Plasma detachment in JET Mark I divertor experiments

Abstract

The experimental characteristics of divertor detachment in the JET tokamak with the Mark I pumped divertor are presented for Ohmic, L-mode and ELMy H-mode experiments with the main emphasis on discharges with deuterium fuelling only. The range over which divertor detachment is observed for the various regimes as well as the influence of divertor configuration, direction of the toroidal field, divertor target material and active pumping on detachment will be described. The observed detachment characteristics such as the existence of a considerable electron pressure drop along the field lines in the scrape-off layer, and the compatibility of the decrease in plasma flux to the divertor plate with the observed increase of neutral pressure and the D α emission from the divertor region will be examined in the light of existing results from analytical and numerical models for plasma detachment. Finally, a method to evaluate the degree and window of detachment is proposed and all the observations of the JET Mark I divertor experiments summarised in the light of this new quantitative definition of divertor detachment.

Characterization of the fluctuating detachment state in ASDEX Upgrade

“…We use the ratio of the calculated (Φ calc D + ) and measured (Φ meas D + ) ion flux to the target as a marker for the magnitude of detachment [10]. Following the simple Two-Point-Model, TPM, [11], in the conduction limited regime the ion flux reaching the divertor target is proportional to the square of the upstream separatrix density n sep u .…”

The impact of divertor detachment on carbon sources in JET L-mode discharges

“…The degree of detachment DOD [8] provides a normalisation criterion for the increase of the ion flux with upstream plasma density, at constant power flux into the edge plasma, compared with the expected dependence high recycling case (ΓD+ ~ n 2 ). to an almost flat profile with significantly reduced values down to T e < 10eV and n e < 4 ⋅ 10 19 m -3 is depicted in figure 3a.…”

The role of particle sinks and sources in Alcator C-Mod detached divertor discharges

“…The difference between the inferred ion source in detachment and that predicted for attached plasmas indicates that the occurrence of detachment reduces the ion source relative to the attached case. This concept is also known as the 'degree of detachment' 47 . Also shown in this figure is the maximum outer divertor ion source calculated assuming that all the power flowing into the outer divertor ionization region [0 There is a clear correlation between the inferred divertor ion source and the power flowing into the ionization region.…”