The science program of the TCV tokamak: exploring fusion reactor and power plant concepts

Abstract

Abstract. TCV is acquiring a new 1 MW neutral beam and 2 MW additional 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 ECCD. Shot-byshot 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% 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 MHD 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 steadystate EB 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 achieved transiently in TCV.

Experimental observations of modes with geodesic acoustic character from the core to the edge in the TCV tokamak

“…The experiments were performed on the TCV tokamak [19,20] at the Swiss Plasma Center, EPFL, Switzerland. The major radius and minor radius are 0.88 m and 0.25 m, respectively.…”

Modification of SOL profiles and fluctuations with line-average density and divertor flux expansion in TCV

“…Within this framework, intense experimental activity has been carried out in the TCV tokamak [22], exploiting the flexibility of this device to test shoulder formation against variation of magnetic geometry. Shoulder formation and blob properties have been investigated in a series of L-Mode density ramps performed at different poloidal flux expansion values, in order to address the role of parallel connection length in the process of SOL profile flattening.…”

Real Time Hybrid Model Predictive Control for the Current Profile of the Tokamak à Configuration Variable (TCV)

“…In parallel, the reference error for the plasma current is the input to the MPC. This block performs the MPC of the plant computed as shown in Equation (10). The computational load within this block is reduced as much as possible, since the controller involves the analytical solution of the minimization for the functional given in Equation (15).…”

“…The main parameters, are major radius 0.88 m, horizontal minor radius 0.25 m, toroidal field at major radius 1.5 T, and plasma current 1MA with elongation up to 2.8 and high triangularity from´0.7 to 1. This uniquely expansive shaping capability extends to limited and diverted plasmas, the latter featuring open divertor geometry and including single-and double-null as well as snowflake topologies [10]. Due to the flexible configuration and control, TCV is a tokamak that is especially active in control research, and all of this invaluable experience is expected to provide important input for safe and effective operation of ITER [11][12][13][14][15][16].…”