A novel code is presented, which is capable of computing the NBI fast-ion distribution in real-time. We discuss the approximations needed to arrive at this goal: A simplified beam geometry is used for calculating the beam attenuation. Finiteorbit-width effects are taken into account by an orbit average of the beam deposition. The time-dependent solution of the Fokker-Planck equation (2D in velocity) is then calculated based on analytic expressions. This code currently takes ≈25 ms per time step, which is roughly a factor of 1000 faster than the more sophisticated NUBEAM code. Nevertheless, good agreement between both codes is found in a comprehensive benchmark.

Abstract.The neutral beam current drive efficiency has been investigated in the ASDEX Upgrade tokamak by replacing on-axis neutral beams with tangential off-axis beams.A clear modification of the radial fast-ion profiles is observed with a fast-ion Dalpha diagnostic that measures centrally peaked profiles during on-axis injection and outwards shifted profiles during off-axis injection. Due to this change of the fast-ion population, a clear modification of the plasma current profile is predicted but not observed by a motional Stark effect diagnostic.The fast-ion transport caused by MHD activity has been studied in low collisionality discharges that exhibit strong (1,1) modes. In particular due to sawtooth crashes, significant radial redistribution of co-rotating fast-ions is observed which can very well be described by the Kadomtsev model. In addition, first tomographic reconstructions of the central 2D fast-ion velocity space in the presence of sawtooth crashes allow the investigation of the pitch dependence of the mode-imposed redistribution: A stronger redistribution of mainly co-rotating fast ions is observed than of those with smaller pitch values.

Recent improvements to the heating and diagnostic systems on the ASDEX Upgrade tokamak allow renewed investigations into non-inductive operation scenarios with improved confinement in a full-metal device. Motivated by this, a scenario with , and a high non-inductive current fraction has been developed. The scenario offers good confinement with and normalised ion temperature gradients . Moreover, it is robust against resistive magnetohydrodynamic (MHD) instabilities, but does suffer from ideal MHD instability when . To verify the understanding of the plasma transport processes, the heat transport was modelled using TGLF. This revealed that electromagnetic effects at high β and/or from fast ions appear to be missing from TGLF’s physics model. As accurate reconstruction of the plasma equilibrium is crucial for studies of advanced scenarios, this publication also documents the presence of polarised background light that can contaminate motional stark effect measurements and thus interfere with equilibrium reconstruction.

The TCV tokamak is augmenting its unique historical capabilities (strong shaping, strong electron heating) with ion heating, additional electron heating compatible with high densities, and variable divertor geometry, in a multifaceted upgrade program designed to broaden its operational range without sacrificing its fundamental flexibility. The TCV program is rooted in a three-pronged approach aimed at ITER support, explorations towards DEMO, and fundamental research. A 1 MW, tangential neutral beam injector (NBI) was recently installed and promptly extended the TCV parameter range, with record ion temperatures and toroidal rotation velocities and measurable neutral-beam current drive. ITER-relevant scenario development has received particular attention, with strategies aimed at maximizing performance through optimized discharge trajectories to avoid MHD instabilities, such as peeling-ballooning and neoclassical tearing modes. Experiments on exhaust physics have focused particularly on detachment, a necessary step to a DEMO reactor, in a comprehensive set of conventional and advanced divertor concepts. The specific theoretical prediction of an enhanced radiation region between the two X-points in the low-field-side snowflake-minus configuration was experimentally confirmed. Fundamental investigations of the power decay length in the scrape-off layer (SOL) are progressing rapidly, again in widely varying configurations and in both D and He plasmas; in particular, the double decay length in L-mode limited plasmas was found to be replaced by a single length at high SOL resistivity. Experiments on disruption mitigation by massive gas injection and electron-cyclotron resonance heating (ECRH) have begun in earnest, in parallel with studies of runaway electron generation and control, in both stable and disruptive conditions; a quiescent runaway beam carrying the entire electrical current appears to develop in some cases. Developments in plasma control have benefited from progress in individual controller design and have evolved steadily towards controller integration, mostly within an environment supervised by a tokamak profile control simulator. TCV has demonstrated effective wall conditioning with ECRH in He in support of the preparations for JT-60SA operation.