First results from divertor operation in Wendelstein 7-X

TLDR

Wendelstein 7‑X, a highly optimized stellarator that began operation in 2015, features a 30 m³ volume, 2.5 T superconducting coils, and up to 10 MW steady‑state heating, designed to demonstrate stellarator advantages near fusion‑power‑plant parameters. The study reports first results from the test divertor installed during the second operation phase in late 2017 and examines how higher‑density operation affects divertor performance and global confinement. With the divertor and new fueling systems, higher‑density hydrogen and helium operation was achieved, leading to detachment at high densities and the highest fusion triple product recorded for a stellarator.

Abstract

Wendelstein 7-X is a highly optimized stellarator that went into operation in 2015. With a 30 cubic meter volume, a superconducting coil system operating at 2.5 T, and steady-state heating capability of eventually up to 10 MW, it was built to demonstrate the benefits of optimized stellarators at parameters approaching those of a fusion power plant. We report here on the first results with the test divertor installed, during the second operation phase, which was performed in the second half of 2017. Operation with a divertor, and the addition of several new fueling systems, allowed higher density operation in hydrogen as well as helium. The effects that higher density operation had on both divertor operation and global confinement will be described. In particular, at high densities detachment was observed, and the highest fusion triple product for a stellarator was achieved.