Comparing the Bulk Radiated Power Efficiency in Carbon and ITER-Like-Wall Environments in JET
We use a parameter br for all plasmas that allows detecting the pollution of the plasma bulk by highly radiative impurities. This parameter is defined as the radiative loss of the mixture of impurities relative to their mean Z2 and was used in the past to characterize the efficiency of radiative mantles in Neon seeded discharges. We show that this parameter, though global, is very sensitive to the presence of highly radiative impurities in the bulk of the discharge. In the carbon environment of JET, the value of br is around 10­40MW.m6, indicating the absence of highly radiative impurities in the plasma. In the ILW machine, the value of br is found to depend on the type of additional heating and confinement state of the plasma. We observe that neutral-beam injection (NBI) introduces little W into the plasma, with a br between 2 and 3 10­40MW.m6. Ion-cyclotron radio-frequency (ICRF) waves yield a br of order 5 in L-mode and 10­39MW.m6 in H-mode when no edge-localized modes (ELMs) are present.