Dynamics of the pedestal transport during edge localized mode cycles at ASDEX Upgrade

Abstract

The dynamic behaviour of the ion and electron energy, particle and momentum transport measured during type-I edge localized mode (ELM) cycles at ASDEX Upgrade is presented. Fast measurements of the ion and electron temperature profiles revelead that the ion and electron energy transport recover on different timescales, with the electrons recovering on a slower timescale (Cavedon et al 2017 Plasma Phys. Control. Fusion 59 105007). The dominant mechanism for the additional energy transport in the electron channel that could cause the delay in the electron temperature gradient ( ∇ T e ) recovery is attributed to the depletion of energy caused by the ELM. The local sources and sinks for the electron channel in the steep gradient region are much smaller compared to the energy flux arriving from the pedestal top, indicating that the core plasma may dictate the local dynamics of the ∇ T e recovery during the ELM cycle. A model for the edge momentum transport based on toroidal torque balance that takes into account the existence of poloidal impurity asymmetries has been developed. The analysis of the profile evolution during the ELM cycle shows that the model captures the dynamics of the rotation both before the ELM crash and during the recovery phase.

Neoclassical transport in strong gradient regions of large aspect ratio tokamaks

“…This is consistent with our discussion in § 6.2 and the observation that the energy transport in pedestals reaches significant neoclassical levels only in the middle of a pedestal and not at the top and bottom (Viezzer et al. 2020). If instead we had chosen profiles with a stronger temperature gradient such that , we could have been able to retrieve a growing energy flux throughout the pedestal.…”

“…In pedestals, for example, strong gradients of temperature, density and radial electric field of the order of the inverse ion poloidal gyroradius are observed (Viezzer et al 2013). Moreover, it has been found that the ion energy transport in pedestals is close to the neoclassical level (Viezzer et al 2018). Measurements of H-mode pedestals in Alcator C-Mod (Theiler et al 2014;Churchill et al 2015) and Asdex-Upgrade (Cruz-Zabala et al 2022) have shown poloidal variations of density, electric field and ion temperature that cannot be explained using standard neoclassical theory.…”

“…It is thus desirable to extend neoclassical theory for stronger gradients, and logical to choose the ion poloidal gyroradius as the characteristic scale length. Comparisons of experimental data with standard neoclassical theory (Hinton & Hazeltine 1976) such as the one by Viezzer et al (2018) miss finite poloidal gyroradius effects.…”

Optimization of 3D controlled ELM-free state with recovered global confinement for tokamak fusion plasmas

“…The largely broadened ion pedestal can lead to a stronger response of T i,ped despite the decrease of ion pedestal gradient. In addition, ion pedestal is known to be heavily influenced by neoclassical transport 15,37,38 . Here, neoclassical heat flux by RMPs is roughly proportional to I 2 RMP , and it increases more rapidly with the smaller radial electric field and its gradient 39,40 .…”

“…In addition, the pedestal heat diffusivity does not change much during 7.1-7.7 s, indicating that it is insensitive to the decreasing I RMP . It has been reported that the neoclassical transport effect dominates ion heat transport under RMPs 37,38 . However, this collisional transport strongly depends on the RMP strength.…”