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Investigates the correlation among geodesic curvature of magnetic field lines, plasma rotation, and improved confinement regimes in tokamaks. Toroidal magnetic confinement configurations of all the charged particles; Minimization of the neoclassical transport; Reduction of the geodesic curvature.

Presents time-dependent simulations of energy, particle, and momentum transport, which show improved confinement similar to the high mode. Suppression of turbulence by sheared flows; Bifurcation phenomenology; High mode and very high mode profiles.

Focuses on the collective scattering measurements of the DIII-D tokamak complicated by significant toroidal and poloidal plasma rotation. Production of large and inhomogeneous radial electrical fields; Doppler shift the spectra of the scattered radiation; Radial variation of the fluctuation magnitude from independent measurements of the radial electric field profile.

The triggering of rapid small edge localized modes (ELMs) by high frequency pellet injection has been proposed as a method to prevent large naturally occurring ELMs that can erode the ITER plasma facing components (PFCs). Deuterium pellet injection has been used to successfully demonstrate the on-demand triggering of edge localized modes (ELMs) at much higher rates and with much smaller intensity than natural ELMs. The proposed hypothesis for the triggering mechanism of ELMs by pellets is the local pressure perturbation resulting from reheating of the pellet cloud that can exceed the local high-n ballooning mode threshold where the pellet is injected. Nonlinear MHD simulations of the pellet ELM triggering show destabilization of high-n ballooning modes by such a local pressure perturbation. A review of the recent pellet ELM triggering results from ASDEX Upgrade (AUG), DIII-D, and JET reveals that a number of uncertainties about this ELM mitigation technique still remain. These include the heat flux impact pattern on the divertor and wall from pellet triggered and natural ELMs, the necessary pellet size and injection location to reliably trigger ELMs, and the level of fueling to be expected from ELM triggering pellets and synergy with larger fueling pellets. The implications of these issues for pellet ELM mitigation in ITER and its impact on the PFCs are presented along with the design features of the pellet injection system for ITER. [ABSTRACT FROM AUTHOR]

The compatibility of detached radiative divertor operation with a robust H-mode pedestal is examined in DIII-D. A density scan produced low temperature plasmas at the divertor target, T e ⩽ 2 eV, with high radiation leading to a factor of ⩾4 drop in peak divertor heat flux. The cold radiative plasma was confined to the divertor and did not extend across the separatrix in X-point region. A robust H-mode pedestal was maintained with a small degradation in pedestal pressure at the highest densities. The response of the pedestal pressure to increasing density is reproduced by the EPED pedestal model. However, agreement of the EPED model with experiment at high density requires an assumption of reduced diamagnetic stabilization of edge Peeling–Ballooning modes. [ABSTRACT FROM AUTHOR]

Abstract: Large 70Hz Type-I edge localized modes (ELMs) are converted into small 130Hz oscillations using edge resonant magnetic perturbations (RMPs) from a coil with currents ⩽0.4% I p in double null DIII-D plasmas. When the RMP is properly phased with respect to the background field errors, all but a few isolated ELM-like events are suppressed. The impulsive pedestal energy loss ΔE ELM/Δt 1/2 to the scrape-of layer is reduced a factor of ⩾20 relative to the Type-I ELMs and the core confinement is unaffected by the perturbation field. Significant changes in the properties of the ELMs are also observed when edge RMPs are applied to lower single null plasmas but the nature of these changes are much more complex. Both lower single null and double null plasmas are being studied to determine how ELM control techniques based on the application of edge RMPs can be expected to scale to future devices such as ITER. [Copyright &y& Elsevier]

Abstract: H-mode confinement is observed for many energy confinement times without edge localized modes (ELMs) in QH (quiescent high-confinement)-mode discharges in DIII–D. To determine the critical differences between ELMing and QH modes we compared electron temperature (T e), density (n e), and ion temperature (T i), in the pedestal (ped) and scrape-off layer (SOL) for a group of discharges. We also compared the electron pressures P ped, and maximum pressure gradient ∇max P e,ped because of their importance in confinement and stability. Experimental results show that the core line averaged density, median T e,ped, T e,SOL, and T e,ped width, and T i,SOL are nearly the same in QH mode as that during ELMs. The n e,ped (average), n e,ped width, P ped, and ∇max P e,ped are similar to corresponding values in QH mode and at various times between ELMs. However, the median T i,ped is 1.6 times higher in QH mode than during ELMing. [Copyright &y& Elsevier]