Space- and time-resolved study of impurities by visible spectroscopy in the high-density regime of JIPP T-II tokamak plasma

Time-resolved spatial profiles of Z eff in JIPP T-II tokamak plasmas have been determined from the measurement of bremsstrahlung in the visible spectral region. The effective ion charge Z eff increases at the plasma centre and decreases at the plasma periphery in the high-electron-density regime. The emissions from low ionization states of light impurities increase notably in the region of lower electron temperatures in this regime. As a result, impurities accumulate in the plasma centre in the high-density regime. The results obtained with respect to the plasma periphery support the interpretation of the behaviour of the impurities, which is based on VUV spectroscopic studies.