Isotope effect in transient electron thermal transport property and its impact on the electron internal transport barrier formation in LHD

Abstract

In this study, we perform a comprehensive comparison of the transport hysteresis width in deuterium (D) plasmas, hydrogen (H) plasmas, and D-H mixed plasmas. The core focused modulation electron cyclotron resonance heating (MECH) is applied as the heat source perturbation, and the heat flux is evaluated using the energy conservation equation with the measured electron temperature response and the ECH deposition profile calculated by the raytracing scheme. Systematic density scan in plasmas with different ion mass reveals that there is no significant isotope effect in their hysteresis width. It is found that plasmas with heavier isotope mass can easily form the electron internal transport barrier. As the hysteresis width is insensitive to the isotope mass, the classical part of the diffusivity is considered to be responsible for the isotope effect in the transport barrier formation.

Transient Electron Thermal Transport Analysis Accounting Oblique Electron Cyclotron Resonance Heating Injection to Magnetic Field Line

“…Transport analysis is performed for the dataset of the isotope effect study [14]. Three representative shots having different D/H ratio of 89% (# 146822), 60% (# 147882), and 4% (# 152229) are focused upon.…”

“…Density profile is almost identical for three shots, and characterized by a hollow shape. Peaking of the electron temperature is more visible as the deuterium content increases, likely due to easily formed electron internal transport barrier in deuterium plasmas by an isotope effect [14]. The ECH absorption profiles are calculated by two ray tracing codes, LHDGauss (conventional) and LHDGauss-U (oblique injection accounted) as shown in the second row of Fig.…”

“…In this paper, heat flux evolution shown in [14] is reanalyzed using LHDGauss-U. Although the hysteresis trajectory previously obtained slightly shrinks by up to ∼ 20% where the heating absorption is less significant, qualitative features of the transport hysteresis presented in [14] are preserved. Figure 1 shows the ECH injection configuration on (a) poloidal cross section and (b) top view.…”

“…It is believed that the heat flux in magnetically confined high temperature plasmas cannot be expressed by the simplest "Fick's law", where the heat flux is modeled to be proportional to the local temperature gradient [1]. Instead, a wide variety of models, including the diffusion-convection model [2][3][4][5], the critical gradient model [6,7], nonlocal models [8][9][10][11][12][13][14], models including off-diagonal contribution [15][16][17], and others were developed for comprehensively describing the complicated transport phenomena.…”

“…The new raytracing code author's e-mail: kobayashi.tatsuya@nifs.ac.jp LHDGauss-U accounts for the oblique injection of rays to magnetic field line in the ECH absorption coefficient calculation [21]. In this paper, heat flux evolution shown in [14] is reanalyzed using LHDGauss-U. Although the hysteresis trajectory previously obtained slightly shrinks by up to ∼ 20% where the heating absorption is less significant, qualitative features of the transport hysteresis presented in [14] are preserved.…”