Development of a Synthetic Lithium Beam Diagnostic for the HESEL Turbulence Code and Application to Blob Transport

摘要

Introduction Filamentary structures in the scrape-off layer (SOL) of fusion devices (so called blobs) are expelled from the main plasma and may lead to enhanced erosion at wall components [1]. In order to measure the blob propagation characteristics, Lithium Beam Emission Spectroscopy (Li-BES) can be used in the plasma edge [2]. An improved understanding of blob dynamics can be obtained by comparing a radiative-collisional Li-BES model (SIMULA) [3] combined with a 2D turbulence code (HESEL) [4] constituting a synthetic Li-BES diagnostic. HESEL is a selfcontained, energy conserving model, derived from Braginskii's equations, and covers an area including the last closed flux surface (LCFS) and the SOL. A snapshot of a HESEL density output is shown in Figure la (Density Case), where the plane is spanned by the radial (vertical) and the poloidal (horizontal) axis. The other three images show different synthetic 2D-Li-BES emission signals for the density data in Figure la. The beam is injected from the top (χ= 0cm refers to LCFS). Figure lb shows the resulting emission intensity from the Li_(2p) line (Emission Case). The smearing because of the finite lifetime (≈ 27 ns) of the Li_(2p) energy level leads to a larger structure than in the Density Case [2]. Figure 1c averages over 0.5 x 1.2 cm~2 areas, as this is the approximate covered area by a detector element of the ASDEX Upgrade Li-BES system [5]. Figure Id (Real SNR Block Case) is the same average, but with artificial noise added. The blob is still visible at x ≈ 5 cm, y ≈ 3 cm.