Description
Turbulence is expected to mitigate impurity accumulation, which can otherwise degrade fusion performance or even trigger plasma collapse due to excessive radiation losses. Electron cyclotron resonance heating (ECRH) plasmas provide conditions that enable the achievement of turbulence-rich regimes. Therefore, the transport of high-Z (Fe) impurities is investigated in ECRH experiments at the Wendelstein 7-X (W7-X) stellarator. This analysis aims to quantify the impurity diffusion coefficient profile using the pySTRAHL transport code, incorporating multi-diagnostic measurements and a Bayesian inference.
For the first time, spatially resolved measurements from the X-ray multi-camera tomography system (XMCTS) and bolometry, charge-state-resolved measurements from the VUV overview spectrometer (HEXOS), and the high-resolution X-ray imaging spectrometer (HRXIS) are combined to observe impurity radiation under the assumptions of one-dimensional transport and non-perturbative impurity injection. Laser blow-off is employed to investigate the temporal evolution of the radiation.
The methodology is first validated using synthetic data and subsequently applied to experimental measurements. Preliminary results from HEXOS, HRXIS, and bolometry indicate a diffusion coefficient profile peaking near the separatrix.