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Description
The Divertor Test Tokamak facility (DTT) is designed to investigate power exhaust in fusion reactor-relevant conditions. The schedule of the different operational phases foresees an increase in the installed auxiliary power up to the final full power level. In the very early phase A, the standard single Null (A-SN) plasma scenario is defined by reduced parameters: $B_T=3T$, $I_p=2MA$, and $P_{aux}=P_{ECRH}=8MW$. In the A-SN, the H-mode transport is supposed to be achieved in an integrated scenario taking into account both the core plasma target performances and acceptable Scrape Off Layer (SOL) and divertor conditions. On one hand, the threshold on the power crossing the separatrix to operate in H-mode is an increasing function of the average density: a low density value is thus preferable by considering the limited available auxiliary power. On the other hand, the outboard separatrix density value, and in turn the line average density, is determined by the achievement of the roll-over point to get a partially detached divertor plasma.
In this contribution, the analysis of the SOL is presented to assess the compatibility of a partially detached divertor plasma with H-mode confinement in the DTT Scenario A-SN. The study is carried out using the SOLPS-ITER code suite with a pure D plasma. The transport coefficients are set by considering the power decay length obtained according to the methodology presented in [1]. A density scan has been performed to estimate the roll-over density. In the simplest case without drifts, the inner target is characterized by the most demanding conditions in terms of peak target temperature, due to the location of the stagnation point, quite close to the outer target. The inclusion of drift strongly affects this behaviour, leading to a drop in the electron temperature on the inner plate. Indeed, the Bx∇B drift point downward, with a particle flux from the outer to the inner divertor and a change in the stagnation point position towards the outboard midplane. The roll-over is obtained at $f_{GW}=0.9$ on both targets, corresponding to $n_{e,sep,omp}$=5$\times 10^{19}\;m^{-3}$. By considering the scaling for metallic tokamak[2], the threshold power to enter the H-mode confinement is approximately $P_{LH}=6MW$. Therefore, an operational space can be found to operate DTT in H-mode with partially detached plasma conditions in the early first phase, but with a quite narrow window.
[1]L.Balbinot,Nucl.Mat.En, 34(2023)101350
[2]E. Delabie et al, Status of TC-26: l-H/H-L scaling in the presence of metallic walls ITPA Meeting September 2017