ITER Physics R&D Assessment for Confinement and Plasma Performance Projections

The ranges of confinement-relevant (dimensional and dimensionless) plasma parameters for major tokamaks (JET, JT-60U, TFTR, DIII-D, …) that are expected to contribute to the ITER Physics R&D in the 1990s have been analyzed to characterize confinement and plasma performance in ITER-like designs. We find that the largest tokamaks (JET, JT-60U) should be able to demonstrate H-mode operation (with ELMs, as in ITER) with nτ_ET_i values within an order of magnitude of those required in ITER and have relevant dimensionless plasma parameters (ρ/a, ν*, etc.) within a factor 2 of those in ITER. Extrapolations from dimensionally similar discharges in DIII-D and JET show high-Q/ignition operation in ITER-like plasmas at plasma currents (∼16 MA) well below the nominal (22-MA) design value. Another critical issue for achieving ignition-level plasma performance is the anomalous alpha particle effects, mainly the “toroidal Alfvén eigenmode” (TAE mode). The D-T experiments in TFTR and JET (and simulations using fast beam ions) should realize alpha particle (fast-ion) parameters roughly similar, in relation to TAE mode thresholds, to those projected for ITER. We judge that present-day tokamaks will provide a sufficient database (by the mid-1990s) on H-mode confinement (with ELMs) and possible anomalous alpha particle effects at relevant dimensionless parameters that are expected to be adequate for ITER purposes.