2.1 | Tokamak physics

Division: Fusion Physics
Group leader: M.R. de Baar
Scientists: E. Westerhof, A.P.H. Goede, W.A. Bongers, N. Bertelli, J.W. Blokland
Engineers: B.S.Q. Elzendoorn, M.F. Graswinckel, M.A. van den Berg, J. Buskop, D.M.S. Ronden, D. Thoen
Graduate students: D. De Lazzari, B. Hennen, G. Witvoet
Collaborators: R. Heidinger, D. Strauss (FZ-Karlsruhe), A. Bürger, J.W. Oosterbeek (FZ- Jülich, Germany), A. Bruschi, S. Cirant, A. Moro, G. Ramponi (CNR-Milan), H. Zohm, E. Poli (IPP-Garching), R. Chavan, T. Goodman (CRPP-Lausanne), S.B. Korsholm, S. Kragh Nielsen, F. Meo, S. Michelsen, E. Tsakadze (Risø, Denmark), M. Steinbuch, P. Nuij (TU/e), N. Doelman, F. de Vreede (TNO), P. Woskov (MIT, USA), M.D. Tokman, E.V. Suvorov, L. Lubyako, A.A. Balakin, A.G. Shalashov, Yu. Kryachko (Nizhny Novgorod, Russia), L. Kuznetsova (RRC Kurchatov Institute, Russia)
Funding*: FP-74, EFP, ITER-NL

Research programme
The Tokamak Physics Group has extensive expertise using localised heating (ECRH) and current drive (ECCD) for control of magnetic instabilities in nuclear fusion plasmas. The team is involved in heating and MagnetoHydroDynamic (MHD) studies in the TEXTOR tokamak, and in the development of high performance fusion plasma discharges with tolerable MHD and plasma wall interaction in JET.

Mission
The mission of the group is to develop an integrated understanding of the physics of the burning ITER core, including fast particle effects and MHD, and to develop control schemes for the confinement and MHD stability of the burning plasma core. The group is also involved in R&D tasks associated with the design and construction of the Upper Port ECRH/CD launcher for ITER.

Collaborations
The group interacts closely with the instrumentation development group, the computational plasma physics group and the Magnum-PSI team at Rijnhuizen and Eindhoven University in the fields of mm-wave design for diagnostics, computational physics, plasma-wall interaction, and control. The work for ITER is done within the frame of the ITER-NL consortium (FOM, TNO and NRG) and in cooperation with international partners: CRPP Lausanne, FZ Karlsruhe, CNR Milano, and IPP Garching.

Programme
The present experimental programme focuses on the control of magnetic instabilities (MHD modes) in the fusion plasma. This work is mainly carried out in the TEXTOR tokamak at the Forschungszentrum Jülich in Germany. In TEXTOR, MHD modes can systematically be destabilised for a detailed study of the effect of the ECCD power deposition. An in-transmission line radiometer for Electron Cyclotron Emission measurements (ECE) has been developed to exactly determine the location of the instabilities and the location of the power deposition. The hardware for this project has been constructed and is being installed in TEXTOR. First results of in-transmission line ECE measurements during ECRH of MHD modes were done in fall 2007, showing clear MHD-modes during ECRH operation. Model-based system identification and specific control experiments will allow design of dedicated controllers for suppression and stabilisation of magnetic islands.



Figure 2.1: Evolution of the scattered spectrum of injected high power microwave radiation in the TEXTOR tokamak. This radiation is injected for the purpose of local heating and current generation. The thin horizontal line at the top of the image represents the injected 139.85 GHz waves. It was discovered that during a particular phase of a magnetic island (i.e. a perturbation of the topology of closed, nested magnetic surfaces in the form of a helical island like structure) a very strong scattering of these waves to slightly downshifted frequencies occurs. The colored bands indicate the evolution of the scattered spectrum signals, as the phase of the island is slowly shifted back and forth through the microwave beam. These scattered signals are new science. For a better characterisation of the scattered signal, a dedicated diagnostic was developed. The mechanism of the scattering is still under investigation.

In 2008, the modeling and data acquisition for the feed-back system were set-up, and the mechanical properties of the launcher were determined. In 2009, first measurements with the closed feed-back system are foreseen. 

The Rutherford equation for island evolution under intense ECCD has been modeled. Special emphasis was put on the relative merits of heating and current drive in three typical tokamaks: TEXTOR, ASDEX Upgrade and ITER. The calculations underpin the experimental fact that in TEXTOR, the current drive effect is not important for MHD suppression, although it will be the dominant effect in ITER. The TEXTOR and ASDEX Upgrade calculations will partly be used as input to the system for MHD control. 

The ITER-ECRH upper-port launcher activity is supported by modeling calculations. A new code has been used to perform a systematic study of the quasi-optical effects on the EC power deposition profile. The effects are found to broaden the power deposition profile significantly. This could have profound consequences for the ITER ECRH system. In addition, Fokker-Planck calculations including anomalous radial diffusion were done to establish in detail the properties of the EC driven current density profile for 3 ITER-relevant scenarios. 

In addition, engineers in the Tokamak Physics Group are responsible for the development of remote handling procedures and tools for maintenance of the Upper Port Launcher (UPL) in the ITER Hot Cell, and a conceptual study for an UPL acceptance test facility on the ITER site. A mm-wave design based on Remote Steering is being finalised for the Upper Port Launcher as the agreed fall-back solution for ITER.

* supported by the European Fusion Programme (EFP)