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.

Sheared slab ηi instability in tokamak plasma with negative magnetic shear

1998 ◽  
Vol 5 (4) ◽  
pp. 959-965 ◽  
Author(s):  
Jiquan Li ◽  
Lin Huang ◽  
Wenxiao Qu
Keyword(s):  
Tokamak Plasma ◽  
Magnetic Shear

Stability of a tokamak plasma with diffuse toroidal rotation

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
O. E. López ◽  
L. Guazzotto
Keyword(s):  
Shooting Method ◽  
Tokamak Plasma ◽  
Solution Technique ◽  
Large Aspect Ratio ◽  
Internal Resonances ◽  
Flow Shear ◽  
Magnetic Shear ◽  
The Stability ◽  
External Kink ◽  
Selection Of

The present work considers the stability of a high- $\beta$ , large aspect ratio, circular plasma with diffuse profiles for the safety factor and the angular toroidal frequency (López & Guazzotto, Phys. Plasmas, vol. 24, 032501). An application of the Frieman–Rotenberg formalism results in a system of scalar eigenmode equations whose coupling is retained at the plasma–vacuum transition but is disregarded across the plasma column, which is a standard practice. The solution technique consists of a multidimensional shooting method for the poloidal harmonics; robust initial guesses are constructed by solving the dispersion relation in the static scenario with vanishing magnetic shear. Flow shear appears as a high- $\beta$ toroidal contribution, and we illustrate its destabilizing influence on $n=1$ external kink modes in the presence of ideal and resistive walls. Internal resonances are avoided by means of the selection of appropriate equilibrium parameters. The stabilizing influence of a finite positive average magnetic shear is also exemplified.

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

Axisymmetrization and vorticity-gradient intensification of an isolated two-dimensional vortex through filamentation

1987 ◽  
Vol 178 ◽  
pp. 137-159 ◽  
Author(s):  
M. V. Melander ◽  
J. C. Mcwilliams ◽  
N. J. Zabusky
Keyword(s):  
Aspect Ratio ◽  
Second Order ◽  
Rate Of Change ◽  
Two Dimensional ◽  
Final State ◽  
Diagnostic Algorithms ◽  
Dissipative Fluid ◽  
New Formula ◽  
Corotating Frame

We consider the evolution of an isolated elliptical vortex in a weakly dissipative fluid. It is shown computationally that a spatially smooth vortex relaxes inviscidly towards axisymmetry on a circulation timescale as the result of filament generation. Heuristically, we derive a simple geometrical formula relating the rate of change of the aspect ratio of a particular vorticity contour to its orientation relative to the streamlines (where the orientation is defined through second-order moments). Computational evidence obtained with diagnostic algorithms validates the formula. By considering streamlines in a corotating frame and applying the new formula, we obtain a detailed kinematic understanding of the vortex's decay to its final state through a primary and a secondary breaking. The circulation transported into the filaments although a small fraction of the total, breaks the symmetry and is the chief cause of axisymmetrization.

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 Electrostatic potential variations on stellarator magnetic surfaces in low collisionality regimes

2018 ◽  
Vol 84 (4) ◽  
Author(s):  
Iván Calvo ◽  
José Luis Velasco ◽  
Félix I. Parra ◽  
J. Arturo Alonso ◽  
José Manuel García-Regaña
Keyword(s):  
Aspect Ratio ◽  
Electrostatic Potential ◽  
Magnetic Surface ◽  
Radial Transport ◽  
Analytical Results ◽  
Magnetic Surfaces ◽  
Neoclassical Transport ◽  
Numerical Tools ◽  
Transport Problems ◽  
Computational Resources

The component of the neoclassical electrostatic potential that is non-constant on the magnetic surface, that we denote by$\tilde{\unicode[STIX]{x1D711}}$, can affect radial transport of highly charged impurities, and this has motivated its inclusion in some modern neoclassical codes. The number of neoclassical simulations in which$\tilde{\unicode[STIX]{x1D711}}$is calculated is still scarce, partly because they are usually demanding in terms of computational resources, especially at low collisionality. In this paper the size, the scaling with collisionality and with aspect ratio and the structure of$\tilde{\unicode[STIX]{x1D711}}$on the magnetic surface are analytically derived in the$1/\unicode[STIX]{x1D708}$,$\sqrt{\unicode[STIX]{x1D708}}$and superbanana-plateau regimes of stellarators close to omnigeneity; i.e. stellarators that have been optimized for neoclassical transport. It is found that the largest$\tilde{\unicode[STIX]{x1D711}}$that the neoclassical equations admit scales linearly with the inverse aspect ratio and with the size of the deviation from omnigeneity. Using a model for a perturbed omnigenous configuration, the analytical results are verified and illustrated with calculations by the codeKNOSOS. The techniques, results and numerical tools employed in this paper can be applied to neoclassical transport problems in tokamaks with broken axisymmetry.

Second-order self-energy for the Anderson model analytical results

1979 ◽  
Vol 91 (1) ◽  
pp. 355-360 ◽  
Author(s):  
J. Zieliński ◽  
B. Kozarzewski
Keyword(s):  
Anderson Model ◽  
Second Order ◽  
Self Energy ◽  
Analytical Results

scholarly journals Flow shear induced fluctuation suppression in finite aspect ratio shaped tokamak plasma

1995 ◽  
Vol 2 (5) ◽  
pp. 1648-1651 ◽  
Author(s):  
T. S. Hahm ◽  
K. H. Burrell
Keyword(s):  
Aspect Ratio ◽  
Tokamak Plasma ◽  
Flow 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 Linear Hydrodynamic Stability of Fluid Flow in Curved Rectangular Ducts: Semi-Analytical Study

2019 ◽  
Vol 35 (5) ◽  
pp. 747-765 ◽  
Author(s):  
H. Nowruzi ◽  
H. Ghassemi ◽  
S. S. Nourazar
Keyword(s):  
Fluid Flow ◽  
Aspect Ratio ◽  
Eigenvalue Problem ◽  
Flow Instability ◽  
Wave Number ◽  
Dean Number ◽  
Analytical Technique ◽  
Dean Flow ◽  
Aspect Ratios ◽  
Analytical Results

ABSTRACTIn the current study, for the first time, a semi-analytical technique is used for solving eigenvalue problem arising from linear hydrodynamics stability of fluid flow through the curved rectangular ducts at different curvature ratios and aspect ratios. To this accomplishment, symmetric disturbances are assumed and the Homotopy perturbation method (HPM) is applied to solve our eigenvalue problem for curvature ratios ranging from 0.01 to 0.8 and aspect ratios ranging from 0.05 to 20. Our semi-analytical results are validated through the existing numerical and experimental data, showing good agreement. The semi-analytical results indicate that, as the curvature ratio increases the critical Dean number (Dnc) is increased and the flow becomes more stable, especially for aspect ratios lower than 1.Moreover, for all intended curvature ratios, irregular behavior in variation of Dnc is detected by an increase in the aspect ratio. So that, the Dnc is decreased when the aspect ratio increases from 0.05 up to 1 and the fluid flow becomes unstable. When the aspect ratio is increased from 1 to 5, it causes to increase the Dnc and fluid flow becomes stable. Furthermore, when the aspect ratio increases from 5 to 20, the Dnc is decreased again. In addition, Dnc and eigenvalues of critical complex wave number corresponding to Dnc for the onset of Dean flow instability is reported under different curvature ratios and aspect ratios.

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