Pellet Injection and Internal Diffusion Barrier Formation in Large Helical Device

Abstract

A high density internal diffusion barrier has been produced in the intrinsic helical divertor configuration in LHD by optimizing the pellet fueling scenario and magnetic configuration. The internal diffusion barrier easily appears in the outer shifted magnetic configuration in which magneto-hydrodynamic stability properties are considered to be favorable. The attainable central plasma density becomes higher as the magnetic axis shifts outward and the central density exceed 5 × 10²⁰ m^-3. Central pressure exceeds 130 kPa and, therefore, very large Shafranov shift is observed, even at high magnetic field (B_t > 2.54 T).