Review and present status of the TEXTOR radiative improved (RI) mode

From 1990, the boronized TEXTOR tokamak was characterized by an improved confinement (coined the 'I mode') at high power that was substantially better than the L mode, but densities had to be limited to n̄_e0/n_GR ≲ 0.5-0.6, where n_GR is the Greenwald density limit. With the injection of Ne, Si or Ar in order to increase the edge radiation and provided that γ = P_rad/P_tot ≳ 0.5, P_NBI-co/P_tot ≳ 0.25 and n̄_e0/n_GR ≳ 0.75, a further improved confinement called the radiative improved mode (RI mode) was discovered in 1993 on TEXTOR, a tokamak of intermediate size, and confirmed on TEXTOR-94. The radiated power fraction γ can reach 0.9, and the radiation is nearly isotropically distributed over the torus wall. The RI mode is characterized by its ability to obtain simultaneously and stationarily high densities and high confinement. It is linked to a substantial lowering of edge n_e, T_e and T_i, a reduction in particle transport and a peaking of the density profile. The RI-mode confinement scales on TEXTOR as τ_E = (n̄_e0/n_GR)τ_ITERH93-P and values up to n̄_e0/n_GR ≈ 1.2 are obtained. There is no detrimental concentration of the seeded impurity at the centre of the plasma. Results of three different interpretative and modelling approaches are in agreement with the improved confinement features; the preliminary indications are that ITG turbulence is strongly reduced. The Z mode observed on ISX-B has a clear resemblance to the RI mode. The very favourable features of the RI mode justify efforts in trying to establish it on larger machines to verify if the present scaling then holds.