Tokamak COMPASS

Tokamak COMPASS (COMPact ASSembly) is the main experimental facility of our department. It was designed in the eighties in the british Culham Science Centre as a flexible research facility dedicated mostly to plasma physics studies in circular and D shaped plasmas.

The first plasma in COMPASS "broke down" in 1989 in a C-shaped vacuum vessel i.e. in a simpler vessel with a circular cross-section. Pioneering experiments followed, including for example the ITER-relevant tests of magnetic field correction with saddle coils or experiments with non-inductive current drive in plasma.

The operation of tokamak restarted with a D-shaped vacuum vessel in 1992. The operation mode with high plasma confinement (H-mode) was achieved, which represents a reference operation ("standard scenario") for the ITER tokamak. The COMPASS tokamak with its size (major radius 0.6 m and height of the vessel approx. 0.7 m) ranks to smaller tokamaks capable of the H-mode operation. Importantly, due to its size and shape the COMPASS plasmas correspond to one tenth (in the linear scale) of the ITER plasmas. At present, besides COMPASS there are only two operational tokamaks in Europe with ITER-like configuration capable of regime with the high plasma confinement. It is the Joint European Torus JET and the German tokamak ASDEX-U (Institut fuer Plasmaphysik, Garching, Germany). JET is presently the biggest experimental device of this type in the world.

Scale comparison of different tokamaks

Scale of European tokamaks with cross-section similar to ITER


Cutaway diagram of tokamak COMPASS

Cutaway diagram of tokamak COMPASS

In 2002, british scientists started alternative research on larger, spherical tokamak MAST. Operation of COMPASS was discontinued due to insufficient resources for operation of both tokamaks, however, the research programme foreseen for the latter tokamak was not concluded. Due to its important and not completely realised opportunities - and, in particular, due to its direct relevance to the ITER project - the facility was offered for free by the European Commission and UKAEA to the Institute of Plasma Physics AS CR in Prague in autumn 2004. Our Institute has been coordinating research in thermonuclear fusion in the Czech Republic in the framework of EURATOM since 1999. Team of physicists from our institute has a long-time experience in this field of research including operation of a small tokamak CASTOR. The European Commission has also declared that our institute is fully competent to operate the tokamak COMPASS.

Instalation and operation of tokamak COMPASS in the Institute of Plasma Physics AS CR sets the Czech republic among advanced countries in research efforts in high-temperature plasmas and thermonuclear fusion.

Tokamak COMPASS in IPP Prague

Tokamak COMPASS in the Institute of Plasma Physics AS CR


COMPASS vacuum vessel

Internal view of the COMPASS vacuum vessel

Parameters of the tokamak COMPASS

Parameters Current values Expected max. values
Major radius R 0.56 m 0.56 m
Minor radius a 0.18 m 0.23 m
Plasma current Ip (max) 200 kA 350 kA
Magnetic field BT (max) 1.3 T 2.1 T
Vacuum pressure 5x10-8 Pa 1x10-8 Pa
Elongation 1.7 1.8
Plasma shape circular D, SND, elliptical, circular
Pulse length ~ 0.3 s ~ 1 s
Current drive PLH 1.3 GHz 0 MW 0.4 MW
Beam heating PNBI 40 keV 1 x 0.3 MW 2 x 0.3 MW

Physics research programme

  • Role of multi-scale mechanism in the L-H transition
  • Pedestal width physics
  • L-H power threshold and ELM control techniques
  • Hysteresis L-H versus H-L transition
  • Role of atomic physics mechanisms
  • Turbulent structures and intermittency
  • Theory and modelling of edge turbulence
  • Edge Localized Modes
  • Atomic beam probe feasibility study
  • Developments of new techniques for improved data acquisition and analysis

Main systems

  • CODAC (Control, Data Acquisition and Communication) system
  • Power Supply
  • Fast Feedback control system
  • Cooling
  • Vacuum system
  • Fuelling (gas filling system)
  • Hydraulic press system
  • Plasma additional heating system
  • Vessel baking system
  • Glow discharge system

Plasma diagnostic systems

Diagnostics in operation

  • 2 mm interferometer
  • Magnetic diagnostics (approx 400 sensors)
  • Fast camera for visible light
  • 2D spectroscopy
  • Langmuir probes in the divertor
  • Radial reciprocating probe
  • Vertical reciprocating probe

Diagnostics to be installed in 2010-2011

  • Thomson scattering
  • Lithium beam emission spectroscopy
  • Diagnostics of poloidal rotation of plasma impurities
  • Microwave reflectometer for the edge plasma
  • Advanced electric probes on fixed manipulators
Photo of plasma discharge in COMPASS
Photo of plasma discharge in COMPASS

Pictures of plasma in the COMPASS tokamak from the fast visible light camera