Abstract. Detachment of high power discharges is obtained in ASDEX Upgrade by simultaneous feedback control of core radiation and divertor radiation or thermoelectric currents by the injection of radiating impurities. So far 2/3 of the ITER normalized heatflux P sep /R= 15 MW/m has been obtained in ASDEX Upgrade under partially detached conditions with a peak target heatflux well below 10 MW/m 2 . When the detachment is further pronounced towards lower peak heatflux at the target, substantial changes in ELM behaviour, density and radiation distribution occur. The time-averaged peak heat flux at both divertor targets can be reduced below 2 MW/m 2 , which offers an attractive DEMO divertor scenario with potential for simpler and cheaper technical solutions. Generally, pronounced detachment leads to a pedestal and core density rise by about 20-40 %, moderate ( 20 %) confinement degradation and a reduction of ELM size. For AUG conditions, some operational challenges occur, like the density cut-off limit for X-2 ECRH heating, which is used for central tungsten control. Partial detachment of high power discharges in ASDEX Upgrade2

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Alpha particles with energies on the order of megaelectronvolts will be the main source of plasma heating in future magnetic confinement fusion reactors. Instead of heating fuel ions, most of the energy of alpha particles is transferred to electrons in the plasma. Furthermore, alpha particles can also excite Alfvénic instabilities, which were previously considered to be detrimental to the performance of the fusion device. Here we report improved thermal ion confinement in the presence of megaelectronvolts ions and strong fast ion-driven Alfvénic instabilities in recent experiments on the Joint European Torus. Detailed transport analysis of these experiments reveals turbulence suppression through a complex multi-scale mechanism that generates large-scale zonal flows. This holds promise for more economical operation of fusion reactors with dominant alpha particle heating and ultimately cheaper fusion electricity.

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.

Articles you may be interested inData processing and analysis of the imaging Thomson scattering diagnostic system on HT-7 tokamak Rev. Sci. Instrum. 84, 053502 (2013); 10.1063/1.4804161 High-resolution Thomson scattering system on the COMPASS tokamak: Evaluation of plasma parameters and error analysisa) Rev. Sci. Instrum. 83, 10E350 (2012); 10.1063/1.4743956 Conceptual design of new polychromator on Thomson scattering system to measure Zeff a) Rev. Sci. Instrum. 83, 10E334 (2012); 10.1063/1.4733737Design and implementation of a full profile sub-cm ruby laser based Thomson scattering system for MAST Rev.The maximum temperature expected in ITER is in the region of 40 keV and the minimum average density of approximately 3 ϫ 10 19 m −3 is also expected. The proven capability, convenience, and port occupancy of the LIDAR Thomson scattering approach, demonstrated on JET, makes it an excellent candidate for ITER. Nonetheless, there are formidable design challenges in realizing such a diagnostic system. The expected high temperature presents its own problem of a very large relativistic blueshift of the scattered spectrum ͑e.g., / 0 ϳ 0.35 for T e = 40 keV͒, impacting on the laser choice and spectrometer/detector system. The combination of coupling high power lasers to the plasma and broadband wavelength detection has been examined in terms of minimizing the operational risk to the overall system, while optimizing the diagnostic performance. Part of the exercise has also included identifying the present critical components, and reducing their impact, e.g., on diagnostic reliability and performance, and attempt to make the design compatible with possible long term developments and operational requirement. Issues such as redundancy of key operational components, e.g., lasers are explored.