Zeffmeasurements and low-Z impurity transport for NBI and ICRF heated plasmas in JIPP T-IIU

Abstract

A visible bremsstrahlung detector array system for Z_eff measurements and a charge exchange recombination spectroscopy system for fully ionized impurity profile measurements have been installed on JIPP T-IIU to study impurity transport in neutral beam injection (NBI) and ion cyclotron resonance frequency (ICRF) heated plasmas. More impurities are sputtered during ICRF heating than during NBI and/or Ohmic heating. The contribution of carbon to Z_eff is 80-90% for NBI heated plasmas and 60% for NBI + ICRF heated plasmas. With carbon coating of the vacuum vessel, the contribution of carbon to Z_eff becomes 80-90% also for NBI + ICRF heated plasmas. From the radial profile and the time evolution of fully ionized carbon after the ICRF pulse is turned on, a diffusion coefficient D_a of 1.0 m²s⁻¹ and a convective velocity v_a(a) of 13 ms⁻¹ for the carbon impurity at the plasma edge are obtained.