Transition between Isotope-Mixing and Nonmixing States in Hydrogen-Deuterium Mixture Plasmas

The transition between isotope-mixing and nonmixing states in hydrogen-deuterium mixture plasmas is observed in the isotope (hydrogen and deuterium) mixture plasma in the Large Helical Device. In the nonmixing state, the isotope density ratio profile is nonuniform when the beam fueling isotope species differs from the recycling isotope species and the profile varies significantly depending on the ratio of the recycling isotope species, although the electron density profile shape is unchanged. The fast transition from nonmixing state to isotope-mixing state (nearly uniform profile of isotope ion density ratio) is observed associated with the change of electron density profile from peaked to hollow profile by the pellet injection near the plasma periphery. The transition from nonmixing to isotope-mixing state strongly correlates with the increase of turbulence measurements and the transition of turbulence state from TEM to ion temperature gradient is predicted by gyrokinetic simulation.

Figure 1

(a) Radial profiles of electron density and (b),(c),(d) radial profiles of H and D density in the plasma with H-beam fueling for the different line-averaged density and wall recycling isotope ratio of (b) $3.8\times {10}^{19}$ (${\mathrm{\Gamma }}_{\mathrm{H}}/{\mathrm{\Gamma }}_{\mathrm{D}}=0.8$), (c) $3.1\times {10}^{19}$ (${\mathrm{\Gamma }}_{\mathrm{H}}/{\mathrm{\Gamma }}_{\mathrm{D}}=0.5$), and (d) $1.9\times {10}^{19}{\mathrm{m}}^{-3}$ (${\mathrm{\Gamma }}_{\mathrm{H}}/{\mathrm{\Gamma }}_{\mathrm{D}}=0.3$).

Figure 2

Radial profiles of (a) the hydrogen isotope fraction, $n_{\mathrm{H}}/(n_{\mathrm{H}}+n_{\mathrm{D}})$ with H-beam fueling and (b) the deuterium isotope fraction, $n_{\mathrm{D}}/(n_{\mathrm{H}}+n_{\mathrm{D}})$ with D-beam fueling. The isotope fractions of recycling are indicated with arrows at the right $y$ axis.

Figure 3

Radial profiles of hydrogen (H) and deuterium (D) density in the plasma with H-beam fueling before ($\mathrm{\Delta }t<0$) and after ($\mathrm{\Delta }t>0$) (a) hydrogen pellet (No. 142315) and (b) deuterium pellet (No. 142314). The peak of deposition of pellets is located at $r_{\mathrm{eff}}/a_{99}\sim 0.9$.

Figure 4

Radial profiles of the hydrogen isotope fraction, $n_{\mathrm{H}}/(n_{\mathrm{H}}+n_{\mathrm{D}})$ before and after the (a) H pellet (No. 142315) and (b) D pellet (No. 142314).

Figure 5

(a) Density fluctuation spectrum in the nonmixing and isotope-mixing states in Fig. 4 and contour of density fluctuation in the space of the normalized minor radius and phase velocity for (b) the nonmixing state and (c) isotope-mixing state (No. 142315). Radial profiles of the projection of $V_{E\times B}$ to the PCI observation plane are also plotted.

Figure 6

Radial profile of (a) the electron density and (b) the electron and ion temperature before pellet injection (nonmixing state) and after pellet injection (isotope mixing state), and (c) the linear growth rate at $r_{\mathrm{eff}}/a_{99}=0.8$ for the nonmixing and isotope-mixing states calculated with gkv.