The main challenge of integrated tokamak modelling is to take into account the interactions between the various processes.
Among our various projects in this field, two of these interactions are currently under scrutiny:
- The interaction between heavy impurity concentration (in particular W) and the kinetic and current density profiles. W transport is strongly dependent on the peaking of temperature and density profiles. The system is coupled, since high core W concentration causes strong radiation losses, thus affecting the core temperature
- The interaction between magnetic islands (NTMs) and the kinetic and current density profiles. NTM evolution is determined by the current density profile (classical driving term), the kinetic profiles (bootstrap current driving term), and locally applied EC current drive. The system is coupled system, since NTMs short-circuit radial transport, thus affecting the kinetic profiles
For both W transport and NTM evolution, many successful predictions have been achieved for given static plasma conditions. The fully integrated approach, as sketched above, is still a challenge.
Example of Neoclassical Tearing mode (NTM) suppression with local current drive in the TCV tokamak
Upper panel: Electron Cyclotron power (in MW) delivering current drive.
Second panel: location of the magnetic surface where the NTM forms (blue), and location where the CD is deposited (red); the y-axis is such that “0” is the centre of the tokamak, and “ 1” is the edge.
Third panel: simulated width of the NTM, result of integrated modelling of evolution of the kinetic and current density profiles and NTM width.
Last panel: spectrogram of magnetic signals of TCV, where the fingerprint of the NTM is the orange curve at ~3 KHz.
The simulation perfectly predicts the growth and subsequent suppression of the NTM, as the current drive location is swept through the plasma
References
- G.M.D. Hogeweij et al, Impact of W on scenario simulations for ITER”, NF 55 (2015) 063031
- G.M.D. Hogeweij et al, ITER-like current ramps in JET with ILW: experiments, modelling and consequences for ITER, NF 55 (2015) 013009