Magnetic configuration effects on the edge heat flux in the limiter plasma on W7-X measured using the infrared camera and the combined probe

Abstract

Controlling the heat and particle fluxes in the plasma edge and on the plasma facing components is important for the safe and effective operation of every magnetically confined fusion device. This was attempted on Wendelstein 7-X in the first operational campaign, with the modification of the magnetic configuration by use of the trim coils and tuning the field coil currents, commonly named iota scan. Ideally, the heat loads on the five limiters are equal. However, they differ between each limiter and are non-uniform, due to the (relatively small) error fields caused by the misalignment of components. It is therefore necessary to study the influence of the configuration changes on the transport of heat and particles in the plasma edge caused by the application of error fields and the change of the magnetic configuration. In this paper the upstream measurements conducted with the combined probe are compared to the downstream measurements with the DIAS infrared camera on the limiter.

Characterization of the W7-X scrape-off layer using reciprocating probes

“…Although this approach cannot be used for quantitative analysis and direct comparisons to divertor loads (since it misses e.g. the ion temperature [34], heat transmission coefficients, and does not account for conductive heat transport), it is a widely used measure for tokamaks [7,35,36]. There, the q profiles typically show an exponential decay in the SOL with a characteristic fall-off length λ q , which is taken as the SOL width:…”

Equilibrium effects on the structure of island divertor and its impact on the divertor heat flux distribution in Wendelstein 7-X

“…It should be noted that the thermal pressure involved in the HINT calculation consists of electron and ion pressure components (which are not dissociable), while only the electron pressure has been measured by the combined probe up to now. If the ratio of T i /T e ≈ 2-4 in the SOL region of W7-X is taken into consideration [51], it could be roughly estimated that the pressure value matches well between the experimental and HINT results. Finally, the fine regulated pressure profiles are applied to HINT calculations, so as to obtain self-consistent equilibrium fields closest to real experiments.…”

Characteristics of the SOL ion-to-electron temperature ratio on the J-TEXT tokamak with different plasma configurations

“…The retarding field analyzer (RFA) probe has been developed and widely used for the measurement of the edge ion temperature profile in many fusion devices such as JET [3,4], Tore Supra [1], Alcator C-mod [5], ISTTOK [6], STOR-M [7,8], EAST [9], LHD [10], W7-X [11] and J-TEXT [12]. A strong dependence of the edge ion-to-electron temperature ratio, τ i/e , on the SOL ion self-collisionality, , has been observed in several tokamak experiments, which is consistent with the simulation results of two-dimensional (2D) edge transport codes, EDGE2D and onion-skin [13].…”

“…However, due to the limited diagnostic methods, the edge ion temperature is generally set to be equal to the electron temperature in many theoretical models. Research during recent decades has found that the ion temperature is not equal to the electron temperature [1,2], especially in the tokamak SOL region, where the ion temperature can be by a factor of 2 or even up to 5 higher than the electron temperature. Therefore, an accurate measurement of the edge ion temperature profile is required for conducting a proper edge plasma transport analysis.…”