scholarly journals Helical magnetic self-organization of plasmas in toroidal pinches with transport barriers formation

2020 ◽  
Vol 230 ◽  
pp. 00013
Author(s):  
Marco Veranda ◽  
Daniele Bonfiglio ◽  
Susanna Cappello ◽  
Luis Chacòn ◽  
Dominique Frank Escande ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Self Organization ◽  
Radial Magnetic Field ◽  
Hot Plasma ◽  
Natural Tendency ◽  
Transport Barriers ◽  
Reversed Field ◽  
Field Lines ◽  
Two Parameters ◽  
Connection Length

Nonlinear MHD modeling of toroidal pinch configurations for hot plasma magnetic confinement describes several features of the helical self-organization process, which is observed in both reversed-field pinches and tokamaks. It can also give a hint on why transport barriers are formed, by far one of the more interesting observations in experiments. The work tackles these two topics, helical self-organization and transport barriers formation - adding further information and examples to the results already presented in [Veranda, et al, Nucl.Fus. 60 016007 (2020)]. Regarding the topic of helical self-organization, a synthesis of the results obtained by a 3D nonlinear viscoresistive magnetohydrodynamics model will be presented. Modelling predicts a technique to “channel” reversed-field pinches into a chosen macroscopic helical shape and also predicts that the features of such helical self-organization, studied in the RFX-mod experiment in Padova, depend on two parameters only: plasma dissipation coefficients and edge radial magnetic field. They can be exploited to calm the natural tendency of reversed-field pinches to a “sawtoothing” dynamics, i.e. by decreasing visco-resistive dissipation and using helical edge fields not resonating with the plasma safety factor. Regarding the MHD description of the process of formation of transport barriers by magnetic chaos healing, we will describe the computation of Lagrangian structures, hidden in the weakly stochastic behaviour of magnetic field lines, acting as barriers to the transport. The radial position of such structures is observed to correspond to higher gradients of magnetic field lines connection length to the edge: this provides a further indication of their possible role in the formation of electron temperature barriers.

Theory and observations of switchbacks’ evolution in the solar wind

2021 ◽  
Author(s):  
Anna Tenerani ◽  
Marco Velli ◽  
Lorenzo Matteini
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Radial Magnetic Field ◽  
Open Questions ◽  
Coronal Activity ◽  
Turbulent Heating ◽  
Field Lines ◽  
Radial Evolution ◽  
Field Correlation

<p>Alfvénic fluctuations represent the dominant contributions to turbulent fluctuations in the solar wind, especially, but not limited to, the fastest streams with velocity of the order of 600-700 km/s. Alfvénic fluctuations can contribute to solar wind heating and acceleration via wave pressure and turbulent heating. Observations show that such fluctuations are characterized by a nearly constant magnetic field amplitude, a condition which remains largely to be understood and that may be an indication of how fluctuations evolve and relax in the expanding solar wind. Interestingly, measurements from Parker Solar Probe have shown the ubiquitous and persistent presence of the so-called switchbacks. These are magnetic field lines which are strongly perturbed to the point that they produce local inversions of the radial magnetic field. The corresponding signature of switchbacks in the velocity field is that of local enhancements in the radial speed (or jets) that display the typical velocity-magnetic field correlation that characterizes Alfvén waves propagating away from the Sun. While there is not yet a general consensus on what is the origin of switchbacks and their connection to coronal activity, a first necessary step to answer these important questions is to understand how they evolve and how long they can persist in the solar wind. Here we investigate the evolution of switchbacks. We address how their evolution is affected by parametric instabilities and the possible role of expansion, by comparing models with the observed radial evolution of the fluctuations’ amplitude. We finally discuss what are the implications of our results for models of switchback generation and related open questions.</p>

scholarly journals A rotating and magnetized three-dimensional hot plasma equilibrium in a gravitational field

