Enhancement of neoclassical transport coefficients by a poloidal electric field in tokamaks

1983 ◽  
Vol 26 (8) ◽  
pp. 2140 ◽  
Author(s):  
C. S. Chang
Keyword(s):  
Electric Field ◽  
Transport Coefficients ◽  
Neoclassical Transport

Monte Carlo Simulation of Neoclassical Transport in Axisymmetric and Ripple Tokamaks

1982 ◽  
Vol 37 (8) ◽  
pp. 899-905 ◽  
Author(s):  
W. Lötz ◽  
J. Nührenberg
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Electric Field ◽  
Pitch Angle ◽  
Particle Distribution ◽  
Transport Coefficients ◽  
Angle Scattering ◽  
Wide Range ◽  
Neoclassical Transport

Simple axisymmetric and ripple tokamak model fields are used to compute neoclassical trans-port coefficients by Monte Carlo simulation over a wide range of mean free paths in the approximation of small gyroradius. Further assumptions are a monoenergetic particle distribution which is only subject to pitch angle scattering and a vanishing electric field. Pfirsch-Schlüter, plateau, banana and ripple transport coefficients are obtained. In the ripple regime the description is unified by introducing the concept of an effective ripple. Cases in which ripple transport is diminished due to collisionless detrapping are observed

Global δf particle simulation of neoclassical transport and ambipolar electric field in general geometry

2004 ◽  
Vol 164 (1-3) ◽  
pp. 178-182 ◽  
Author(s):  
W.X. Wang ◽  
W.M. Tang ◽  
F.L. Hinton ◽  
L.E. Zakharov ◽  
R.B. White ◽  
...  
Keyword(s):  
Electric Field ◽  
Particle Simulation ◽  
Neoclassical Transport ◽  
General Geometry

scholarly journals Theoretical Answers to Some Experimental Questions about Gaseous Ion Transport

1997 ◽  
Vol 50 (3) ◽  
pp. 671 ◽  
Author(s):  
Larry A. Viehland
Keyword(s):  
Electric Field ◽  
Ion Transport ◽  
Cross Sections ◽  
Diffusion Coefficients ◽  
Transport Coefficients ◽  
Resonant Scattering ◽  
Molecular Ions ◽  
Zero Field ◽  
Gas Temperature ◽  
Perpendicular Diffusion

It is shown that the diffusion coefficients parallel to the electric field in an ion swarm experiment are greater than the perpendicular diffusion coefficients at low values of E/N, the ratio of the electric field strength to the gas number density, but that at high E/N the two are approximately equal or the inequality is reversed. For electron swarms the inequalities are the reverse of those for ion swarms, unless there is a significant Ramsauer minimum in the momentum-transfer cross section. A second point is that for many ion–atom systems the zero-field mobility is not close to its polarisation limit even when the gas temperature is 4.35 K. It is also shown that the unusual mobilities observed for Ar+ ions in He gas at 4.35 K are not due to quantum-mechanical (resonant scattering) effects as postulated by the experimenters. Finally, it is shown that it is possible to compute gaseous ion transport coefficients for molecular ions from a knowledge of the fundamental interaction potentials rather than from assumed models for the cross sections.

scholarly journals Use of Transport Coefficients to Calculate Properties of Electrode Sheaths of Electric Arcs

1997 ◽  
Vol 50 (3) ◽  
pp. 539 ◽  
Author(s):  
J. J. Lowke ◽  
J. C. Quartel
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Cathode Surface ◽  
Transport Coefficients ◽  
Electric Arcs ◽  
Charge Effects ◽  
Positive Ions ◽  
Thermionic Cathodes ◽  
Principal Source ◽  
Electrode Sheath

Particle conservation equations for electrons and positive ions, together with Poisson"s equation to account for space-charge effects on the electric field, have been solved for the electrode sheath regions of electric arcs. For thermionic cathodes and the anode, we find that the ambipolar diffusion approximation is generally valid. At the surface of the anode we find that there is generally a small retarding electric field. For non-thermionic cathodes and no ionisation due to the electric field in the sheath, we calculate unrealistically high sheath voltages and even then, find that the electric fields at the cathode surface are insufficient for field emission. It is suggested that photoionisation in the region close to the cathode may be a principal source of electrons for non-thermionic cathodes.

scholarly journals Collisional transport of impurities with flux-surface varying density in stellarators

2018 ◽  
Vol 84 (4) ◽  
Author(s):  
S. Buller ◽  
H. M. Smith ◽  
P. Helander ◽  
A. Mollén ◽  
S. L. Newton ◽  
...  
Keyword(s):  
Electric Field ◽  
Radial Electric Field ◽  
Magnetic Confinement ◽  
Vacuum Field ◽  
Flux Surface ◽  
Impurity Density ◽  
Impurity Transport ◽  
Neoclassical Transport ◽  
Potential Perturbation ◽  
Analytic Models

High-$Z$impurities in magnetic-confinement devices are prone to develop density variations on the flux surface, which can significantly affect their transport. In this paper, we generalize earlier analytic stellarator calculations of the neoclassical radial impurity flux in the mixed-collisionality regime (collisional impurities and low-collisionality bulk ions) to include the effect of such flux-surface variations. We find that only in the homogeneous density case is the transport of highly collisional impurities (in the Pfirsch–Schlüter regime) independent of the radial electric field. We study these effects for a Wendelstein 7-X (W7-X) vacuum field, with simple analytic models for the potential perturbation, under the assumption that the impurity density is given by a Boltzmann response to a perturbed potential. In the W7-X case studied, we find that larger amplitude potential perturbations cause the radial electric field to dominate the transport of the impurities. In addition, we find that classical impurity transport can be larger than the neoclassical transport in W7-X.

Neoclassical transport coefficients for finite-aspect-ratio and bean-shaped tokamak plasmas

1987 ◽  
Vol 30 (4) ◽  
pp. 1152 ◽  
Author(s):  
E. C. Crume ◽  
C. O. Beasley ◽  
S. P. Hirshman ◽  
W. I. van Rij
Keyword(s):  
Aspect Ratio ◽  
Transport Coefficients ◽  
Tokamak Plasmas ◽  
Neoclassical Transport
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