The upgraded ASDEX Upgrade contribution to the ITPA confinement database: description and analysis

Abstract

The ITPA multi-machine confinement database has been recently extended, in particular to account for the effect of the metallic plasma facing components installed in the ASDEX Upgrade and JET tokamaks during the last decade. Confinement data from the ASDEX Upgrade tokamak have been contributed to the ITPA confinement database since 1994. The present version, which includes data from 1994 to 2017, is described and discussed in this article. The aim of this work is to document the database before it is made public and report on the main results on the confinement properties reflected in this database. Through the transition from carbon to metallic wall, the operation at low density originally accessible with the carbon wall, has been strongly limited by the occurrence of tungsten accumulation. However, at medium and high densities, the confinement properties with the carbon and metallic walls are rather similar. The database analysis yields in both cases a rather strong plasma current dependence and a clearly negative magnetic field dependence. The density dependence is negligible, while the well-known positive impact of triangularity appears very clearly. These dependences are partly at variance with the widely-used IPB98(y,2) confinement scaling, but in agreement with the analysis of the upgraded ITPA multi-machine and JET databases. The confinement degradation observed at high density with strong gas puffing can be clearly attributed to the density profile in the outer plasma region, as reported in previous studies.