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On the basis of an analysis of the ITER L-mode energy confinement database, two new scaling expressions for tokamak L-mode energy confinement are proposed, namely a power law scaling and an offset-linear scaling. The analysis indicates that the present multiplicity of scaling expressions for the energy confinement time T E in tokamaks (Goldston, Kaye, Odajima-Shimomura, Rebut-Lallia, etc.) is due both to the lack of variation of a key parameter combination in the database, f s = 0.32 R a" 075 k 0 5 ~ A a O25 k 05 , and to variations in the dependence of r E on the physical parameters among the different tokamaks in the database. By combining multiples of f s and another factor, f q = 1.56 a 2 kB/RI p = q eng /3.2, which partially reflects the tokamak to tokamak variation of the dependence of T E on q and therefore implicitly the dependence of T E on I p and n,., the two proposed confinement scaling expressions can be transformed to forms very close to most of the common scaling expressions. To reduce the multiplicity of the scalings for energy confinement, the database must be improved by adding new data with significant variations in f s , and the physical reasons for the tokamak to tokamak variation of some of the dependences of the energy confinement time on tokamak parameters must be clarified.

The most promising concepts for power and particle control in tokamaks and other fusion experiments rely upon atomic processes to transfer the power and momentum from the edge plasma to the plasma chamber walls. This places a new emphasis on processes at low temperatures (1-200 eV) and high densities (10 20 -10 22 m -3 ). The most important atomic processes are impurity and hydrogen radiation, ionization, excitation, recombination, charge exchange, radiation transport, molecular collisions, and elastic scattering of atoms, molecules and ions. Important new developments have occurred in each of these areas. New calculations for impurity and hydrogen ionization, recombination, and excitation rate coefficients for low temperature plasmas that include collisional radiative effects and multi-configuration interactions indicate that earlier estimates of these rate coefficients for plasmas with low Z impurities such as beryllium are too high in selected regions of interest [1]. Transport effects and charge exchange recombination are also key elements for determining the ionization-recombination balance and radiation losses. Collisional radiative effects for hydrogen are an essential ingredient for understanding and modelling high recycling divertors [2,3]. Since the opacity in a high recycling divertor can be large for many of the strongest lines of recycling hydrogen atoms and low Z impurities, the transport of this radiation determines where the energy is deposited and strongly influences the recombination and ionization rate coefficients [4,5]. Molecular collisions play a large role in recycling and in the energy and particle Shortened PSI Review Paper 6 2 balance at the plasma edge [6]. Charge Exchange and elastic collisions are also important for determining the neutral gas pressure and the transfer of plasma energy and momentum to the chamber walls [7,8]. The best available data for these processes and an assessment of their role in plasma wall interactions are summarized, and the major areas where improved data are needed are reviewed.