Influence of impurities on ion temperature measurements in the tokamak scrape-off layer by retarding field analysers

Abstract

Abstract. Retarding field analyzers (RFA) are one of the only widely accepted diagnostics for measuring ion temperature i T in the tokamak plasma boundary. Usually a pure, Maxwellian plasma composed of a single fuel ion species of charge Z is assumed, in which case the RFA would measure Z T i / . Incident impurity ion fluxes are neglected. We study the influence of impurity ions on i T inferred from a RFA by simulating measurements in a plasma with several ion species. We show that for typical impurity ion fluxes in the tokamak plasma boundary and in the collisionless limit of the kinetic simulations, the assumption of plasma purity causes i T to be underestimated by as much as ~20%.

Inter‐ELM Ion Transport in the ASDEX Upgrade Far Scrape‐Off Layer

“…[12] and references therein). As was shown in [14], this assumption is valid for typical impurity ion fluxes in the SOL. [6,12,13] and references therein).…”

“…The impurity ions are considered as a small non-perturbing minority and their influence on ion temperature measurements is neglected assuming Z i = 1. As was shown in [14], this assumption is valid for typical impurity ion fluxes in the SOL. It is interesting that T i fil / T i sep ≈ 0.07 at Δr sep = 43 mm in the present experiment is much smaller compared with T i fil / T i sep ≈ 0.65 at Δr sep = 21 mm, obtained for turbulent filaments in an AUG L-mode discharge, applying the same detection threshold for j sat [6].…”

Tungsten erosion by impurities and redeposition: focus on the magnetised sheath

“…Thus computations are made with the assumption of a small impurity concentration (here 0.1%) so that the deuterium background is not disturbed. [21] for D + and Ne 10+ in the case of τ = 1. Velocity is normalized with respect to the sonic speed.…”

“…Figure 3. Parallel velocity distribution at the sheath entrance f ,se obtained at the sheath entrance with the model[21] for D + and Ne 10+ in the case of τ = 1. Velocity is normalized with respect to the sonic speed.…”

Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

“…Kinetic simulations of ion collection by an RFA have been made to investigate the impact of a C +4 impurity fraction ranging from 0% to 100% in an otherwise pure Z = 1 plasma. 11 If Z in Eq. (1) is taken to be that of a pure plasma, a less than 20% error in T i will occur for impurity fractions up to 50%.…”