Isotope effects on energy, particle transport and turbulence in electron cyclotron resonant heating plasma of the Large Helical Device

Abstract

The positive isotope effects have been found in ECRH plasma of LHD. The global energy confinement time ( E ) in deuterium (D) plasma is 16% better than in hydrogen (H) plasma for the same line averaged density and absorption power. The power balance analyses showed that clear reduction of ion energy transport, while electron energy transport does not change dramatically. The global particle confinement time ( p ) is degraded in D plasma.  p in D plasma is 20% worse than in H plasma for same line averaged density and absorption power. The difference of the density profile was not due to the neutral or impurity sources, but rather was due to the difference of the transport. Ion scale turbulence levels show isotope effects. The core turbulence ( = 0.5 -0.8) level is higher in D plasma than in H plasma in low collisionality regime and is lower in D plasma than in H plasma. Density gradient and collisionality play a role in core turbulence level.

Extended investigations of isotope effects on ECRH plasma in LHD

“…At  h * < 2, both experimental and neoclassical  h * does not show a clear difference between H and D plasma. This is the same as previous results[11]. At  h * >3, although only one single data point is available in D plasma, experimental  e is lower in D plasma than in H plasma.…”

“…Secondly, in H plasma, turbulence level decreases with increase of the  h * at  h * < 4, however, the turbulence level increases at  h * >4. In a separate dataset of D plasma [11], which includes different heating conditions, the turbulence level at  h * >4 increased as well. The normalized n e and P gradient decrease as  h * increases at  h * < 3, then they both increase with  h * at  h * >3 as shown in Fig.…”

“…However, volume integration quantities were difficult to estimate. Thus, only a relative estimate of  P was possible [11]. The estimated  P was 24% worse in D plasma than H plasma.…”

“…The scaling studies for  E and  P were carried out for the dataset in the first deuterium campaign in 2017 [11]. The results showed 16% better  E and 20% degraded  P in D plasma compared with H plasma.…”

“…This can be partly due to the stochastization of closed flux surface due to ECH driven current [6,12]. Scaling of global energy confinement times ( E ) [10,11], global particle confinement times ( P ) [11] and initial results of turbulence characteristics [11] were reported. In the previous report, the reduced electron heat transport was not found from the data set of power balance analyses [11].…”