The role of the source versus the collisionality in predicting a reactor density profile as observed on ASDEX Upgrade discharges

Abstract

The design and optimization of a future tokamak fusion reactor, from the point of view of the plasma performance and output fusion power, requires the understanding of the underlying physics and the validation on present experiments of the theory-based tools used for the predictions. Present experimental efforts are devoted to approach reactor-relevant parameters (collisionality, β, normalized heat fluxes and sources, temperatures ratio) as much as possible. In this work a series of discharges performed on ASDEX Upgrade are presented, where plasma density and auxiliary power levels are scanned to cover a parameter space that moves towards reactor relevant parameters. On this dedicated discharge dataset, a first-principle-based model is then applied for validation. The degree of agreement between code results and experimental measurements is shown and discussed. In cases where discrepancy is found, possible causes are identified. It is shown that the employed modeling tool can predict the overall trend, consistent with more fundamental theoretical considerations, although quantitative extrapolation still has to be performed with care. Key results of this work show that the density peaking is mainly sustained by turbulence, with a minor role for the fueling source, and how this experimental demonstration is important to predict future reactor density profiles. Moreover, the role of electromagnetic effects is also pointed out.

First-principles-based multiple-isotope particle transport modelling at JET

“…In a mixed ITG-TEM regime, the expectation -as also seen in QuaLiKiz standalone studies -is that both ion and electron transport coefficients are large, around 2 • χ ef f , with a relatively weak impact of source on all channels. This is the predicted turbulence regime of reactors, where the combination of dominant electron heating and ion-electron heat exchange lead to Q i ∼ Q e [52] and significant density peaking with no source.…”

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

“…In future reactors the collisionality will be lower and the heating will be dominated by electron heating from fusion-generated alpha particles. The turbulence regime is predicted to be mixed ITG-TEM [44]. It is therefore important to model such a regime to assess the extrapolability of the fast isotope mixing effect to reactor-relevant plasmas.…”

Integrated modeling of ASDEX Upgrade plasmas combining core, pedestal and scrape-off layer physics

“…In parallel, the prediction of the plasma kinetic profiles, including their dynamical evolution, is usually obtained by means of one dimensional (1D) approaches which combine different modules describing plasma transport and sources at various levels of integration. This can imply the coupling of different modules to describe various transport mechanisms and sources [10][11][12][13][14][15][16][17][18][19], while adopting boundary conditions from measurements inside the confined plasma, but also the connection between core and edge, including a description of the pedestal [20][21][22][23][24][25][26][27][28][29]. Today these integrated modeling workflows can rely on increasingly sophisticated theory-based models for turbulent transport, particularly applicable in the core of the confined plasma [30][31][32][33].…”

“…19 e/s], the nitrogen seeding rate Γ N2 [10 19 e/s], the NBI power P NBI [MW] (which represents the fueling provided by the NBI), and (because AUG operates with a cryopump) the pumping speed expressed in relative velocity v pump [%] (1 if operating on liquid helium, 0.5 if on liquid nitrogen, 0.2 if turned off).…”