Operational conditions and characteristics of ELM-events during H-mode plasmas in the stellarator W7-AS

H-mode operation in the low-shear stellarator W7-AS is achieved for specific plasma

edge topologies characterized by three ‘operational windows’ of the edge rotational transform. An

explanation for this strong influence of the magnetic configuration could be the increase of viscous

damping if rational surfaces and thus island structures occur within the relevant plasma edge layer,

thereby impeding the development of an edge transport barrier. Prior to the final transition to

M. Hirsch et al,  2000 Plasma Phys. Control. Fusion 42 A231

Preprint of article:
Orbit topology in conventional stellarators in the presence of electric fields

Orbits are considered in conventional stellarators (i.e. with helical coils) using Boozer co-ordinates. The
Advanced Toroidal Facility (ATF) in Oak Ridge, Tennessee, will be used as an example to study the effects of its configurational  flexibility on orbit topology. It is shown that the symplectic integration technique yields superior results for single particle orbits. These orbits will be compared with predictions using the J* invariant. J* conservation allows examination and understanding of the global stellarator topology, both with and without radial electric fields.

James A. Rome, Nucl. Fus35, 2 (1995)

Preprint of article: topology.pdf
First results from the implementation of the ITER diagnostic residual gas analyzer prototype at Wendelstein 7-X

Fusion reactors and long pulse fusion experiments heavily depend on a continuous fuel cycle, which requires detailed monitoring of exhaust gases. We have used a diagnostic residual gas analyzer (DRGA) built as a prototype for ITER and integrated it on the most advanced stellarator fusion experiment, Wendelstein 7-X (W7-X). The DRGA was equipped with a sampling tube and assessed for gas time of flight sample response, effects of magnetic field on gas detection and practical aspects of use in a state of the art fusion environment.

G. Schlisio, C. C. Klepper, J. H. Harris, T. M. Biewer, V. R. Winters, U. Wenzel, P. Kornejew, H. Laqua, M. Krychowiak, and W7-X team, Rev. Sci. Instrum. 90, 093501 (2019);

Preprint of article: schlisio_drga_w7x_0.pdf