Filament transport, warm ions and erosion in ASDEX Upgrade L-modes

Abstract

The dynamics of blob filaments are investigated in the scrape-off layer of ASDEX Upgrade by means of lithium beam emission spectroscopy. A comparison of the measurements in L-mode with a recently developed analytical blob model based on a drift-interchange-Alfvén fluid model indicates an influence of a finite ion temperature on the blob dynamics which has typically been neglected in other blob models. The blob dynamics agree well with the sheath-connected regime at lower plasma densities, and inertial effects play only a minor role. At higher densities, a transition into another regime with large blob amplitudes and increased transport is found. This points to a prominent role of blob transport at higher Greenwald fractions. On the basis of the measured blob properties, the erosion on plasma facing components is estimated. For pure deuterium plasmas, the high ion temperatures of blobs lead to a dominant erosion induced by blobs. However, if an impurity concentration of 1% is taken into account, the blob-induced erosion plays a minor role and background plasma parameters determine the total gross erosion.

The influence of temperature dynamics and dynamic finite ion Larmor radius effects on seeded high amplitude plasma blobs

“…Here, R is the radial distance to the outboard mid-plane and B 0 is the reference magnetic field magnitude. In this simple geometry a more accessible representation of the electron and ion gyrofluid moment (6) and (13) is obtained by expressing the set of equations with the help of Poisson brackets and curvature operators. The slab geometry approximation reduces the curvature operator to (6) and (13) to highlight the highly nonlinear nature of our system:…”

Estimation of the plasma blob occurrence rate

“…However, it has still been unknown or there is no general agreement on how, where and at which rate blobs are generated. The prediction of the blob detection rate f d [12], also called the blob occurrence rate [13] or simply blob frequency [14], as part of the blob duty cycle f d τ b or blob packing fraction is of great use for practical considerations about the blob transport, the SOL width [13,15] and plasma-wall interaction [14,15], since especially the large amplitude events carry the most energy and particles. Whereas the correlation time of the blob τ b ∼ δ b /v b can be related to reasonably well understood quantities, the blob detection rate has to be estimated by experience from devices currently in operation [13][14][15], but not from a predictive formula.…”

The Dynamics of Electrons in Linear Plasma Devices and Its Impact on Plasma Surface Interaction

“…Assuming absence of ELMS, transient effects stemming from micro-turbulence seem unavoidable in fusion reactors. Although transient plasma loads have been simulated by laser irradiation or electron beams [25,22] the effect of turbulence on the sputtering yield and erosion overall is so far investigated theoretically only [26,27,28].…”

“…However, the incomplete theory about probes in magnetic fields and possible plasma perturbations by the probes themselves make the quantitative interpretation difficult. Active optical diagnostics using a local source of radiation by neutral atom beams directed through the plasma edge are called beam emission spectroscopy and have been used in TEXTOR [50], DIII-D [51] or AUG [28,52].…”