Long-pulse improved central electron confinement in the TCV tokamak with electron cyclotron heating and current drive

Current profile tailoring by electron cyclotron heating (ECH) and current drive (ECCD) is used to improve central electron energy confinement in the TCV tokamak. Counter-ECCD on axis alone achieves this goal in a transient manner only. A stable scenario is obtained by a two-step sequence of off-axis ECH, which stabilizes magnetohydrodynamics modes, and on-axis counter-ECCD, which generates a flat or inverted current profile. This high-confinement regime, with central temperatures up to 9 keV (at a normalized beta(N) approximately 0.6), has been sustained for the entire duration of the heating pulse, or over 200 electron energy confinement times and 5 current redistribution times.     

Enhanced energy confinement and performance in a low-recycling tokamak

Extensive lithium wall coatings and liquid lithium plasma-limiting surfaces reduce recycling, with dramatic improvements in Ohmic plasma discharges in the Current Drive Experiment-Upgrade. Global energy confinement times increase by up to 6 times. These results exceed confinement scalings such as ITER98P(y,1) by 2-3 times, and represent the largest increase in energy confinement ever observed for an Ohmic tokamak plasma. Measurements of Dalpha emission indicate that global recycling coefficients decrease to approximately 0.3, the lowest documented for a magnetically confined hydrogen plasma.     

On nonquasineutrality and turbulent heat transfer in a tokamak

A new approach is proposed for describing a steady turbulent state formed far from thermodynamic equilibrium in the plasma column of a tokamak as a result of the development of microinstabilities. A fundamental feature of such a highly nonequilibrium plasma is its nonquasineutrality, i.e., the plasma properties are largely determined by electric fields localized on a scale of the order of the Debye radius. It is established that the transverse thermal diffusivity is determined by the expression

Plasma kinetic control in a tokamak

Plasma kinetic (temperature and density) control is developed in terms of optimal control theory. This involved solving a distributed parameter control problem for which no previous general theory or techniques could be practically implemented. The methodology used involves reducing the one-dimensional particle and energy transport partial differential equations into a system of ordinary differential equations. The latter are linearized and put into standard control theory format. This technique can be generalized to any distributed parameter system whose variables can be modeled as simple analytic functions of the spatial coordinates. This distributed parameter control technique shows excellent control characteristics when applied to realistic plasma temperature and density profiles. Tests were made on temperatures and densities which had been perturbed about 10% below their desired value and profiles that were significantly more peaked than the required shape. Results were obtained for a simplified model problem with specific empirical transport coefficients and a one species plasma     

Plasma confinement by a picket-fence

A current produced line cusp field is shown to confine both plasma and primary ionizing electrons.     

Plasma confinement in tokamaks with robust torus

We present a non-linear symplectic map that describes the alterations of the magnetic field lines inside the tokamak plasma due to the presence of a robust torus (RT) at the plasma edge. This RT prevents the magnetic field lines from reaching the tokamak wall and reduces, in its vicinity, the islands and invariant curve destruction due to resonant perturbations. The map describes the equilibrium magnetic field lines perturbed by resonances created by ergodic magnetic limiters (EMLs). We present the results obtained for twist and non-twist mappings derived for monotonic and non-monotonic plasma current density radial profiles, respectively. Our results indicate that the RT implementation would decrease the field line transport at the tokamak plasma edge.     

Measurement of pressure-gradient-driven currents in tokamak edge plasmas

Localized currents driven by pressure gradients play a pivotal role in the magnetohydrodynamic stability of toroidal plasma confinement devices. We have measured the currents generated in the edge of L- (low) and H- (high confinement) mode discharges on the DIII-D tokamak, utilizing the Zeeman effect in an injected lithium beam to obtain high resolution profiles of the poloidal magnetic field. We find current densities in excess of 1 MA/m2 in a 1 to 2 cm region near the peak of the edge pressure gradient. These values are sufficient to challenge edge stability theories based on specific current formation models.     

HL-lM装置杂质粒子输运与约束特性

在HL-lM装置上利用激光吹气技术,在等离子体边缘瞬态注入少量Al杂质粒子,通过对真空紫外光谱和软X射线区的杂质辐射测量,分别研究了欧姆等离子体和低杂波电流驱动等离子体两种情况下,Al杂质粒子输运与约束特性。结果表明：在欧姆等离子体和低杂波电流驱动等离子体两种情况下,等离子体中心区,在没有MHD锯齿震荡和有MHD锯齿震荡非锯齿破裂期间,杂质粒子输运基本上受新经典规律支配;在有MHD锯齿震荡锯齿破裂期间,杂质粒子输运受MHD不稳定性支配,但其时间很短(通常小于300μs),所以在这种情况下,杂质粒子输运的平均效应比新经典值稍大。而约束区杂质粒子输运则比新经典的值大很多,是反常的。在一定条件下低混杂波电流驱动可以改善等离子体粒子约束。     

Plasma confinement by a magnetic shell configuration

The confinement properties of a new magnetic shell configuration have been investigated experimentally. The diffusion coefficient D has been determined.     

Negative edge plasma currents in the SINP tokamak

A tokamak plasma discharge having an increase in duration accompanied with enhanced runaway electron flux has been experimentally studied in this paper. The discharges have been obtained by controlling the applied vertical magnetic field (B_v^applB_{\rm{v}}^{\rm{appl}}) to below a critical value. Such discharges have been observed to have ‘negative edge plasma currents’, detected using an internal Rogowskii coil (IRC). We have tried to correlate the runaway behaviour with the negative edge plasma currents and have explained that these observations are a result of beam plasma instabilities.