Confinement and transport studies of conventional scenarios in ASDEX Upgrade

Confinement studies of conventional scenarios, i.e. L and H modes, in ASDEX Upgrade indicate that the ion and electron temperature profiles are generally limited by a critical value of ?T/T. When this is the case the profiles are stiff: core temperatures are proportional to pedestal temperatures. Transport simulations based on turbulence driven by an ion temperature gradient show good agreement with the ion experimental data for H?modes. Studies specifically dedicated to electron transport using electron cyclotron heating with steady state and modulated powers indicate that the electron temperature profiles are also stiff. Candidates for turbulence having a threshold in ?Te/Te may be trapped electron modes and electron temperature gradient driven instabilities. The critical threshold (?Te/Te)c and the increase of the stiffness factor with temperature are found experimentally. In contrast, the density profiles are not stiff, but the variation in shape remains moderate in these conventional scenarios. As a consequence of this profile behaviour, the plasma energy is proportional to the pedestal pressure. The global confinement time increases with triangularity and can be good at densities close to the Greenwald limit at high triangularity. In this operational corner and at q95 around 4, the replacement of large type?I ELMs by small ELMs of type?II provides good confinement with very reduced peak power load on the divertor plates. This regime is believed to be adequate for a fusion reactor.

[1]  N. L. Cardozo,et al.  Perturbative transport studies in fusion plasmas , 1995 .

[2]  J. Stober,et al.  Experimental evidence for gradient length-driven electron transport in tokamaks. , 2001, Physical review letters.

[3]  W. Treutterer,et al.  Effects of triangularity on confinement, density limit and profile stiffness on H-modes on ASDEX upgrade , 2000 .

[4]  F. Sardei,et al.  Physics studies in W7-AS , 1994 .

[5]  Charlson C. Kim,et al.  Comparisons and physics basis of tokamak transport models and turbulence simulations , 2000 .

[6]  A. Hubbard,et al.  Studies of EDA H-Mode in Alcator C-Mod , 2000 .

[7]  W. Treutterer,et al.  Type II ELMy H modes on ASDEX Upgrade with good confinement at high density , 2001 .

[8]  H. Zohm,et al.  Identification of plasma-edge-related operational regime boundaries and the effect of edge instability on confinement in ASDEX Upgrade , 1997 .

[9]  M. R. Wade,et al.  Dependence of Heat and Particle Transport on the Ratio of the Ion and Electron Temperatures , 1999 .

[10]  P. Mantica,et al.  Determination of diffusive and nondiffusive transport in modulation experiments in plasmas , 1991 .

[11]  J. Stober,et al.  Closed divertor operation in ASDEX Upgrade and JET , 1999 .

[12]  R. Waltz,et al.  A gyro-Landau-fluid transport model , 1997 .

[13]  J. Manickam,et al.  Disappearance of giant ELMs and appearance of minute grassy ELMs in JT-60U high-triangularity discharges , 2000 .

[14]  Frank Jenko,et al.  Electron temperature gradient driven turbulence , 1999 .

[15]  William Dorland,et al.  Quantitative predictions of tokamak energy confinement from first‐principles simulations with kinetic effects , 1995 .

[16]  J. Weiland,et al.  Simulation of toroidal drift mode turbulence driven by temperature gradients and electron trapping , 1990 .

[17]  L. Lao,et al.  Plasma shaping, edge ballooning stability and ELM behaviour in DIII-D , 1990 .