Formation of an internal transport barrier and magnetohydrodynamic activity in experiments with the controlled density o
- PDF / 363,443 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 55 Downloads / 172 Views
KS
Formation of an Internal Transport Barrier and Magnetohydrodynamic Activity in Experiments with the Controlled Density of Rational Magnetic Surfaces in the T10 Tokamak K. A. Razumova, V. F. Andreev, I. S. Bel’bas, A. V. Gorshkov, A. Yu. Dnestrovskij, K. S. Dyabilin, A. Ya. Kislov, S. E. Lysenko, G. E. Notkin, N. N. Timchenko, A. N. Chudnovskiy, and D. A. Shelukhin National Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia email: [email protected] Received January 14, 2013; in final form, March 21, 2013
Abstract—Results are presented from experiments on the formation of an internal electron transport barrier near the q = 1.5 rational surface in the T10 tokamak. The experiments were carried out in the regime with offaxis electron cyclotron resonance (ECR) heating followed by a fast plasma current rampup. After sup pressing sawtooth oscillations by offaxis ECR heating, an internal transport barrier began to form near the q = 1.5 rational surface. In the phase of the current rampup, the quality of the transport barrier improved; as a result, the plasma energy confinement time increased 2–2.5 times. The intentionally produced flattening of the profile of the safety factor q(r) insignificantly affected magnetohydrodynamic activity in the plasma column in spite of the theoretical possibility of formation of substantial m/n = 3/2 and 2/1 magnetic islands. Conditions are discussed under which the flattening of the profile of the safety factor q near loworder ratio nal surfaces leads to the formation of either an internal transport barrier or the development of an island mag netic structure induced by tearing modes. DOI: 10.1134/S1063780X13090079
1. INTRODUCTION The most important phenomena that need to be understood in the physics of plasma confinement are the selfconsistent profile of the plasma pressure and the external and internal transport barriers (ETBs and ITBs, respectively). Analysis of experiments on the formation of a controlled profile of the safety factor shows that electron ITBs form in regions with a low density of rational magnetic surfaces [1–3], in the vicinities of loworder rational surfaces. Theoretical analysis [4–7] shows that, when the numbers of mag netohydrodynamic (MHD) modes are limited from above (m < M and n = q/M < N), zones in which the decrease in the transport rate is caused by a decrease in the density of rational magnetic surfaces can form in the vicinities of loworder rational magnetic surfaces. This leads to spatial discontinuities of the regions where the modes overlap. At the same time, the quality of the transport barrier (the ratio between the gradients of the pressure or electron temperature inside and out side the barrier) improves with decreasing dq/dr. However, the maximum mode numbers cannot be estimated analytically. Nevertheless, results of previ ous T10 experiments give the M value in the range of 20–40 [8].
Here, we present results of experiments on the transport barrier formation by controlling the q(r) pro fil
Data Loading...
