Divertor power load investigations with deuterium and tritium in type-I ELMy H-mode plasmas in JET with the ITER-like wall

Abstract

Divertor power load is a major challenge towards a burning plasma in a next-step tokamak. Here, the first results of a divertor power load characterisation in tritium plasmas in type-I ELMy H-mode, obtained in the JET deuterium-tritium campaign (DTE2) performed in 2021, are presented. It is demonstrated that both, transient loads due to type-I ELMs as well as the power fall-off length, do not exhibit an explicit ion mass dependence, with remarkably similar values in the tritium plasmas and in the deuterium references. This gives an improved credence to published scaling law predictions, solely based on deuterium plasma experiments. Moreover, the type-I ELM impact on the inner divertor target is studied in deuterium discharges. A slightly increased parallel energy fluence on the inner target with a factor of 1.08 compared to the outer target is observed. This is explained by the smaller major radius of the inner target.

Exploring the physics of a high-performance H-mode scenario with small ELMs at low collisionality in JET with Be/W wall

“…The divertor heat fluxes in JET are derived from infra-red (IR) thermography using a high-resolution IR camera looking vertically at the divertor target plates [43]. Details on how the ELM energy fluence is evaluated can be found in [44]. For the analysis shown here, we focus on the IR measurements on the outer strike point.…”

“…We find that, in this case, the ELM energy fluence for the discharge with small ELMs is reduced by a factor of ≈3.5 compared to the reference discharge with type I ELMs. To put those results into context, the figure also includes points of a dataset of ELMy H-mode deuterium plasmas from a recent experiment in JET [44], built using dedicated power and gas scans for a range of plasma current (I p = 1.7-2.4 MA) and toroidal magnetic field (B T = 1.7-2.8 T) values. The data shown are the result of averaging the measurements over a selected time window with constant pedestal parameters.…”

“…type III ELM or any reduction of ELM loads due to a different method is not covered by this model. As described in [44], similarly to the original dataset used to build up the model, the majority of the type I ELMy H-mode data points fall within the lower (1:1) and upper (3:1) model boundaries. We note that the model prediction was built for a dataset with T i,ped = T e,ped and therefore it does not account for situations with T i,ped > T e,ped , as it is the case of the 'no-gas' BSE regime.…”

“…(a) ELM energy fluence evaluated in the outer divertor vs. ELM energy loss and (b) parallel ELM energy fluence vs. model predictions[45] for two of the discharges shown in figure5: #94442 (small ELMs, 'no-gas' BSE, red symbol) and #96333 (type I ELMs, green symbol). Those are compared with a database consisting of deuterium fuelled type I ELMy H-mode discharges (grey symbols) from a recent experiment in JET[44]. As can be seen in (b), the majority of the type I ELM data points fall within the boundaries of the lower (1:1) and upper (3:1) model boundaries.…”