The Science Program of the TCV Tokamak: Exploring Fusion Reactor and Power Plant Concepts
S. Coda, ..., E. Schuster, et al. (Collaboration Paper)
Nuclear Fusion 55 (2015) 104004 (10pp)
Abstract
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TCV is acquiring a new 1 MW neutral beam and 2 MW additional third-harmonic electron cyclotron resonance heating (ECRH) to expand
its operational range. Its existing shaping and ECRH launching versatility was amply exploited in an eclectic 2013 campaign. A new
sub-ms real-time equilibrium reconstruction code was used in ECRH control of NTMs and in a prototype shape controller. The
detection of visible light from the plasma boundary was also successfully used in a position-control algorithm. A new bang-bang
controller improved stability against vertical displacements. The RAPTOR real-time transport simulator was employed to control the
current density profile using electron cyclotron current drive. Shot-by-shot internal inductance optimization was demonstrated by
iterative learning control of the current reference trace. Systematic studies of suprathermal electrons and ions in the presence
of ECRH were performed. The L-H threshold power was measured to be ~50-75% higher in both H and He than D, to increase with the
length of the outer separatrix, and to be independent of the current ramp rate. Core turbulence was found to decrease from positive
to negative edge triangularity deep into the core. The geodesic acoustic mode was studied with multiple diagnostics, and its
axisymmetry was confirmed by a full toroidal mapping of its magnetic component. A new theory predicting a toroidal rotation
component at the plasma edge, driven by inhomogeneous transport and geodesic curvature, was tested successfully. A new
high-confinement mode (IN-mode) was found with an edge barrier in density but not in temperature. The edge gradients were found
to govern the scaling of confinement with current, power, density and triangularity. The dynamical interplay of confinement and
magnetohydrodynamic modes leading to the density limit in TCV was documented. The heat flux profile decay lengths and heat load
profile on the wall were documented in limited plasmas. In the snowflake (SF) divertor configuration the heat flux profiles were
documented on all four strike points. SF simulations with the EMC3-EIRENE code, including the physics of the secondary separatrix,
underestimate the flux to the secondary strike points, possibly resulting from steady-state ExB drifts. With neon injection,
radiation in a SF was 15% higher than in a conventional divertor. The novel triple-null and X-divertor configurations were also
achieved in TCV.