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.

Neutral beam heating data from JET have been analysed in detail to determine what proportion of the current is driven non-inductively. It is found that in low density limiter discharges, currents of the order of 0.5 MA are driven, while in H-mode plasmas currents of the order of 0.7 MA are measured. These measured currents are found to be in reasonable agreement with theoretical predictions based on neoclassical models. In low density plasmas the beam driven current is large while the neoclassical bootstrap current dominates H-mode plasmas.

A review of the application of dimensionless parameter scaling techniques to magnetic fusion experiments is presented. Because the methods of this type of analysis are not generally known, a detailed discussion of the basis for these techniques is given, including examples. The primary applications and successes of these methods in magnetic fusion research are in the area of transport of energy and particles across surfaces of constant magnetic flux. The experimental justification for the use of these techniques to describe transport is given, and the applications are reviewed. The two key applications of these techniques, the identification of the underlying physical mechanisms that cause transport and the projection of the transport in future devices from presentday experiments, are extensively discussed. Comparison of the results of dimensionless parameter scaling experiments with the regression analysis of multi-machine databases points to limitations in the databases and the analysis of them as the source of the discrepancies. These discrepancies have significant implications for the design optimization of tokamaks, which are discussed here. Finally, the application of dimensionless parameter scaling techniques to plasma stability, to the boundary region between closed and open field lines and to divertor operation in the open field line region are reviewed and discussed.

Results are presented from a series of dedicated experiments carried out on JET in tritium, DT, deuterium and hydrogen plasmas to determine the dependence of the H mode power threshold on the plasma isotopic mass. The Pthr ∝ Aeff-1 scaling is established over the whole isotopic range. This result makes it possible for a fusion reactor with a 50:50 DT mixture to access the H mode regime with about 20% less power than that needed in a DD mixture. Results on the first systematic measurements of the power necessary for the transition of the plasma to the type I ELM regime, which occurs after the transition to H mode, are also in agreement with the Aeff-1 scaling. For a subset of discharges, measurements of Te and Ti at the top of the profile pedestal have been obtained, indicating a weak influence of the isotopic mass on the critical edge temperature thought to be necessary for the H mode transition.

Two different physical models of the H-mode pedestal are tested against the joint pedestal–core database. The first is a confinement model in which the transport down the steep edge gradient is assumed to be dominated by thermal conduction. The second model is a magnetohydrodynamics (MHD) limit model in which it is assumed that the dominant loss mechanism is by the edge localized modes (ELMs), the pressure gradient being determined by a MHD stability limit. These models are then combined with models for the core and shown to give a good fit to the ELMy H-mode database. The resulting two-term scaling expressions are shown to give very similar predictions for the confinement time, in the next step machines ITER and FIRE, to that of the one-term model IPB98(y,2). The predicted stored energy in the pedestal is 28–50% of the total stored energy.