Impact of punctual flat magnetic shear on the field line transport

2015 ◽  
Vol 22 (6) ◽  
pp. 062510
Author(s):  
C. V. Abud ◽  
I. L. Caldas
Keyword(s):  
Field Line ◽  
Magnetic Shear

DIFFUSIVE TRANSPORT THROUGH A NONTWIST BARRIER IN TOKAMAKS

2007 ◽  
Vol 17 (05) ◽  
pp. 1589-1598 ◽  
Author(s):  
J. S. E. PORTELA ◽  
I. L. CALDAS ◽  
R. L. VIANA ◽  
P. J. MORRISON
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Present Model ◽  
Radial Diffusion ◽  
Diffusive Transport ◽  
Magnetic Shear ◽  
Transport Barrier ◽  
Line Structure ◽  
The Magnetic Field

The magnetic field line structure of tokamaks with reversed magnetic shear is analyzed by means of a nontwist map model that takes into account non-integrable perturbations that describe ergodic magnetic limiters. The map studied possess behavior expected of the standard nontwist map, a well-studied map, despite the different symmetries and the existence of coupled perturbations. A distinguising feature of nontwist maps is the presence of good surfaces in the reveresed shear region, and consequently the appearance of a transport barrier inside the plasma. Such barriers are observed in the present model and are seen to be very robust. Very strong perturbations are required to destroy them, and even after breaking, the transport turns out to be diffusive. Poloidal diffusion is found to be two orders of magnitude higher than radial diffusion.

scholarly journals Field Line Pitch and Local Magnetic Shear in Tokamaks

1996 ◽  
Vol 49 (6) ◽  
pp. 1121
Author(s):  
JLV Lewandowski ◽  
M Persson
Keyword(s):  
Aspect Ratio ◽  
Field Line ◽  
Second Order ◽  
Tokamak Plasma ◽  
Magnetic Shear ◽  
Analytical Results

The field line pitch and its relation to the integrated magnetic shear is discussed for a low-β tokamak plasma. Analytical results using a second order inverse aspect ratio expansion are presented and specifically discussed in the limits of peaked and fiat current profiles. The results are compared and contrasted with an earlier calculation of the local magnetic shear.

scholarly journals Non-twist field line mappings for tokamaks with reversed magnetic shear

2004 ◽  
Vol 34 (4b) ◽  
pp. 1759-1765 ◽  
Author(s):  
M. Roberto ◽  
E. C. da Silva ◽  
I. L. Caldas ◽  
R. L. Viana
Keyword(s):  
Field Line ◽  
Magnetic Shear

scholarly journals Hybrid model for drift waves in fully three-dimensional plasmas: Theory and applications.

2000 ◽  
Vol 53 (2) ◽  
pp. 259
Author(s):  
J. L. V. Lewandowski
Keyword(s):  
Field Line ◽  
Hybrid Model ◽  
Three Dimensional ◽  
Time Dependent ◽  
Drift Waves ◽  
Magnetic Shear ◽  
Electron Population ◽  
Magnetic Surfaces ◽  
Geometrical Effects ◽  
Model Equations

A novel fluid/gyro-kinetic hybrid model to study drift waves in low-pressure stellarator plasmas is presented. The ion population is modeled with the collisionless gyro-kinetic equation and the electron population is described using fluid equations. The model equations are written in straight-field-line coordinates and are valid for any magnetic configuration with closed, nested magnetic surfaces. The geometrical effects which enter the final eigenmode equations are derived and discussed in some detail. The numerical method used to solve the coupled, time-dependent, along-the-field-line equations is described. The geometrical effects are discussed in some detail. Numerical calculations are carried out for a three-field period toroidal heliac with small global magnetic shear.

Effect of magnetic shear on edge turbulence in SOL-like open field line configuration in QUEST

2018 ◽  
Vol 60 (8) ◽  
pp. 085014
Author(s):  
Santanu Banerjee ◽  
H Zushi ◽  
N Nishino ◽  
K Hanada ◽  
H Idei ◽  
...  
Keyword(s):  
Field Line ◽  
Open Field ◽  
Magnetic Shear ◽  
Line Configuration ◽  
Open Field Line

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

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