Laser blow-off injected impurity particle confinement times in JET and Tore Supra

Abstract

Impurities are injected into JET and Tore Supra by the laser blow-off ablation technique for a variety of experimental situations. The impurity confinement times τp, which reflect the impurity transport, have been measured by fitting exponential curves to the decays of the central brightnesses. Two databases are built up, including ohmic and L mode discharges, with the aim of determining a τp scaling law common to both devices. Different monomial scaling laws are tested and the best one is chosen on the basis of minimization of the standard deviation of the individual regressions. Moreover, the impurity confinement times are compared with the energy confinement times τE for the same data. The energy confinement times are larger than the impurity confinement times, the average ratio tau E/τp being approximately 2.5