Observation of enhanced ion particle transport in mixed H/D isotopes plasma on JET

Observation of enhanced ion particle transport in mixed H/D isotopes plasma on JET

Observation of enhanced ion particle transport in mixed H/D isotopes plasma on JET 150 150 Mathew
UKAEA-CCFE-PR(18)15

Observation of enhanced ion particle transport in mixed H/D isotopes plasma on JET

Particle transport is of a great importance for understanding physics of tokamak plasmas and planning future experiments on larger machines such as ITER. The subject was intensively studied in the past, particularly in relation to density peaking and presence of anomalous inward particle convection in L- and H-mode. While in the L-mode case presence of the anomalous inward pinch was unambiguously demonstrated, particle transport in H-mode was long unclear. Main difficulty of these studies is that particle diffusion and convection could not be measured independently in steady-state condition in presence of a core particle flux. Therefore, it is usually not possible to separate the transport effect – inward convection, from the source effect – slow diffusion of particles introduced to the plasma core by NBI heating. In this work we describe experiments done on JET with mixtures of two hydrogenic isotopes: H and D. It is demonstrated that in case of several ion species, convection and diffusion can be separated in a steady plasma without implementation of perturbative technique such as gas puff modulation. Previous H-mode density peaking studies suggested that for this relatively high electron collisionality plasmas, observed density gradient is mostly driven by particle source and low particle diffusivity D<0.5* χeff. But the transport coefficients derived from observation of the isotope profiles far exceed that value – ion particle diffusion found to be as high as D≥2*χeff, combined with a strong inward convection. Apparent disagreement with previous findings was explained by significantly faster transport of ion components with respect to the electrons, which could not be observed in a single main ion specie plasma. This conclusion is confirmed by quasilinear gyrokinetic simulations.

Collection:
Journals
Journal:
Nuclear Fusion
Publisher:
IOP