interactions between intense neutrino beams and dense electron-positron magnetoplasmas

The electroweak coupling between intense neutrino beams and strongly degenerate relativistic dense electron-positron magnetoplasmas is considered. The intense neutrino bursts interact with the plasma due to the weak Fermi interaction force, and their dynamics is governed by a kinetic equation. Our objective here is to develop a kinetic equation for a degenerate neutrino gas and to use that equation to derive relativistic magnetohydrodynamic equations. The latter are useful for studying numerous collective processes when intense neutrino beams nonlinearly interact with degenerate, relativistic, dense electron-positron plasmas in strong magnetic fields. If the number densities of the plasma particles are of the order of 1033 cm-3, the pair plasma becomes ultra-relativistic, which strongly affects the potential energy of the weak Fermi interaction. The new system of equations allows several neutrino-driven streaming instabilities involving new types of relativistic Alfven-like waves. The relevance of our investigation to the early universe and supernova explosions is discussed.

Erratum: Partially ionized hydrogen plasma in strong magnetic fields [Phys. Rev. E60, 2193 (1999)

Received 2 September 2000DOI:https://doi.org/10.1103/PhysRevE.63.019901©2000 American Physical Society