Integrated core-SOL modelling of fuelling, density control and divertor heat loads for the flat-top phase of the ITER H-mode D-T plasma scenarios

Abstract

The operation of a tokamak designed to test the sustainability of a thermonuclear grade plasma like the International Tokamak Experimental Reactor (ITER) presents several challenges. Among them is the necessity of fuelling the plasma to reach the density required to generate enough fusion power to achieve Q = 10 and, at the same time, to protect the divertor from melting by keeping the power density flux impinging directly onto it below 10 MW m −2. Whether this goal is achievable or not depends on the details of the fuelling scheme, of the atomic species that are injected into the plasma, of the power radiation pattern in the scrape-off layer and in the divertor, of the additional heating schemes and of the transport mechanisms at work in the core and near the edge of the plasma. In this paper we present, for different operational scenarios, the results of an integrated modelling approach to the problem taking into account all the different aspects of it. The tool adopted for our simulation is the JINTRAC suite of codes, which can simulate in an integrated fashion the transport of particles and heat in different regions of the plasma. We show that, by carefully tuning the gas fuelling and impurity seeding, it is indeed possible on ITER to achieve Q = 10 and at the same time maintain the divertor in a safe operational condition. We also investigate the sensitivity of this result to the uncertainties in the modelling assumptions underlying the simulations presented in the paper.

Compatibility of pellet fuelling with ELM suppression by RMPs in the ASDEX Upgrade tokamak

“…The maximum of the density perturbation is located at 𝜌 𝑝𝑜𝑙 ~ 0.9 . This is similar to that expected in ITER [1,21], however the ratio of pellet to plasma particles is about a factor of two larger than expected in ITER for fuelling pellets. Regarding the location of q=m/n resonance, the surface m/n=7/2 is localised at 𝜌 𝑝𝑜𝑙 = 0.96 [19], i. e. at the outer part of the pellet deposition.…”

JINTRAC integrated simulations of ITER scenarios including fuelling and divertor power flux control for H, He and DT plasmas

“…H-mode, our simulations capture this effect as the continuous ELM model determines the H-mode edge transport, which is tuned to stay at the MHD limit once the pressure (α crit ) is high enough. Therefore, the effective edge transport coefficients that extend 5 mm into the SOL in H-mode, scale inversely with I p and thus so will the edge e-folding lengths [24]. These will be similarly affected in L-mode, as in this case the edge transport is dominated by the Bohm contribution, which is inversely proportional to the local magnetic field and thus also to the enclosed plasma current.…”

“…For the simulations presented here we have developed a special version [5,24] of the standard JETTO Bohm-gyro-Bohm transport model tuned to GLF23 [43], by including a collisionality dependent particle pinch, v pinch (ν * ) = f (ν * ) • 0.5Dr/a 2 , where D is the cross-field particle diffusivity, ν * is the normalized electron collisionality and f (ν * ) = min 1, exp(1 − ν * /v th ).The constant v th = 0.04 was obtained by matching GLF23 density predictions to BgB density predictions of ITER plasmas at different current and field. This pinch reproduces the density peaking observed in GLF23 associated with anomalous transport fluxes at low collisionalities.…”

“…Therefore our H-mode access simulations have optimised the fuelling rate and impurity seeding rates to reach a robust Hmode in the minimal amount of time with high fusion gain (Q ∼ 5) and this is then followed by a higher fuelling rate in which the plasma density increases to ∼85%-90% of the Greenwald limit at which Q = 10 is expected to be achieved in ITER. Extensive fuelling optimisation studies for the stationary phases of ITER DT H-modes over a range of plasma currents and toroidal fields are described in [24].…”

Multiple-isotope pellet cycles captured by turbulent transport modelling in the JET tokamak

“…Active research on pellet fuelling focuses on its compatibility with integrated plasma scenario constraints, including control of MagnetoHydroDynamic (MHD) modes such as Edge Localised Modes (ELMs), plasma exhaust, core turbulent transport, and desired isotope composition. Previous integrated tokamak plasma simulation (integrated modelling) including pellets focused on various aspects of the pellet cycle: improved confinement regimes [2,3,4], edge and fuelling requirements [5], the impact of fuelling on divertor heat-loads [6,7] and the extrapolation of pellet penetration and transport [8].…”