Results from the investigation of neoclassical core transport and the role of the radial electric field profile (E r) in the first operational phase of the Wendelstein 7-X (W7-X) stellarator are presented. In stellarator plasmas, the details of the E r profile are expected to have a strong effect on both the particle and heat fluxes. Investigation of the radial electric field is important in understanding neoclassical transport and in validation of neoclassical calculations. The radial electric field is closely related to the perpendicular plasma flow (u ⊥) through the force balance equation. This allows the radial electric field to be inferred from measurements of the perpendicular flow velocity, which can be measured using the x-ray imaging crystal spectrometer (XICS) and correlation reflectometry diagnostics. Large changes in the perpendicular rotation, on the order of ∆u ⊥ ∼ 5 km/s (∆E r ∼ 12 kV /m), have been observed within a set of experiments where the heating power was stepped down from 2 M W to 0.6 M W. These experiments are examined in detail to explore the relationship between heating power, temperature and density profiles and the radial electric field. Finally the inferred E r profiles are compared to initial neoclassical calculations using measured plasma profiles. The results from several neoclassical codes, sfincs, fortec-3d and dkes, are compared both with each other and the measurements. These comparisons show good agreement, giving confidence in the applicability of the neoclassical calculations to the W7-X configuration.

Abstract. In the first operational phase of the stellarator Wendelstein 7-X (W7-X), the X-ray Imaging Crystal Spectrometer (XICS) system has been commissioned for measuring radial profiles of ion and electron temperature, T i and T e , plasma rotation velocities v P , and selected impurity densities n Z . This paper shows the first measurements of the spectrometer and gives an initial calculation of impurity transport parameters derived from an Ar impurity transport study. Using Bayesian analysis, the temporal evolution of Ar impurity density profiles after an Ar gas puff could be observed with a time resolution of up to 5 ms, yielding a maximum value for the diffusion coefficient of D = 1.5 m 2 /s at ~0.5 and small pinch velocities in the inner plasma region.

The neutral beam deposition model in the BEAMS3D code is validated against neutral beam attenuation data from Wendelstein 7-X (W7-X). A set of experimental discharges where the neutral beam injection system of W7-X was utilized were reconstructed.These discharges scanned the magnetic configurations and plasma densities of W7-X. The equilibrium reconstructions were performed using STELLOPT which calculates three-dimensional self-consistent ideal magnetohydrodynamic equilibria and kinetic profiles. These reconstructions leveraged new capabilities to incorporate electron cyclotron emission and X-ray imaging diagnostics in the STELLOPT code. The reconstructed equilibria and profiles served as inputs for BEAMS3D calculations of neutral beam deposition in W7-X. It is found that if reconstructed kinetic profiles are utilized, good agreement between measured and

In the previous divertor campaign, the Wendelstein 7-X (W7-X) device injected 3.6 MW of neutral beam heating power allowing for the achievement of densities approaching 2 × 10 20 m −3 , and providing the first initial assessment of fast ion confinement in a drift optimized stellarator. The neutral beam injection (NBI) system on W7-X is comprised of two beam boxes with space for four radio frequency sources each. The 3.6 MW of heating reported in this work was achieved with two sources in the NI21 beam box. The effect of combined electron-cyclotron resonance heating (ECRH) and NBI was explored through a series of discharges varying both NBI and ECRH power. Discharges without ECRH saw a linear increase in the line-integrated plasma density, and strong peaking of the core density, over the