Overview of first Wendelstein 7-X high-performance operation
The optimized superconducting stellarator device Wendelstein 7-X (with major radius R = 5.5 m, minor radius $$a$$ = 0.5 m, and 30 m3 plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of 1–4.5 × 1019 m–3 with central electron temperatures 5–10 keV were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to 1.4 × 1020 m–3 were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of 8 · 1019 m–3 a temperature of 3.4 keV with $$T_e/T_i$$ = 1 was transiently accomplished, which corresponds to $$nT_i(0)τ_E =$$ 6.4 × 1019 keV s m–3 with a peak diamagnetic energy of 1.1 MJ and volume-averaged normalized plasma pressure $$\langleβ\rangle$$ = 1.2%. The routine access to high plasma densities was opened with boronization of the first wall. After boronization, the oxygen impurity content was reduced by a factor of 10, the carbon impurity content by a factor of 5. The reduced (edge) plasma radiation level gives routinely access to higher densities without radiation collapse, e.g. well above 1 × 1020 m–2 line integrated density and $$T_e = T_i =$$ 2 keV central temperatures at moderate ECRH power. Both X2 and O2 mode ECRH schemes were successfully applied. Core turbulence was measured with a phase contrast imaging diagnostic and suppression of turbulence during pellet injection was observed.
- Research Organization:
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
- Sponsoring Organization:
- USDOE; EUROfusion Consortium
- Contributing Organization:
- W7-X Team
- Grant/Contract Number:
- 633053
- OSTI ID:
- 1598166
- Journal Information:
- Nuclear Fusion, Vol. 59, Issue 11; ISSN 0029-5515
- Publisher:
- IOP ScienceCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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