Gyrokinetic characterization of the isotope effect in turbulent transport at the FT-2 tokamak

Abstract

Isotope effect allows fusion devices to perform better when heavier hydrogen isotopes are used as fuel, but the reason for this improvement is not yet understood. We present the first direct evidence of the isotope effect on particle confinement in the FT-2 tokamak and investigate it via gyrokinetic simulations. Experimental measurements for comparable hydrogen and deuterium discharges show that the particle confinement time increases by 40% for the heavier isotope species. The isotope effect on particle flux is reproduced in global and local gyrokinetic simulations. Global ELMFIRE simulations demonstrate a systemic reduction in particle fluxes across the radial range, showing a ratio of fluxes H DG G = at the edge and 1.4Local GENE simulations agree qualitatively with the result. Besides the fluctuation level, smaller scales and a favorable shift in the cross-phase between the turbulent fluctuations are found to contribute to the isotope effect in the simulations.

Isotope and fast ions turbulence suppression effects: Consequences for high-β ITER plasmas

“…This may suggest a sub-dominant contribution of Trapped Ion Modes (TIM). This possibility links the results obtained in this paper with other studies in which the role of TEM have been highlighted to create an isotope effect through zonal flows [16,17,18,19]. However, the exact role of these subdominant modes on the isotope effect found in this paper and their interaction with the mechanisms found to play a role is out of the scope of this paper and will be studied in the future.…”

Fast synthetic X-mode Doppler reflectometry diagnostics for the full-f global gyrokinetic modeling of the FT-2 tokamak

“…The particles are initialized according to a prescribed temperature and density profiles taken close to the experimentally measured ones at the low field side of the tokamak, where the trapped electron mode (TEM) typical for FT-2 28 is driven [see Fig. 1(b)].…”

Dependence of the turbulent particle flux on hydrogen isotopes induced by collisionality

“…The understanding of the differences in the properties of transport and confinement of tokamak plasmas when changing the main ion species is a critical component towards the capability of predicting of fusion reactor plasma, where a mixture of deuterium D and tritium T will be used. Many studies have been dedicated to the comparison of the global confinement properties when changing the hydrogen (H) isotope as main ion species [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], with increasing emphasis recently also dedicated to the understanding of changes in the transport properties more than just in the global confinement, also from a theoretical perspective [17][18][19][20]. The observation that the confinement increases with increasing mass of the H isotope is in contraddiction with simple expectations based on an overall gyro-Bohm scaling of local transport, but allows more optimistic expectations when considering the D-T fuel mixture as compared to present experiments which are predominantly performed in D. The recent and the forthcoming campaigns at JET with different H isotopes, including T, have strongly renewed the interest in achieving a deeper understanding of the physics of transport and confinement related to a change of the H isotope as main ion.…”