Confinement and Trasnsport
The transport of plasma thermal energy, particles and angular momentum in ITER and the resulting values of the respective confinement times — especially the energy confinement time — determine the feasibility of obtaining and sustaining the burning plasma conditions needed for the conduct of fusion science experiments and fusion technology development and testing. The expected value of the plasma energy confinement time in ITER — about 4 seconds — determines the plasma size, current and toroidal field strength needed to achieve the ITER mission goals of producing 500 MW of fusion power at a fusion power gain Q = 10. Achievement of 4-s energy confinement time in ITER will constitute a 5-fold improvement in confinement time relative to the times obtained in the largest present tokamaks, and will make ITER the 'next-step' device needed to extend plasma transport and confinement science studies to the low-collisionality (low-nu-star), small ion gyroradius (small rho-star) and high plasma boundary temperature (pedestal temperature) 'reactor-regime' characteristic of a future toroidal fusion reactor. In this regard, ITER will be the first-of-kind research facility capable of conducting definitive experiments — transport and confinement and otherwise — in this presently inaccessible plasma parameter regime.

Physics Basis and Extrapolation to ITER
A great deal of past and present world fusion program effort has gone into understanding the physics basis for energy confinement in tokamaks and similar magnetic confinement systems and in applying this understanding to the design and optimization of tokamak burning plasma experiment and reactor prototype designs. Empirical scaling and non-dimensional similarity scaling extrapolation methods and first-principle microturbulence-based numerical simulation methods have been applied, and the ITER-associated 'physics expert group' process has been responsible for the development of a series of increasingly-refined empirical 'H-mode' tokamak energy confinement scalings that have been used as the basis for selection of the current ITER design parameters. Application of non-dimensional similarity and first-principle modelling methods supports — with certain important caveats, particularly about the key role that the plasma boundary temperature plays in determining overall plasma confinement — the present ITER parameter selection and the likelihood that ITER will be able to achieve its Q = 10 design objective and sustain Q > 5 over a credible range of plasma conditions. These achievements will open unique opportunities to conduct 'reactor-regime' confinement science experiments without need for plasma parameter extrapolation or equivocation about the simultaneity of the plasma conditions.

Advanced Confinement
Positivism about the likelihood of ITER being able to meet or exceed its fusion gain and 'reactor-regime' objectives derives in part from studies in present tokamaks that identify a number of ITER-applicable regimes of 'advanced' plasma operation, wherein local and global energy transport is reduced — owing to reduction in microturbulence — relative to the standard 'ELMy H-mode' design basis assumption. The fusion performance enhancement so obtainable can either be exploited directly, to obtain Q > 10 or likely even ignition (fully-self-heated sustained fusion burn), or can be used as a basis for 'advanced tokamak' steady-state operation modes wherein nominal performance (Q = 5-10) is obtained at a reduced plasma current that is sustainable without the need for continuing inductive current drive. In this regard, ITER will be a unique research facility — with steady-state-qualified superconducting coils and power and particle exhaust — for extending 'advanced tokamak' science and development to the reactor regime and for explicitly demonstrating what many fusion researchers believe is the ultimate inherently steady-state embodiment of a tokamak fusion power reactor.

Recent developments in microtubulence modelling now allow explicit calculation of transport in ITER-like plasma geometry

ITER will allow extension of present
'advanced tokamak' science studies to
a true steady-state burning plasma regime.
Success can yield a full demonstration of
the reactor potential of the tokamak.