Investigation of self-organized criticality behavior of edge plasma transport in Torus experiment of technology oriented research Phys. Plasmas 11, 5413 (2004); 10.1063/1.1810160High-resolution x-ray crystal spectrometer/polarimeter at torus experiment for technology oriented research-94Rev.An overview of the results obtained so far for the radiative I-mode regime on the upgraded Torus Experiment for Technology Oriented Research ͑TEXTOR-94͒ ͓Proceedings of the 16th IEEE Symposium on Fusion Engineering ͑Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1995͒, Vol. 1, p. 470͔ is given. This regime is obtained under quasistationary conditions with edge neon seeding in a pumped limiter tokamak with circular cross section. It combines high confinement and high  ͑up to a normalized beta,  n ϭ2͒ with low edge q values ͑down to q a ϭ2.8͒ and high density even above the Greenwald limit together with dominant edge radiative heat exhaust, and therefore shows promise for the future of fusion research. Bulk and edge properties of these discharges are described, and a detailed account is given of the energy and particle confinement and their scaling. Energy confinement scales linearly with density as for the nonsaturated Ohmic Neo-Alcator scaling, but the usual degradation with total power remains. No deleterious effects of the neon seeding on fusion reactivity and plasma stability have been observed.
Application of Ion Bernstein Wave Heating (IBWH) into the Princeton Beta Experiment-Modification (PBX-M) [Phys. Fluids B 2, 1271 (1990)] tokamak stabilizes sawtooth oscillations and generates peaked density profiles. A transport barrier, spatially correlated with the IBWH power deposition profile, is observed in the core of IBWH-assisted neutral beam injection (NBI) discharges. A precursor to the fully developed barrier is seen in the soft x-ray data during edge localized mode (ELM) activity. Sustained IBWH operation is conducive to a regime where the barrier supports large ∇ne, ∇Te, ∇νφ, and ∇Ti, delimiting the confinement zone. This regime is reminiscent of the H(high) mode, but with a confinement zone moved inward. The core region has better than H-mode confinement while the peripheral region is L(low)-mode-like. The peaked profile enhances NBI core deposition and increases nuclear reactivity. An increase in central Ti results from χi reduction (compared to the H mode) and better beam penetration. Bootstrap current fractions of up to 0.32–0.35 locally and 0.28 overall were obtained when an additional NBI burst is applied to this plasma.
The local synergistic behavior of lower hybrid and ion Bernstein waves on the Princeton Beta Experiment-Modified tokamak ͓Phys. Fluids B 2, 1271 ͑1990͔͒ is experimentally studied using a two-dimensional hard x-ray camera. The hard x-ray bremsstrahlung emission from suprathermal electrons, generated with lower hybrid current drive, is enhanced during ion Bernstein wave power injection. This enhancement is observed in limited regions of space, suggesting the formation of localized current channels. The effects on plasma electrons during combined application of these two types of waves are theoretically investigated using a quasilinear model. The numerical code simultaneously solves the three-dimensional (R,Z,⌽) torbidal wave equation for the electric field, in the Wentzel-Kramers-Brillouin-Jeffrey approximation, and the Fokker-Planck equation for the distribution function in two dimensions (v ʈ ,v Ќ) with an added quasilinear diffusion coefficient. The radial profile of the noninductively generated current density, the transmitted power traces, and the total power damping curve are calculated. The beneficial effects of a combined utilization of ion Bernstein and lower hybrid waves on the current drive are emphasized. The numerical results are compared with the experimental observations.
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