Recent developments in Helias reactor studies

The Helias ignition experiment is an upgraded version of the Wendelstein 7-X experiment. The magnetic configuration is a 4-period Helias configuration (major radius 18 m, plasma radius 2.0 m, B = 4.5 T), which presents a more compact option than the five period configuration. Main effort has been focussed on two versions of the 4-period configuration: one option is the power reactor HSR4/18 providing at least 3 GW of fusion power and the second option is the ignition experiment HSR 4/18i aiming at a minimum of fusion power and the demonstration of self-sustaining burn. The design criteria of the ignition experiment HSR 4/18i are the following: The experiment should demonstrate: a safe and reliable route to ignition, self-sustained burn without external heating, steady-state operation during several hundred seconds, reliability of the technical components and tritium breeding in a test blanket. The paper discusses the technical issues of the coil system and describes the vacuum vessel and the shielding blanket. The power balance will be modelled with given profiles and the ignition conditions will be investigated using current scaling laws of energy confinement in stellarators. The plasma parameters of the ignition experiment are: peak density 2-3·1020 m-3, peak temperature 11-15 keV, average beta 3.6%, fusion power 1500 - 1700 MW. (author)