2015 ◽  
Vol 81 (3) ◽  
Author(s):  
Peter J. Catto ◽  
Sergei I. Krasheninnikov
Keyword(s):  
Magnetic Field ◽  
Gravitational Field ◽  
Equatorial Plane ◽  
Three Dimensional ◽  
Rotation Frequency ◽  
High Plasma ◽  
Plasma Pressure ◽  
Hot Plasma ◽  
Field Lines ◽  
Open Magnetic Field

A rotating and magnetized three-dimensional axisymmetric equilibrium for hot plasma confined by a gravitational field is found. The plasma density and current can exhibit strong equatorial plane localization, resulting in disk equilibria with open magnetic field lines. The associated equatorial plane pinching results in magnetic field flaring, implying a strong gravitational squeezing of the plasma carrying ambient magnetic field lines toward the gravitational source. At high plasma pressure, the magnetic field becomes strongly radial outside the disk. The model predicts the rotation frequency bound, the condition for a plasma disk, and the requirement for strong magnetic field flaring.

Ganymede’s magnetic footprint mapping: Modeling and HST observations

2020 ◽  
Author(s):  
Tatphicha Promfu ◽  
Suwicha Wannawichian ◽  
Jonathan Nichols ◽  
John Clarke
Keyword(s):  
Magnetic Field ◽  
Hubble Space Telescope ◽  
Volcanic Eruptions ◽  
Plasma Pressure ◽  
Magnetic Field Mapping ◽  
Hot Plasma ◽  
Pressure Anisotropy ◽  
Magnetic Field Model ◽  
Field Lines ◽  
The Magnetic Field

<p>In this work, the locations of observed Ganymede’s magnetic footprint were compared with the locations predicted by the magnetic field model under different plasma conditions. The shifts of Ganymede's magnetic footprint locations from average footpath given by Grodent et al. (2008) were analyzed. The average path is created from about 1000 images taken by instruments onboarded Hubble Space Telescope (HST). The position shifts indicate the variation of magnetic field line mapping from Ganymede to Jupiter’s ionosphere. The two sets of data from HST were analyzed to obtain the locations of Ganymede’s magnetic footprint in 2007 and 2016. For both sets of data, at longitude ranging approximately from 170° to 180°, we found that the locations were significantly shifted in poleward direction between 0.5° to 2° from the average footpath. Different from data in May 2007, the Ganymede’s magnetic footprint locations in May 2016 at longitude about 160° could possibly locate in equatorward direction. At orbital distance of Ganymede about 15 R<sub>J</sub>, in Jupiter’s middle magnetosphere, there is strong influence of plasma, whose major source is Io’s volcanic eruptions. Thus, the variations of plasma resulting in the stretching of magnetic field lines affect the magnetic field mapping from Ganymede to ionosphere. Furthermore, based on the magnetodisc model, the hot plasma pressure anisotropy strongly influences the stretching of the field lines and the mapped locations of Ganymede’s footprint in ionosphere to be shifted in either poleward or equatorward directions. In this study, we detected both poleward and equatorward shifts in different observations, whose connection with the plasma environment in the middle magnetosphere awaits for further study.</p>

scholarly journals Island divertor configuration design for a quasi-axisymmetric stellarator CFQS

2020 ◽  
Vol 86 (4) ◽  
Author(s):  
S. Okamura ◽  
H. Liu ◽  
A. Shimizu ◽  
S. Kinoshita ◽  
M. Isobe ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Peripheral Region ◽  
Field Configuration ◽  
Magnetic Field Configuration ◽  
The Core ◽  
Confinement Region ◽  
Field Lines ◽  
Under Construction ◽  
Connection Length ◽  
The Magnetic Field

A magnetic field configuration of an island divertor for a quasi-axisymmetric stellarator (CFQS) is proposed. The configuration incorporates large islands surrounding the core confinement region. The interface between the core region and the peripheral region of the island divertor is a clear magnetic separatrix similar to a tokamak divertor. The structure of divertor magnetic field lines is very regular without stochasticity and the connection length is sufficiently long for good divertor performance. Such a divertor configuration is produced in the magnetic field configuration for the CFQS device, which is now under construction in China.

