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In this study, the integrated transport analysis suite, TASK3D-a, was developed to enhance the physics understanding and accurate discussion of the Large Helical Device (LHD) experiment toward facilitating transport model validation. Steady-state and dynamic (transient) transport analyses of NBI (neutral-beam-injection)-heated LHD plasmas have been greatly facilitated by this suite. This will increase the predictability of the transport properties of LHD plasmas toward reactor-relevant regimes and reactor-scale plasmas., source:https://doi.org/10.1585/pfr.8.2403016, identifier:0000-0001-8856-1483

0000-0001-8856-1483, In this study, the integrated transport analysis suite, TASK3D-a, was developed to enhance the physics understanding and accurate discussion of the Large Helical Device (LHD) experiment toward facilitating transport model validation. Steady-state and dynamic (transient) transport analyses of NBI (neutral-beam-injection)-heated LHD plasmas have been greatly facilitated by this suite. This will increase the predictability of the transport properties of LHD plasmas toward reactor-relevant regimes and reactor-scale plasmas.

Particle confinement processes are studied in detail on the Large Helical Device (LHD). Diffusion coefficients (D) and convection velocities (V) are estimated from density modulation experiments. The magnetic configuration and collisionality are widely scanned in order to investigate parameter dependences of D and V. To study the effect of the magnetic configuration, magnetic axis positions (Rax) are scanned from 3.5 to 3.9 m. This scan changes the magnetic ripples quite significantly, enabling the effects of neoclassical properties on measured values to be widely elucidated. Dependences of electron temperature (Te) and helically trapped normalized collisionality are examined using the heating power scan of neutral beam injection. It was found that generally larger (or smaller) contributions of neoclassical transport in the core region, where normalized position p < 0.7, resulted in more hollow (or peaked) density profiles. The larger neoclassical contribution was found to be situated at a more outwardly shifted Rax for the same T e and for higher Te or lower v*h at each Rax. However, it is to be noted that R ax = 3.5 m shows different characteristics from these trends, that is, a more peaked density profile at higher Te or lower v *h. The edge (p > 0.7) diffusion and convection are dominated by anomalous processes. Measured edge turbulence shows a possible linkage.

The Grad-Shafranov equation for axisymmetric fusion plasma has been transformed into a boundary integral equation by expanding the inhomogeneous current density term into a set of 'quasi' radial basis functions (RBFs). These quasi RBFs are derived in such a way that a particular solution for the Grad-Shafranov equation will be a simple Gaussian function. Two or three stages of eigenvalue iterations are required together with a nonlinear optimization to update the scaling factor of each quasi RBF It has been found that excellent accuracy of the boundary element solution can be realized with a small number of quasi RBFs when adopting RBF-dependent scaling factors.