Overview of the TCV tokamak program: Scientific progress and facility upgrades

The TCV tokamak is augmenting its unique historical capabilities (strong sh aping, strong electronheating) with ion heating, additional electron heating compatible with high densities, and variable divertorgeometry, in a multifaceted upgrade program desig ned to broaden its operational range without sacrificing itsfundamental 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) wasrecently installed and promptly extended the TCV parameter range, with record ion temperatures and toroidalrotation velocities and measurable neutral-beam current drive. ITER-relevant scenario development has receivedparticular attention, with strategies aimed at maximizing performance through optimized discharge tr ajectoriesto avoid MHD instabilities, such as peeling-ballooning and neoclassical tearing modes. Experiments on exhaustphysics have focused particularly on detachment, a necessary step to a DEMO reactor, in a comprehensive set ofconventional and advanced divertor concepts. The specific theoretical prediction of an enhanced radiation regionbetween 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 par ticular, the double decay length inL-mode limited plasmas was found to be replaced by a single length at high SOL resistivity. Ex periments ondisruption mitigation by massive gas injection and electron-cyclotron resonance heating (ECRH) have begun inearnest, in parallel with studies of runaway electron generation and control, in both stable and disruptive conditions; a quiescent runaway beam carrying the entire electricalcurrent appears to develop in some cases. Developments in plasmacontrol have benefited from progress in individual controller designand have evolved steadily towards controller integration, mostlywithin an environment supervised by a tokamak profile controlsimulator. TCV has demonstrated effective wall conditioning withECRH in He in support of the preparations for JT-60SA operation.