scholarly journals Mirror mode physics: Amplitude limit

2019 ◽  
Author(s):  
Rudolf A. Treumann ◽  
Wolfgang Baumjohann
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Dominant Role ◽  
Sound Waves ◽  
Final State ◽  
Temperature Plasma ◽  
Electron Pairs ◽  
Mirror Mode ◽  
Spacecraft Data ◽  
The Magnetic Field

Abstract. The mirror mode evolving in collisionless magnetised high-temperature thermally anisotropic plasmas is shown to resemble a macro-quantum state. Starting as a classical zero frequency ion fluid instability it saturates quasi-linearly at very low magnetic level, while forming extended magnetic bubbles.It traps the electron component into an adiabatic bounce motion along the magnetic field which causes a bulk electron anisotropy. This can drive an electron mirror mode (see Treumann and Baumjohann, 2018b, who identified it in old spacecraft data). More important, however, we show that trapped electrons play the dominant role of further evolution towards a stationary state. Interaction of the trapped bouncing electrons with the thermal level of ion sound waves causes attractive potentials between electrons and forms electron pairs in the lowest-energy singlet state of two combined electrons. This happens preferentially near the electron mirror points resulting in a diamagnetic current effect which ultimately drives evolution of the magnetic field into large amplitude mirror bubbles causing diamagnetism and expelling a larger fraction of magnetic flux from the interior of the initial quasi-linearly stable mirror mode bottle. Estimates given in view of mirror modes in the magnetosheath are in reasonable numerical agreement with observation. We derive the self-consistent final state of the mirror bubbles. This analysis demonstrates that the observed mirror mode in high temperature space plasmas (solar wind, magnetosheath, magnetotail) is not a simple magnetohydrodynamic instability. It resembles a classical super-conducting, super-fluid state in high temperature plasma under conditions when electron pairs form. This is a most interesting observation which suggests that pair formation can become relevant in space and astrophysics.

scholarly journals The strange physics of low frequency mirror mode turbulence in the high temperature plasma of the magnetosheath

2004 ◽  
Vol 11 (5/6) ◽  
pp. 647-657 ◽  
Author(s):  
R. A. Treumann ◽  
C. H. Jaroschek ◽  
O. D. Constantinescu ◽  
R. Nakamura ◽  
O. A. Pokhotelov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Particle Density ◽  
Convective Transport ◽  
Magnetized Plasma ◽  
Temperature Plasma ◽  
High Temperature Plasma ◽  
Fluid Theory ◽  
Mirror Mode ◽  
The Magnetic Field

Abstract. Mirror mode turbulence is the lowest frequency perpendicular magnetic excitation in magnetized plasma proposed already about half a century ago by Rudakov and Sagdeev (1958) and Chandrasekhar et al. (1958) from fluid theory. Its experimental verification required a relatively long time. It was early recognized that mirror modes for being excited require a transverse pressure (or temperature) anisotropy. In principle mirror modes are some version of slow mode waves. Fluid theory, however, does not give a correct physical picture of the mirror mode. The linear infinitesimally small amplitude physics is described correctly only by including the full kinetic theory and is modified by existing spatial gradients of the plasma parameters which attribute a small finite frequency to the mode. In addition, the mode is propagating only very slowly in plasma such that convective transport is the main cause of flow in it. As the lowest frequency mode it can be expected that mirror modes serve as one of the dominant energy inputs into plasma. This is however true only when the mode grows to large amplitude leaving the linear stage. At such low frequencies, on the other hand, quasilinear theory does not apply as a valid saturation mechanism. Probably the dominant processes are related to the generation of gradients in the plasma which serve as the cause of drift modes thus transferring energy to shorter wavelength propagating waves of higher nonzero frequency. This kind of theory has not yet been developed as it has not yet been understood why mirror modes in spite of their slow growth rate usually are of very large amplitudes indeed of the order of |B/B0|2~O(1). It is thus highly reasonable to assume that mirror modes are instrumental for the development of stationary turbulence in high temperature plasma. Moreover, since the magnetic field in mirror turbulence forms extended though slightly oblique magnetic bottles, low parallel energy particles can be trapped in mirror modes and redistribute energy (cf. for instance, Chisham et al. 1998). Such trapped electrons excite banded whistler wave emission known under the name of lion roars and indicating that the mirror modes contain a trapped particle component while leading to the splitting of particle distributions (see Baumjohann et al., 1999) into trapped and passing particles. The most amazing fact about mirror modes is, however, that they evolve in the practically fully collisionless regime of high temperature plasma where it is on thermodynamic reasons entirely impossible to expel any magnetic field from the plasma. The fact that magnetic fields are indeed locally extracted makes mirror modes similar to "superconducting" structures in matter as known only at extremely low temperatures. Of course, microscopic quantum effects do not play a role in mirror modes. However, it seems that all mirror structures have typical scales of the order of the ion inertial length which implies that mirrors evolve in a regime where the transverse ion and electron motions decouple. In this case the Hall kinetics comes into play. We estimate that in the marginally stationary nonlinear state of the evolution of mirror modes the modes become stretched along the magnetic field with k||=0 and that a small number the order of a few percent of the particle density is responsible only for the screening of the field from the interior of the mirror bubbles.

