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TJ-II Model

TJ-II is a flexible Heliac installed at Spain's National Fusion Laboratory. It is one of Spain's Unique Scientific and Technical Infrastructures. It is currently operational.


TJ-II and the TJ-II Team in 1996

The flexible Heliac TJ-II was designed on the basis of calculations performed by the team of physicists and engineers of CIEMAT, in collaboration with the Oak Ridge National Laboratory (ORNL, USA) and the Institut für PlasmaPhysik at Garching (IPP, Germany). [1], [2]. The TJ-II project received preferential support from Euratom for phase I (Physics) in 1986[3] and for phase II (Engineering) in 1990[4]. The construction of this flexible Heliac was carried out in parts according to its constitutive elements, which were commissioned to various European companies, although 60% of the investments reverted back to Spanish companies.

The first plasma was produced in 1997.[5]


TJ-II is the third magnetic confinement device in a series. In 1983, the device TJ-I was taken into operation. The denomination of this device is due to the abbreviation of "Tokamak de la Junta de Energía Nuclear", this being the former denomination of CIEMAT. The abbreviation was maintained for successive devices for administrative reasons.

In 1994, the torsatron TJ-IU was taken into operation. This was the first magnetic confinement device entirely built in Spain. Currently, TJ-IU is located at the University of Stuttgart in Germany under the name of TJ-K (the 'K' stands for Kiel, its first location in Germany, before arriving in Stuttgart).


TJ-II perspective view

In TJ-II, the magnetic trap is obtained by means of various sets of coils that completely determine the magnetic surfaces before plasma initiation. The toroidal field is created by 32 coils. The three-dimensional twist of the central axis of the configuration is generated by means of two central coils: one circular and one helical. The horizontal position of the plasma is controlled by the vertical field coils. The combined action of these magnetic fields generate bean-shaped magnetic surfaces that guide the particles of the plasma so that they do not collide with the vacuum vessel wall.

TJ-II discharges last around 0.25 s, with a repetition frequency of about 7 minutes.

Parameter Value Unit
Major radius, R0: 1.5 m
Minor radius, a: < 0.22 m
Plasma volume, V: 1 m3
Field periods: 4
TF coils: 32
Number of ports: 104
Rotational transform, ι/2π: 0.9 - 2.5
Magnetic field on axis, B0: ~1 T
ECRH heating power, PECRH: < 600 kW
NBI heating power, PNBI: < 2 MW
Pulse length: < 200 ms

Goals and Research

The objective of the experimental program of TJ-II is to investigate the physics of a device with a helical magnetic axis having a great flexibility in its magnetic configuration, and to contribute to the international effort regarding the study of magnetic confinement devices for fusion.

Also refer to LNF:Plasma Physics.


Heating and fuelling

In order to fuel and heat the TJ-II plasma, the following systems are used:

Control and data acquisition

The Control and data acquisition systems were designed end developed at CIEMAT.


TJ-II in 2012; front left: Thomson Scattering; left and bottom right: NBI; top: the inclined structures are two HIBP systems. Also visible on top, up front, is the reciprocating Langmuir Probe.

TJ-II is fitted with an extensive set of diagnostic systems installed in its 96 access ports. For information on the magnetic coordinate system (required for cross-diagnostic comparisons), see TJ-II magnetic coordinates.

Passive diagnostics

Active diagnostics

Interactive on-line data visualization

Numerical resources

Simulation codes

Data analysis

  • Wave_ana - Linear and non-linear data analysis, spectral analysis using Fourier and Wavelets
  • EBITA - Tomographic reconstruction
  • Tomography - Tomographic reconstruction based on mode decomposition in flux surface geometry

Software tools


  1. T.C. Hender et al, Studies of a flexible heliac configuration, Report ORNL/TM-10374 (1987) OSTI ID: 6007697
  2. A. Perea et al., "Physics Issues in the Design of TJ-II, Proc. 12th European Conf. Controlled Fusion and Plasma Physics, Budapest, Hungary, 1985, ECA Vol. 9F, Part I, p. 433, European Physical Society (1985)
  3. Application for EURATOM preferential support (Phase I) - TJ-II EXPERIMENT, Technical report, Asociación EURATOM/CIEMAT, 1985
  4. Application for EURATOM preferential support (Phase II) - TJ-II EXPERIMENT, Technical report, Asociación EURATOM/CIEMAT, 1989
  5. Special issue of CIEMAT's magazine Vertices commemorating 20 years of experiments (December, 2017)