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Core and edge turbulence experiments during the 2018 campaign of W7-X

9 Jul 2018, 10:05

15m

Oral presentation New experiments and diagnostic developments

Speaker

Dr Gavin Weir (Max-Planck-Institute for Plasma Physics)

Description

The optimized stellarator Wendelstein 7-X (W7-X) [1] is designed to have an approximately quasi-isodynamic magnetic configuration and reduced neoclassical transport across the plasma minor radius [2]. Two of the high-level goals of the 2018 experimental campaign of W7-X (OP1.2b) are to achieve high-performance stationary hydrogen discharges and to demonstrate the optimization of W7-X. Assessing the importance of turbulent transport, and experimentally measuring predicted changes in Ion Temperature Gradient (ITG) and Trapped Electron Mode (TEM) driven turbulent transport with quasi-isodynamic optimization are important aspects of the OP1.2b experimental campaign. The collisionless TEM is expected to be stable in a maximum-J, quasi-isodynamic magnetic configuration [3] for a large range of plasma density and electron temperature gradients, 0<η_e<2/3, and the drive for ITG modes is predicted to highly localized in W7-X [4]. W7-X is equipped with multiple plasma density and electron temperature fluctuation diagnostics, including three Doppler reflectometers, a poloidal correlation reflectometer, a radial correlation radiometer and a poloidal correlation radiometer. One of the Doppler reflectometers is equipped with a phased array antenna that can sweep +/-20 degree for density fluctuation k-spectra measurements, while the two other Doppler reflectometers are used for poloidal and zonal flow measurements. In addition to these microwave diagnostics, a soft x-ray tomography diagnostic and a phase contrast imaging diagnostic are also used to measure plasma density fluctuations and their characteristics. In this work, electron temperature and plasma density fluctuation measurements from correlation ECE and reflectometry diagnostics during the first island divertor campaign of W7-X will be summarized (OP1.2a), and an overview of plasma turbulence experiments planned for OP1.2b will be presented. [1] T. Klinger et al. Plasma Phys. Control. Fusion 59, 014018 (2017). [2] J. Nührenberg and R. Zille, Phys. Lett. A 129, 113 (1988). [3] J. H. E. Proll, P. Helander, J. W. Connor, G. G. Plunk, PRL. 108, 245002 (2012). [4] P. Xanthopoulos, PRL 113, 155001 (2014).