scholarly journals Electron pairing in mirror modes: surpassing the quasi-linear limit

2019 ◽  
Vol 37 (5) ◽  
pp. 971-988 ◽  
Author(s):  
Rudolf A. Treumann ◽  
Wolfgang Baumjohann
Keyword(s):  
High Temperature ◽  
Sound Waves ◽  
Pressure Balance ◽  
Final State ◽  
Temperature Plasma ◽  
Growth Pressure ◽  
First Case ◽  
Fluid Instability ◽  
Linear Limit ◽  
Mirror Mode

Abstract. The mirror mode evolving in collisionless magnetised high-temperature thermally anisotropic plasmas is shown to develop an interesting macro-state. Starting as a classical zero-frequency ion fluid instability it saturates quasi-linearly at very low magnetic level, while forming elongated magnetic bubbles which trap the electron component to perform an adiabatic bounce motion along the magnetic field. Further evolution of the mirror mode towards a stationary state is determined by the bouncing trapped electrons which interact with the thermal level of ion sound waves and generate attractive wake potentials which give rise to the formation of electron pairs in the lowest-energy singlet state of two combined electrons. Pairing preferentially takes place near the bounce-mirror points where the pairs become spatially locked with all their energy in the gyration. The resulting large anisotropy of pairs enters the mirror growth rate in the quasi-linearly stable mirror mode. It breaks the quasi-linear stability and causes further growth. Pressure balance is either restored by dissipation of the pairs and their anisotropy or inflow of plasma from the environment. In the first case new pairs will continuously form until equilibrium is reached. In the final state the fraction of pairs can be estimated. This process is open to experimental verification. To our knowledge it is the only process in which high-temperature plasma pairing may occur and has an important observable macroscopic effect: breaking the quasi-linear limit and, via pressure balance, generation of localised diamagnetism.

Plasma containment and stability theory

1968 ◽  
Vol 304 (1478) ◽  
pp. 335-360 ◽  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Low Frequency ◽  
Equilibrium Distribution Function ◽  
Temperature Plasma ◽  
Loss Cone ◽  
Magnetic Traps ◽  
Drift Wave ◽  
The Magnetic Field

Models of the behaviour of high temperature plasma are applied to the problem of plasma confinement in magnetic traps. A wide variety of possible instabilities is disclosed. In magnetic mirror traps the low frequency instabilties can be overcome by design of the magnetic field. The high frequency instabilities, particularly those associated with the loss-cone character of the equilibrium distribution function, are more persistent and appear to impose severe restrictions on the dimensions of the plasma. Consequently toroidal traps seem to offer a better prospect for long-term containment but at present they are subject to low frequency instabilities which persist even when conditions for hydromagnetic stability have been met. These instabilities may be due to small resistive effects or to an unstable drift wave. The resistive instabilities should disappear at high temperature and the drift-wave in­stability should be overcome by increased shear in the magnetic field.

scholarly journals Destruction of localized electron pairs above the magnetic-field-driven superconductor-insulator transition in amorphous In-O films

JETP Letters ◽  
1998 ◽  
Vol 68 (4) ◽  
pp. 363-369 ◽  
Author(s):  
V. F. Gantmakher ◽  
M. V. Golubkov ◽  
V. T. Dolgopolov ◽  
G. E. Tsydynzhapov ◽  
A. A. Shashkin
Keyword(s):  
Magnetic Field ◽  
Insulator Transition ◽  
Electron Pairs ◽  
The Magnetic Field ◽  
Superconductor Insulator Transition

