Speaker
Description
Topic: TH
Type: Oral synopsis
A full-discharge tokamak flight simulator
E. Fable, F. Janky, O. Kudlacek, M. Englberger, R. Schramm, W. Treutterer, C. Angioni, F. Palermo, M.
Siccinio, H. Zohm, and the ASDEX Upgrade Team
Max-Planck-Institut für Plasmaphysik, Boltzmannstrasse 2, 85748 Garching bei München, Germany
e-mail: emf@ipp.mpg.de
Operation of a plasma discharge in a tokamak requires simultaneous integration of actuators and
diagnostics for plasma control, and physics insight into the type of plasma scenario that is going to be
performed. In view of the initial ITER operation, considering that a pulse has to be operated in the most
secure way possible to avoid loosing the discharge (with associated costs) or even worse, ending in a
disruption, one needs a tool capable of predicting the full discharge beforehand, only using the pulse
schedule plus machine conditions as available information. Such a software could be called “flight
simulator” because it would effectively simulate the real system in its entirety, allowing the pulse
operator to correct errors or optimize the discharge parameters before running the discharge.
This tool should include sufficiently realistic plasma models typical of the tokamak burning plasma,
integrated inside the real control system and its actuators (heating, fueling, magnetic control) with
simplified models. Moreover, it must not depend on shot-specific parameters that are only diagnosed
after the shot has been performed, or it would loose predictive power.
This tool has been obtained for the first time at ASDEX Upgrade, integrating the 1.5D transport-
equilibrium solver ASTRA+SPIDER [1,2], inside the ASDEX Upgrade plasma control system in
SimulinkTM [3]. This integrated package is called Fenix [4,5]. In this contribution, Fenix is presented,
detailing the physics content and demonstrating the several capabilities. Plasma non-linearities are
integrated in a fast simulation framework including control actuators and their realistic behavior. Fenix
reads the pulse schedule of ASDEX Upgrade and predicts the full behavior of the plasma-control
system. From the plasma physics side, the core plasma inside nested flux surfaces is modeled with 1D
transport equations for heat, particles, momentum, and poloidal flux on a 2D quasi-statically evolving
magnetic equilibrium. Reduced models for neoclassical, turbulent transport, MHD activity and heating/
fueling deposition are employed. For the SOL/divertor open-field lines region, simplified 0.5D models
are used which nevertheless contain non-linearities that are observed experimentally (detachment,
dependence of neutral fluxes on gas puff, etc). The magnetic equilibrium is computed in a dynamical
way using the free-boundary solver SPIDER including vacuum vessel currents, yet SOL currents are
not accounted for.
All the pieces of the flight simulator work in concert to reproduce a real plasma with particular focus
on the physics interactions among the elements and how these affect the interpretation and prediction of
experiments. The most critical aspects of the entire system are the links between the elements outside
of the plasma (plasma facing components, gas valves) and the plasma. The problem of heat flux
exhaust and of plasma fueling are some of the most complex in tokamak plasma physics and require a
combination of physics insight and empirical evidence to obtain a rather complete model applicable to
the real plasma.
Moreover, machine conditions can affect the execution of a discharge. It is discussed how this can be
taken into consideration in such a flight simulator. Another aspect which has strong impact on the
simulation result is the non-linear interaction between plasma confinement and equilibrium evolution.
An example is the effect of edge instabilities (ELMs) in determining the average edge current and thus
the X-point angle, and the average pedestal height which determines the global plasma pressure and
equilibrium displacement (Shafranov shift). Or the core transport, usually dominated by
microturbulence, would tailor the profiles peaking which is important for discharge performance
optimization (for example in view of a burning plasma). Still elusive is a complete theory of the L-H
transition which is included in the model in different ways, starting from a more global criterion (check
on power crossing the separatrix), down to a more heuristic local model (comparing the local radial
electric field). The consequences that the choice of the model has on the simulations are discussed.
Finally, it is shown how the simulation comprehensively predicts several types of scenarios and it is
compared to discharges not yet performed (discharge forecast). Examples of the application of the
flight simulator Fenix to a future reactor prototype (EU-DEMO) are also shown.
Acknowledgments: This work has been carried out within the framework of the EUROfusion Consortium and has received
funding from the Euratom research and training program 2014-2018 and 2019-2020 under grant agreement No 633053. The
views and opinions expressed herein do not necessarily reflect those of the European Commission.
[1] E Fable et al 2013 Plasma Phys. Control. Fusion 55 124028
[2] Ivanov A A et al 2005 32nd EPS Conf. on Plasma Physics vol 29C (ECA) P-5.063
[3] Copyright of MathworksTM
[4] F. Janky et al., Fus. Eng. And Design Volume 146, Part B, September 2019, Pages 1926-1929
[5] F. Janky et al., Validation of the Fenix ASDEX Upgrade flight simulator. Talk presented at 12th IAEA Technical Meeting
on Control, Data Acquisition and Remote Participation for Fusion Research (CODAC 2019). Daejeon. 2019-05-13 – 2019-
05-17 (2019)
| Affiliation | Max-Planck-Institut für Plasmaphysik |
|---|---|
| Country or International Organization | Germany |
