Energy confinement scaling from the international stellarator database

An international stellarator database on global energy confinement is presented. It comprises a total of 859 discharges from the ATF, CHS and Heliotron-E heliotron/torsatrons and the W7-A and W7-AS shearless stellarators. Some design aspects and operation techniques of the different devices are discussed. The data in the database represent electron cyclotron heated (ECH) and neutral beam injection (NBI) heated discharges in the L mode confinement regime. Results from enhanced confinement regimes such as H mode will be reported elsewhere. Regression expressions for the energy confinement time are given for the individual devices, for the subsets of heliotron/torsatrons and shearless stellarators and for the combined dataset. The combined scaling ISS-95 is found to describe satisfactorily a large tokamak L mode dataset. The aspects of comparing stellarator and tokamak data are discussed on the basis of various scaling expressions. In order to make this database available to interested colleagues, the structure of the database, which is described in detail, is organized in a similar way as the ITER confinement databases.