Self-organization, anomalous resistance and anomalous heating in magnetized plasmas

1998 ◽  
Vol 59 (1) ◽  
pp. 103-123 ◽  
Author(s):  
Z. YOSHIDA ◽  
N. INOUE ◽  
T. FUJITA ◽  
K. HATTORI ◽  
S. ISHIDA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
The Self ◽  
Self Organization ◽  
Plasma Current ◽  
Toroidal Plasma ◽  
Plasma Device ◽  
Field Lines ◽  
Kink Instability ◽  
Fluctuation Energy ◽  
Mhd Relaxation

The nonlinear dynamics and structure of plasmas with tightly twisted magnetic field lines have been studied using a toroidal plasma device. Stepwise magnetohydrodynamic (MHD) relaxation occurs, resulting in a discontinuous change in the pitch of magnetic field lines. This discrete nature of the pitch stems from the instability of kink (torsional) modes. The MHD relaxation stabilizes kink modes by selecting (self-organizing) appropriate pitches. The self-organized state displays the characteristic of a ‘dissipative structure’ in that it is accompanied by enhanced energy dissipation; the global resistance of the plasma current is substantially enhanced. The magnetic energy, which is generated by the internal plasma current, first changes into fluctuation energy through the kink instability, and then it goes mainly to ion thermal energy through viscous dissipation of the fluctuating flow. The viscosity dissipates the fluctuation energy with conservation of helicity. The self-organization of the stabilized magnetic field is characterized by the preferential conservation of the helicity.

Stochastic magnetic field lines diffusion in a toroidal configuration (Tokamak)

2000 ◽  
Vol 12 (2) ◽  
pp. 145-153 ◽  
Author(s):  
R. Tabet ◽  
H. Imrane ◽  
D. Saifaoui ◽  
A. Dezairi ◽  
F. Miskane
Keyword(s):  
Magnetic Field ◽  
Field Lines ◽  
Stochastic Magnetic Field

Exact nonlinear wave solutions of the incompressible magnetohydrodynamic equations in a sheared magnetic field

1990 ◽  
Vol 44 (1) ◽  
pp. 25-32 ◽  
Author(s):  
Hiromitsu Hamabata
Keyword(s):  
Magnetic Field ◽  
Incompressible Fluid ◽  
Large Amplitude ◽  
Uniform Magnetic Field ◽  
Magnetohydrodynamic Equations ◽  
Wave Solutions ◽  
Field Lines ◽  
Incompressible Magnetohydrodynamic Equations ◽  
Physical Quantities ◽  
Nonlinear Wave Solutions

Exact wave solutions of the nonlinear jnagnetohydrodynamic equations for a highly conducting incompressible fluid are obtained for the cases where the physical quantities are independent of one Cartesian co-ordina.te and for where they vary three-dimensionally but both the streamlines and magnetic field lines lie in parallel planes. It is shown that there is a class of exact wave solutions with large amplitude propagating in a straight but non-uniform magnetic field with constant or non-uniform velocity.

scholarly journals Magnetic nulls in interacting dipolar fields

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Todd Elder ◽  
Allen H. Boozer
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Magnetic Flux Tube ◽  
Electron Inertia ◽  
Characteristic Spatial Scale ◽  
Field Lines ◽  
Dipolar Fields ◽  
Time Required ◽  
Magnetic Null ◽  
The Magnetic Field

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance $\varDelta _d$ . Electron inertia ensures $\varDelta _d\gtrsim c/\omega _{pe}$ . The lines that lie within a magnetic flux tube of radius $\varDelta _d$ at the place where the field strength $B$ is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where $B=0$ vanishes, then distinguishable lines come no closer to the null than $\approx (a^2c/\omega _{pe})^{1/3}$ , where $a$ is a characteristic spatial scale of the magnetic field. The behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

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