Poloidal rotation, density asymmetries, and momentum confinement in tokamak experiments

Abstract

Poloidal rotation speeds and density asymmetries are calculated for the deuterium and dominant carbon (oxygen) impurity ions in discharges in the Axially Symmetric Divertor Experiment (ASDEX) [Proceedings of the 13th Conference on Plasma Physics and Controlled Fusion Research, (International Atomic Energy Agency, Vienna, 1991), p. 325], Doublet III (DIII) [Nucl. Fusion 26, 543 (1986)], Impurity Studies Experiment (ISX-B) [Nucl. Fusion 23, 1017 (1983)], Joint European Torus (JET) [Nucl. Fusion 31, 31 (1991)] and Tokamak Fusion Test Reactor (TFTR) (National Technical Information Document No. PB92177187) for which vφ∼vth for the ions. These poloidal rotation speeds and density asymmetries are used to evaluate the neoclassical gyroviscous model for the momentum confinement time. The rather good agreement with experimental momentum confinement times obtained over this wide range of plasma parameters provides a measure of confidence in the calculated density asymmetries and poloidal rotation, as well as demonstrating that neoclassical calculations can predict momentum confinement in tokamaks.

Extension of neoclassical rotation theory for tokamaks to realistically account for the geometry of magnetic flux surfaces

“…More details on the S-S poloidal rotation model can be found in [18,42]. Earlier studies with the S-S model [12,[30][31][32][33] have developed a neoclassical plasma rotation theory based on the circular flux surface geometry, and these previous calculations were compared to actual velocity measurements [30]. Although the calculated toroidal velocities were off by about a factor of two, these studies proved the possibility of using simple analytic flux surface geometry models in this type of neoclassical rotation and the related momentum transport calculations but concluded that higher accuracy could be achieved with a more accurate flux surface geometry since poloidal asymmetries are closely related to the geometric expansion, compression, and elongation of flux surfaces [30].…”

“…Unlike those of the circular model used in earlier studies [12,[30][31][32][33], FSAs in the Miller model do not reduce to simple analytic forms, thus must be numerically computed separately and imported into the final computation code. Note here that the circular model is simply a special case of the Miller model with elongation κ = 1, triangularity δ = 0 and no Shafranov shift.…”

Neoclassical theory for rotation and impurity transport in tokamaks with neutral beam injection

“…For example, in enhanced reverse shear plasmas in the Tokamak Fusion Test Reactor 1,2 ͑TFTR͒ and negative central shear plasmas in DIII-D 3 turbulence is suppressed and the standard neoclassical expressions predict the measured ion thermal conductivity rather well. Calculations of momentum confinement time based on neoclassical gyroviscous theory have agreed, 4 rather well with measurements in several tokamaks. In H-mode ͑high confinement mode͒ plasmas in the Joint European Torus ͑JET͒, the measured value of radial impurity flow has been shown 5 to be in agreement with neoclassical theory, and neoclassical temperature gradient screening may explain the expulsion of carbon from the core in JET hot ion mode discharges.…”

The role of neoclassical convection in the confinement improvement of plasmas with impurity injection in DIII-D

“…8. Encouraged by the success of gyroviscous momentum transport rates in predicting measured momentum confinement times in the shots which we wish to analyze in this paper, 7 as well as in several other experiments, 9 we use a gyroviscous 10 expression for the viscous energy loss rate This neoclassical particle flux calculation model is summarized in Ref.…”