Transport in high normalized beta discharges on ASDEX Upgrade

An advanced high confinement mode scenario with normalized beta (βN) up to 3.5 in stationary conditions (up to 20 energy confinement times) and βN = 3.8 transiently, has been obtained in ASDEX Upgrade. For transport analysis of high βN discharges, two types of simulations have been performed with the automated system for transport analysis code. One is the simulation of the current density profile with experimental data assuming neoclassical electrical conductivity. The other is the simulation of the energy transport and the current density profile using the Weiland transport model (ion temperature gradient and trapped electron mode limit the temperature gradient length). The comparison of the simulations of the q-profiles and temperature profiles with the experimental profiles shows good agreement and demonstrates that for this plasmas regime the temperature profiles are stiff (no internal transport barrier) as in conventional H-mode discharges. The contribution of the Ohmic, bootstrap and neutral beam driven current to the total current density profiles is calculated. The sum of the non-inductively driven plasma current is in the range 50–57% of the total plasma current. Simulations with the Weiland model are performed to investigate the influence of neoclassical tearing modes, which limit confinement and achievable βN in this scenario, by comparing with the measured kinetic data. In addition, the high βN discharges are compared to the improved H-mode discharges in ASDEX Upgrade with respect to the profile stiffness, MHD activity and experimental conditions.

[1]  P J McCarthy,et al.  Reaching high poloidal beta at Greenwald density with internal transport barrier close to full noninductive current drive. , 2001, Physical review letters.

[2]  H. Zohm,et al.  High-confinement regime at high beta(N) values due to a changed behavior of the neoclassical tearing modes. , 2001, Physical review letters.

[3]  J. C. Wiley,et al.  LETTER: The role of rotation in tokamak internal transport barriers , 1997 .

[4]  W. Houlberg,et al.  Bootstrap current and neoclassical transport in tokamaks of arbitrary collisionality and aspect ratio , 1997 .

[5]  E. D. Fredrickson,et al.  Improved confinement with reversed magnetic shear in TFTR. , 1995 .

[6]  P. Diamond,et al.  Neoclassical poloidal and toroidal rotation in tokamaks , 1991 .

[7]  H. Zohm,et al.  LETTER TO THE EDITOR: Collisionality dependence of the neoclassical tearing mode in ASDEX Upgrade , 1999 .

[8]  Ulrich Stroth,et al.  Characterization of the angular momentum transport in ASDEX , 1991 .

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

[10]  Patrick J. McCarthy,et al.  Stationary H-Mode Discharges with Internal Transport Barrier on ASDEX Upgrade , 1999 .

[11]  W. Treutterer,et al.  Performance, heating and current drive scenarios of ASDEX Upgrade advanced tokamak discharges , 2001 .

[12]  F. X. Söldner,et al.  Shear optimization experiments with current profile control on JET , 1997 .

[13]  A. Taroni,et al.  Transport properties and predictive modelling of JET H-mode and optimized shear discharges , 1998 .

[14]  H. Shirai,et al.  Internal transport barrier with improved confinement in the JT-60U tokamak , 1996 .

[15]  Atsushi Fukuyama,et al.  Self-sustained turbulence and H-mode confinement in toroidal plasmas , 1993 .

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

[17]  Patrick J. McCarthy,et al.  Stationary advanced scenarios with internal transport barrier on ASDEX Upgrade , 1999 .

[18]  S. Wolfe,et al.  A new look at density limits in tokamaks , 1988 .

[19]  Lao,et al.  Enhanced confinement and stability in DIII-D discharges with reversed magnetic shear. , 1995, Physical review letters.

[20]  R. J. Hawryluk,et al.  Neoclassical conductivity of a tokamak plasma , 1977 .

[21]  P. McCarthy,et al.  Steady state H mode and Te ~ Ti operation with internal transport barriers in ASDEX Upgrade , 2000 .