The activation energy U(T,B) in high temperature superconductor

2020 ◽  
Vol 92 (2) ◽  
pp. 20601
Author(s):  
Abdelaziz Labrag ◽  
Mustapha Bghour ◽  
Ahmed Abou El Hassan ◽  
Habiba El Hamidi ◽  
Ahmed Taoufik ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Activation Energy ◽  
Phase Diagram ◽  
High Temperature ◽  
Apparent Activation Energy ◽  
High Temperature Superconductor ◽  
Flux Flow ◽  
Resistivity Measurements ◽  
Vortex Phase ◽  
The Magnetic Field

It is reported in this paper on the thermally assisted flux flow in epitaxial YBa2Cu3O7-δ deposited by Laser ablation method on the SrTiO3 substrate. The resistivity measurements ρ (T, B) of the sample under various values of the magnetic field up to 14T in directions B∥ab-plane and B∥c-axis with a dc weak transport current density were investigated in order to determine the activation energy and then understand the vortex dynamic phenomena and therefore deduce the vortex phase diagram of this material. The apparent activation energy U0 (B) calculated using an Arrhenius relation. The measured results of the resistivity were then adjusted to the modified thermally assisted flux flow model in order to account for the temperature-field dependence of the activation energy U (T, B). The obtained values from the thermally assisted activation energy, exhibit a behavior similar to the one showed with the Arrhenius model, albeit larger than the apparent activation energy with ∼1.5 order on magnitude for both cases of the magnetic field directions. The vortex glass model was also used to obtain the vortex-glass transition temperature from the linear fitting of [d ln ρ/dT ] −1 plots. In the course of this work thanks to the resistivity measurements the upper critical magnetic field Hc2 (T), the irreversibility line Hirr (T) and the crossover field HCrossOver (T) were located. These three parameters allowed us to establish a phase diagram of the studied material where limits of each vortex phase are sketched in order to optimize its applicability as a practical high temperature superconductor used for diverse purposes.

Small, modular and economically attractive fusion enabled by high temperature superconductors

2019 ◽  
Vol 377 (2141) ◽  
pp. 20180354 ◽  
Author(s):  
Dennis Whyte
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Magnetic Fields ◽  
Current Density ◽  
High Temperature Superconductors ◽  
Fusion Energy ◽  
High Magnetic Fields ◽  
Operating Temperatures ◽  
The Magnetic Field ◽  
Game Changer

The advantages of high magnetic fields in tokamaks are reviewed, and why they are important in leading to more compact tokamaks. A brief explanation is given of what limits the magnetic field in a tokamak, and why high temperature superconductors (HTSs) are a game changer, not just because of their higher magnetic fields but also for reasons of higher current density and higher operating temperatures. An accelerated pathway to fusion energy is described, defined by the SPARC and ARC tokamak designs. This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.

Specific features of penetration and trapping of a magnetic flux in film and bulk YBCO high-temperature superconductors

2018 ◽  
Vol 32 (31) ◽  
pp. 1850346
Author(s):  
Kh. R. Rostami
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Magnetic Flux ◽  
External Field ◽  
High Temperature Superconductors ◽  
Interaction Mechanism ◽  
Differential Method ◽  
Bulk Ybco ◽  
The Magnetic Field ◽  
Insight Into

An oscillatory differential method of local diagnostics of superconductors is applied to the analysis of the trapped magnetic flux and the effective demagnetization factor in YBCO samples. Regular steps over certain intervals of the external field are observed on the magnetic-field dependence of these parameters. It is demonstrated that, as the external field increases, crystallites in a sample are decomposed into sub- and nanocrystallites with a size much less than the penetration depth [Formula: see text] of the magnetic field. The first critical thermodynamic magnetic fields of sub- and nanocrystallites are determined. These results allow one to reveal the interaction mechanism between magnetic and crystalline microstructures of superconductors and provide a deeper insight into the physical processes that occur in high-temperature superconductors (HTSCs) in a magnetic field.

Sign in / Sign up

Export Citation Format

Share Document