7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Numerical investigation of isotope transport scaling and its relation to L2H
power threshold

A. H. Nielsen1, J. Juul Rasmussen1, E.R. Solano2, V. Naulin1, A. S. Poulsen1, A. Thrysøe1, and JET
contributors*1
Department of Physics, Technical University of Denmark, 2 Laboratorio Nacional de Fusión,
CIEMAT, Madrid, Spain, * See J. Mailloux et al., Nucl. Fusion 62, 042026 (2022) for affiliations
e-mail (speaker): ahnie@fysik.dtu.dk
The influence of hydrogen isotopes and He ions on thetransport out of the confinement region in toroidal
magnetically confined plasmas is investigated byapplying the HESEL model. HESEL is a four-field driftfluid model including generalized vorticity, density,electron, and ion pressure equations and using theBraginskii closure for collisions,[1]-[2]. The model issolved on a 2D domain at the outboard mid-plane of a
Tokamak including both open and closed field lines.
The simulations are performed with parameters from
specific JET shots.
For L-mode hydrogen isotope plasma, it is found that theenergy flux density across the last closed flux surface
decreases with mass number, A, and scales like A-0.8 forthe hydrogen isotopes H (Hydrogen), D (Deuterium),and T (Tritium), see Figure 1. This is consistent withstandard isotope scaling of the energy confinement time.
Correspondingly, the threshold, PLH, for the transition toa high confinement state with strongly suppressedtransport - an L-H-like transition, Figure 2 - is found to
decrease with mass number as A-1.4, Figure 3. This
follows the standard ITPA scaling trend [3] with PLH
decreasing like ~1/A. We have applied an effective mass
approach for mixtures of isotopes, which fits the scalingfrom H to T. For the energy density transport, the relative
contributions of electrons and ions were considered showing that the electron contribution dominates in theL-mode cases, while the ion and electron contributions
are almost equal for the L2H transition phase. The
collisional contributions are negligible for the hydrogenisotopes. Our results compare quantitatively to the L2H
campaign at JET, but we have not been able to reproduce
the non-power-law behavior on A observedexperimentally, [4-5].
The confinement transition is also investigated forHelium, He, plasma - here the threshold for L2H is in thesame range as the threshold for Deuterium plasma atsimilar parameters, however, the collisional transport
now becomes significant and is comparable with theanomalous turbulent transport in the H-mode plasma.
The edge transport barrier, set up by a sheared poloidal
flow, is found to be very similar for all the cases
considered - the hydrogen isotopes and the He plasma,
which is consistent with the radial ion force balance
being independent of ion charge and mass.

[3] Righi et al Nucl. Fusion 39, 309 (1999)[4] E.R. Solano et al 2022 Nucl. Fusion 62 076026[5] G. Birkenmeier et al 2023 Nucl. Fusion 65 054001

References[1] A.H. Nielsen et al, Phys. Letters Section A, 379
3097–3101 (2015)[2] J. Madsen et al, Phys. of Plasmas 23 032306, (2016)

Figure 3 Energy flux density and particle flux density
across the LCFS at L2H as a function of A. Plasma
parameters from JET#90993, for a time just before

Figure 1 Energy flux density and particle flux density as
a function of mass number A. Data points represent time
average values from individual HESEL simulations forvarying A and using plasma parameters fromJET#90993, for a time when the plasma was in L-mode.

Figure 2 HESEL simulation using plasma parametersfrom JET#90993 just before L2H. Parameters areconstant except for the edge ion temperature, which isincreased linearly in time. At t=1.2s the plasmatransforms from L- to H-mode.