First experiments with non-axisymmetric magnetic perturbations, toroidal mode number n = 2, produced by newly installed in-vessel saddle coils in the ASDEX Upgrade tokamak show significant reduction of plasma energy loss and peak divertor power load associated with type-I Edge Localized Modes (ELMs) in high-confinement mode plasmas. ELM mitigation is observed above an edge density threshold and is obtained both with magnetic perturbations that are resonant and not resonant with the edge safety factor profile. Compared with unperturbed type-I ELMy reference plasmas, plasmas with mitigated ELMs show similar confinement, similar plasma density and lower tungsten impurity concentration.

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High spatial resolution radial profiles of the perpendicular plasma rotation velocity u ⊥ using a dual channel 50-75 GHz Doppler reflectometer system on the ASDEX Upgrade tokamak are presented for a variety of discharge scenarios, including Ohmic, L-mode, H-mode, etc with forward and reversed magnetic field and co-and counter neutral beam injection. The reflectometers have steppable launch frequencies f o = c/λ o , with selectable O-or X-mode polarization, giving tokamak edge to mid-radius coverage. Low-field-side antennae (hog-horn antenna pairs) with deliberate tilting (primarily poloidally) produce a Doppler shifted spectrum directly proportional to the perpendicular velocity f D = u ⊥ k ⊥ /2π = u ⊥ 2 sin θ t /λ o . The incident angle θ t between the beam and cut-off layer normal varies with plasma shape, cut-off layer position and refraction. However, typical angles range from 5˚to 27˚giving a probed turbulence wavenumber, k ⊥ , range of 1.8-14.3 cm −1 , with resulting Doppler shifts f D of up to 5 MHz. The measured perpendicular velocity is u ⊥ = v E×B + v phase , which for a typical H-mode is slightly positive in the tokamak scrape-off-layer with a deep negative well across the H-mode steep pressure gradient pedestal region and then following the perpendicularly projected toroidal fluid velocity in the core, should be dominated by the E × B velocity, as the intrinsic phase velocity is predicted to be small, which may allow u ⊥ to be interpreted directly as the radial electric field E r profile.

Local edge parameters on the ASDEX Upgrade tokamak are investigated at the L-mode to H-mode transition, during phases with various types of edge-localized modes (ELMs), and at the density limit. A scaling law for the boundary electron temperature,e,b B 0.8 t I 0.5 p , is found which describes the H-mode threshold for deuterium-puffed discharges with favourable ion ∇B-drift direction. The region of stable operation is bounded by type I ELMs near the ideal ballooning limit and by a minimum temperature necessary to avoid thermal instability of the plasma edge. Stationary operation with type III ELMs imposes an upper limit on the edge temperature. Within the entire range of boundary densities investigated (n e,b 8 × 10 19 m −3 ), both L-mode and H-mode are found to be accessible. During type I ELMy H-mode, a relation of global confinement with the edge pressure gradient is found which is connected with a loss of the favourable density dependence predicted by the ITER-92P and ITER-93H ELMy H-mode scalings. At high density, better confinement is achieved in H-modes with an edge pressure gradient below the ideal ballooning limit, e.g. during type III ELMy H-mode with impurity-seeded radiation.