Tokamak physics

Mission

  • develop an integral understanding of the physics of the burning ITER plasma core, including the fast particles generated by the fusion reactions and the magneto-hydrodynamic (MHD) stability of the plasma
  • develop the physics and technology for Tokamak MHD stability control
  • develop an active MHD feed-back control system for ITER based on Electron Cyclotron Heating and Current Drive
     

Annual report 2011 – Fusion Research - Tokamak Physics

Reseach Programme

The programme of the Tokamak Physics (TP) group is directed at ITER burn control and is carried out in collaboration with the Plasma Diagnostics (PD) group and the Computational Plasma Physics–High Temperature (CPP-HT) group of the FOM-Insitute DIFFER. The focus is on the development of a state-of-the-art MHD controller employing Electron Cyclotron Heating and Current Drive (ECH&CD) as an actuator and Electron Cyclotron Emission as a sensor for feed-back control. This includes theoretical modelling of the controller, experimental work on control diagnostics and the development of high power mm-wave equipment. Experiments are planned on the European Tokamak facilities ASDEX Upgrade, MAST and ToreSupra. In the long term, the group intends to play a key role in ITER plasma scenario development, core parameter control and MHD control, through the technical and scientific development of the ITER Upper Port Launcher (UPL) for MHD control and the subsequent scientific exploitation of the UPL and the Upper Port Viewer (UPV) on ITER.

The programme is funded by the ITER-NL program (2010-2013), supporting the development of high-power mm-wave systems and remote handling, the new FOM program 120 “MHD control in Burning Plasmas” funding the plasma science activities and the development of advanced control schemes, the EFDA goal oriented training (GOT) programme, providing grants for three positions for the development of remote handling and the use of 2D optics for plasma control and the NWO Centre of Excellence, funding the development of electron cyclotron wave physics and technology. 
 

Current activities

The current activities of the group include:

 

 

Highlights

Proof of Principle of MHD feed-back control by Electron Cyclotron Waves 

The proof of principle of the line-of-sight feed-back control system for real-time, autonomous suppression and stabilization of tearing modes in a Tokamak was demonstrated on TEXTOR; see B.A. Hennen et al., Plasma Phys and Contr. Fus.52 (2010) p.20. The system is based on ECE sensing of tearing modes and actuation by a steerable ECW launcher. The fast detection of the m/n = 2/1 tearing modes and the retrieval of their location, rotation frequency and phase allowed set-points to be established for real time alignment of the ECW launcher with the centre of the tearing mode and forward this signal in closed loop to the gyrotron source to modulate the power in sync with the rotation of the instability. 

Prototype development of an MHD controller 

A mock-up of the AUG mm-wave launcher was built in order to characterise its mechanical properties. Data obtained served as input for a simulator used to optimise the launcher. Real time control of the fast diplexer (FADIS) cavity was achieved by an adjustable mirror enabling switching, merging and toggling of the high power mm-wave beams. A continuous high power in-line electron cyclotron emission (ECE) system was designed and built for real-time MHD instability control at AUG. 

Control oriented modelling 

A method for real-time identification of Tokamak crash-periods has been developed based on b-spline wavelets in limit cycles. The method will be applied for saw-tooth instability analysis. A combined Kadomtsev-Porcelli model has been set-up to simulate the saw-tooth cycle. A controller has been defined based on in-line ECE sensing and three actuators; power, heat-current drive efficiency and deposition radius.
The Rutherford equation for magnetic island evolution has been linearised with respect to the control actuator settings on power, heat-current drive efficiency and deposition radius. An extreme seeking algorithm is implemented for control of the island size.  

Optical diagnostics for plasma control 

2D visual data has been employed for optical boundary reconstruction of Tokamak plasmas, yielding a robust plasma boundary, also under conditions where the standard magnetic interpretation is beset by large error bars. Reliable plasma boundary reconstruction is needed for physics interpretation and for real time control of the plasma position and shape. 

Remote Handling 

Remote handling compatibility analyses have been carried out for the ITER Upper Port ECH system, the Equatorial Port ECH system and the Upper Port Charge Exchange Spectroscopy diagnostics system.
A visualisation and simulation facility has been built for the development of remote handling procedures and for remote maintenance in the ITER Hot Cell Facility. A physics engine is used to emulate the forces encountered, which are fed-back into a master station for control
 

Scientific papers 2011-2012

  1. Systematic design of a sawtooth period feedback controller using a Kadomtsev-Porcelli sawtooth model, G. Witvoet et al, among them M.R. de Baar and M. Steinbuch, Nucl. Fusion 51 073024 (2011)
  2. Intermediate Frequency Band Digitized high dynamic range radiometer system for plasma diagnostics and Real-Time Tokamak Control, W. Bongers et al, among them M. R. de Baar, Pieter Nuij, A.P.H.Goede and Bart Hennen, Rev. Sci. Inst. 82, 063508 (2011)
  3. Real time, low latency determination of limit cycle periods, M. van Berkel et al. Fus. Eng. Des, doi:10.1016/j.fusengdes. 2011.07.002, 
  4. Numerical demonstration of injection locking of the sawtooth period by means of modulated EC current drive, G. Witvoet et al. Nucl. Fusion 51 103043 (2011) 
  5. Systematic design of a tearing mode control system, B. Hennen, Accepted for publication in Special Issue Nuclear Fusion (2012)
  6. Performance oriented ST control, G. Witvoet et al., Accepted for publication in Special Issue Nuclear Fusion (2012)
  7. Robust sawtooth period control based on adaptive online optimization, J. Bolder, Accepted for publication in Special Issue Nuclear Fusion (2012)
  8. Non-linear control for stabilisation of small neo-classical tearing modes in ITER, B. Hennen et al. Accepted for publication in Special Issue Nuclear Fusion (2012)
  9. Demonstration of sawtooth period locking with power modulation in TCV plasmas, M. Lauret , Submitted to Nuclear Fusion-letter
  10. Integrated modelling of island growth, stabilization and mode locking: consequences for NTM control on ITER, H. van den Brand et al, submitted to Plasma Physics and Controlled Fusion
  11. A fast, non-iterative flux surface estimation and q-profile reconstruction algorithm for control of plasma profiles, G. Hommen et al. Submitted to Nuclear Fusion
     

Personnel of the Tokamak Physics group

 

Name Position E-mail
Marco de Baar Group leader M [dot] R [dot] deBaar [te] differ [dot] nl
Waldo Bongers Scientist w [dot] a [dot] bongers [te] differ [dot] nl
Ben Elzendoorn Research engineer B [dot] S [dot] Q [dot] Elzendoorn [te] differ [dot] nl
Dennis Ronden Research engineer

D [dot] M [dot] S [dot] Ronden [te] differ [dot] nl

Matthijs van Berkel PhD student m [dot] v [dot] berkel [te] tue [dot] nl
Gilles Hommen PhD student g [dot] hommen [te] tue [dot] nl
Menno Lauret PhD student m [dot] lauret [te] tue [dot] nl
Henri Boessenkool PhD student H [dot] Boessenkool [te] differ [dot] nl