Particle confinement and transport in JT-60U

Abstract

Particle confinement and transport have been systematically analyzed for the improved confinement modes in JT-60U. A scaling law for the total number of ions in the main plasma of ELMy H-mode plasmas was proposed for the first time with confinement times of the particles supplied by NBI (center fuelling) and by recycling and gas-puffing (edge fuelling) separately defined. The confinement time increases and decreases with density for center and edge fuelling, respectively. The comparison between the experimental data and the scaling was made for the high βp ELMy H-mode and reversed shear plasmas. The particle confinement was enhanced over the scaling by a factor of about 2 in the reversed shear plasma. The particle diffusivity and convection velocity were also evaluated based on the perturbation technique using modulated helium gas-puffing in ELMy H-mode and reversed shear plasmas. The particle diffusivity and convection velocity were estimated to be 0.4-2 m 2 /s and-5.5 (inward)~+2.5 (outward) m/s for the ELMy H-mode plasma and to be 0.2-2 m 2 /s and-4 (inward)~0 m/s for the reversed shear plasma, respectively. The particle diffusivity was reduced by a factor of 5-6 around the internal transport barrier compared with that in the outside and inside regions in the reversed shear plasma.

Perturbative studies of transport phenomena in fusion devices

“…In perturbative experiments, n He following a gas puff is measured locally with charge exchange spectroscopy, [39,40,41,31,42,23]. The flux-gradient method is generally used, sometimes compared with impurity transport simulations, [40,42].…”

Comparisons of predicted plasma performance in ITER H-mode plasmas with various mixes of external heating

“…The ash transport and recycling also can play important roles in the steady state fusion performance. Profiles of 4 He transport coefficients have been measured in TFTR DD and DT plasmas [22], and in JT-60U H-mode plasmas [23] with the results that the He velocity pinch profile is inward at most radii. It would be detrimental for ITER performance if a large inward pinch V ash were found, unless a sufficiently large diffusivity D ash were also found.…”

Density modulation experiment to determine transport coefficients on Joint-TEXT Tokamak

“…In addition, the τ p inferred by the density modulation experiment is in good agreement with the result given by Qiming Hu, 18 where the transport coefficients are obtained by fitting measured density with sinusoidal functions. 19 It gives τ p ∼ 26 ms at n 0 ∼ 1.5×10 19 m −3 , but does not consider the particle source term.…”