2024 – Neoclassical Ti screening of tungsten in pedestal of hybrid steady-state scenario with grassy ELMs

Neoclassical Ti screening of tungsten in pedestal of hybrid steady-state scenario with grassy ELMs

2024 Research Campaign, Task Force: W Compatible Steady State Scenarios

Purpose of Experiment

The purpose of this experiment is to investigate the ion temperature screening of high-Z impurities in low-collisionality pedestal of Steady-State Hybrid scenario with grassy ELMs. Particularly with the new ITER plans for full tungsten wall, the understanding to tungsten transport is more important than ever. Impurity transport in the edge transport barrier (ETB) of regular H-mode plasmas is expected to be neoclassical , with a significant inward pinch proportional to impurity charge and driven by a negative gradient of ion density. Broad density pedestal observed in grassy elm regime and high ion temperatures, might increase the importance of outward temperature impurity screening, resulting in flt or hollow W density profiles in the pedestal.

Experimental Approach

Pedestal transport will be probed by injection of calcium, argon and tungsten. Calcium and tungsten will be injected by the Laser Blow Off system, while the Argon will be puffed by a fast gas valve. Impurity density evolution will be monitored by a combination of CER diagnostic, SXR cameras and AXUV diode cameras and the measured signals will provide constrains for Bayesian inference of pedestal transport coefficients. Although the measurement of W pedestal profile is the main goal of this experiment, it is also the most difficult. CER lines of W has never been used for density measurement and the W signal can be too weak to draw any conclusions about the pedestal profile shape. The purpose of the Ar and Ca injection is to support the conclusions for tungsten transport or provide a backup option of the W measurement is proven to be impossible.