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.

A theory of the relaxation dynamics of the radial electric field toward its neoclassical value in the regime of subsonic poloidal rotation is presented. It is shown that the relaxation occurs via damped oscillations on time scales proportional to the ion transit time.

Overview of C-2 field-reversed configuration experiment plasma diagnosticsa) Rev. Sci. Instrum. 85, 11D836 (2014); 10.1063/1.4884616 Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pincha) Rev. Sci. Instrum. 83, 10E302 (2012);A new high performance field reversed configuration operating regime in the C-2 devicea)Conventional field-reversed configurations (FRCs), high-beta, prolate compact toroids embedded in poloidal magnetic fields, face notable stability and confinement concerns. These can be ameliorated by various control techniques, such as introducing a significant fast ion population. Indeed, adding neutral beam injection into the FRC over the past half-decade has contributed to striking improvements in confinement and stability. Further, the addition of electrically biased plasma guns at the ends, magnetic end plugs, and advanced surface conditioning led to dramatic reductions in turbulence-driven losses and greatly improved stability. Together, these enabled the build-up of a well-confined and dominant fast-ion population. Under such conditions, highly reproducible, macroscopically stable hot FRCs (with total plasma temperature of $1 keV) with record lifetimes were achieved. These accomplishments point to the prospect of advanced, beam-driven FRCs as an intriguing path toward fusion reactors. This paper reviews key results and presents context for further interpretation. V C 2015 AIP Publishing LLC. [http://dx.

Fusion reactivity for the pB11 fuel has been reassessed for magnetic confinement devices. This study is based on two factors: new measurements of the fusion reaction cross-sections and an accounting of the kinetic effects that lead to the increase of the number of protons at higher energies (with respect to a pure Maxwellian). The net effect leads to an approximately 30% increase of the fusion yield for the same global plasma parameters compared to the previous assessments.

The author considers how the collisionless detrapping of particles from the magnetic mirrors formed between discrete longitudinal field coils affects the thermal conductivity of trapped ions, . The effect is significant when the distance over which a trapped ion drifts during the time of confinement in a local mirror (ripple well) , becomes comparable with the extent of the zone in which local magnetic mirrors exist, z0∼Nq Rδ (δ is the ripple depth, R the major radius of the torus, q the stability factor, N the number of coils, and ωB the cyclotron frequency). At temperatures for which Δ ≫ Z0, becomes proportional to νi. The range of operating temperatures in a tokamak reactor corresponds to Δ ≲ z0. In this range the value of is 5–30 times lower than the value predicted previously and the dependence .