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

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.

scholarly journals Transition to subcritical turbulence in a tokamak plasma

2016 ◽  
Vol 82 (6) ◽  
Author(s):  
F. van Wyk ◽  
E. G. Highcock ◽  
A. A. Schekochihin ◽  
C. M. Roach ◽  
A. R. Field ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Initial Perturbation ◽  
Outer Core ◽  
Transition To Turbulence ◽  
Tokamak Plasma ◽  
Ion Temperature ◽  
Flow Shear ◽  
Ion Temperature Gradient ◽  
Stability Threshold ◽  
Accretion Flows

Tokamak turbulence, driven by the ion-temperature gradient and occurring in the presence of flow shear, is investigated by means of local, ion-scale, electrostatic gyrokinetic simulations (with both kinetic ions and electrons) of the conditions in the outer core of the Mega-Ampere Spherical Tokamak (MAST). A parameter scan in the local values of the ion-temperature gradient and flow shear is performed. It is demonstrated that the experimentally observed state is near the stability threshold and that this stability threshold is nonlinear: sheared turbulence is subcritical, i.e. the system is formally stable to small perturbations, but, given a large enough initial perturbation, it transitions to a turbulent state. A scenario for such a transition is proposed and supported by numerical results: close to threshold, the nonlinear saturated state and the associated anomalous heat transport are dominated by long-lived coherent structures, which drift across the domain, have finite amplitudes, but are not volume filling; as the system is taken away from the threshold into the more unstable regime, the number of these structures increases until they overlap and a more conventional chaotic state emerges. Whereas this appears to represent a new scenario for transition to turbulence in tokamak plasmas, it is reminiscent of the behaviour of other subcritically turbulent systems, e.g. pipe flows and Keplerian magnetorotational accretion flows.

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.

Neoclassical diffusion of a finite-β, tokamak plasma

1972 ◽  
Vol 7 (3) ◽  
pp. 427-434 ◽  
Author(s):  
Aldo Nocentini
Keyword(s):  
Electromagnetic Field ◽  
Aspect Ratio ◽  
Cross Section ◽  
Circular Cross Section ◽  
External Electromagnetic Field ◽  
Tokamak Plasma ◽  
Temperature Profiles ◽  
Small Aspect Ratio ◽  
Magnetic Surfaces ◽  
Ratio Limit

The neoclassical diffusion in a tokamak is calculated for a finite-β plasma. The flux of the particles is shown to be substantially unchanged, with respect to the low-β case. The ‘equilibrium’ equation is derived. From it the magnetic surfaces can be obtained, once the external electromagnetic field and the density and temperature profiles are given. The case of magnetic surfaces with circular cross-section, in the small aspect ratio limit, is considered in detail.

Magnetohydrodynamic equilibrium interpretation of low-aspect-ratio tokamak plasma

2016 ◽  
Vol 171 (7-8) ◽  
pp. 644-650 ◽  
Author(s):  
Sung-Gil Ri ◽  
Hak-Son Jin ◽  
Chol-Jun Hwang
Keyword(s):  
Aspect Ratio ◽  
Tokamak Plasma ◽  
Low Aspect Ratio

Anomalous parallel momentum transport due to E×B flow shear in a tokamak plasma

2009 ◽  
Vol 16 (9) ◽  
pp. 092303 ◽  
Author(s):  
F. J. Casson ◽  
A. G. Peeters ◽  
Y. Camenen ◽  
W. A. Hornsby ◽  
A. P. Snodin ◽  
...  
Keyword(s):  
Momentum Transport ◽  
Tokamak Plasma ◽  
Flow Shear ◽  
Parallel Momentum

Modification of MnS inclusion by tellurium in 38MnVS6 micro-alloyed steel

2020 ◽  
Vol 117 (6) ◽  
pp. 615
Author(s):  
Ping Shen ◽  
Lei Zhou ◽  
Qiankun Yang ◽  
Zhiqi Zeng ◽  
Kenan Ai ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Aspect Ratio ◽  
Strong Influence ◽  
Experimental Results ◽  
Alloyed Steel ◽  
Equivalent Diameter ◽  
Small Aspect Ratio ◽  
Steel Quality ◽  
Eds Analysis ◽  
Micro Alloyed Steel

In 38MnVS6 steel, the morphology of sulfide inclusion has a strong influence on the fatigue life and machinability of the steel. In most cases, the MnS inclusions show strip morphology after rolling, which significantly affects the steel quality. Usually, the MnS inclusion with a spherical morphology is the best morphology for the steel quality. In the present work, tellurium was applied to 38MnVS6 micro-alloyed steel to control the MnS inclusion. Trace tellurium was added into 38MnVS6 steel and the effect of Te on the morphology, composition, size and distribution of MnS inclusions were investigated. Experimental results show that with the increase of Te content, the equivalent diameter and the aspect ratio of inclusion decrease strikingly, and the number of inclusions with small aspect ratio increases. The inclusions are dissociated and spherized. The SEM-EDS analysis indicates that the trace Te mainly dissolves in MnS inclusion. Once the MnS is saturated with Te, MnTe starts to generate and wraps MnS. The critical Te/S value for the formation of MnTe in the 38MnV6 steel is determined to be approximately 0.075. With the increase of Te/S ratio, the aspect ratio of MnS inclusion decreases and gradually reaches a constant level. The Te/S value in the 38MnVS6 steel corresponding to the change of aspect ratio from decreasing to constant ranges from 0.096 to 0.255. This is most likely to be caused by the saturation of Te in the MnS inclusion. After adding Te in the steel, rod-like MnS inclusion is modified to small inclusion and the smaller the MnS inclusion, the lower the aspect ratio.

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