Study of advanced tokamak performance using the International Tokamak Physics Activity database

In recent years, an international database for advanced tokamak discharges has been constructed with data from ASDEX Upgrade, DIII-D, FT-U, JET, JT-60U, RTP, T-10, TCV, TFTR and Tore Supra. Two advanced scenarios for ITER have been studied with this scalar database: The hybrid scenario, with weak magnetic shear and q0=1-1.5 and a steady-state scenario with reversed magnetic shear and q0 > qmin. In this paper, previous work has been extended in three main areas: (i) The scalar data are now taken as an average over the high performance phase (before only peak values were taken), (ii) the data for the two advanced regimes can now be separated, previous studies combined all the data, and (iii) more data from DIII-D, JET and ASDEX Upgrade have been added to this new set of data for the ITPA database. The analysis in this paper concentrates on the operation space and the performance of advanced scenarios obtained so far. The hybrid scenario achieves stationary operation at high βN ∼3 operating at 50% non-inductive current fraction near the no wall beta limit (βN ∼ 4li). The confinement is improved over conventional H-modes, and increases with Ti0/Te0. The data from hybrid scenario discharges show a strong correlation between the ion temperature in the core and ion temperature at the edge of the plasma. The reversed shear scenario splits into two groups of data, predominantly provided by DIII-D and JET respectively. Stationary operation has been obtained at q95≥ 5, with the maximum performance just in line with ITER requirements for non-inductive operation at Q∼5. However, this seems only possible for discharges showing a strong correlation between the core and edge ion temperature, similar to the hybrid regime. Discharges with strong internal transport barriers, although capable of achieving higher confinement, are limited to βN < 2. Common to the two regimes is operation at ITER relevant ν*, with the whole data set showing high confinement and peaked density profiles in this domain. The extrapolation of the results to lower ρi* is hampered by the lack of sufficient input power for the largest experiments since they cannot access βN ∼ 3 at their maximum toroidal field (e.g. JET). Finally, the analysis presented here also sets the scope for further study and collaboration between experiments worldwide, co-ordinated by the ITPA. (author)