TJ-II

TJ-II is a flexible Heliac installed at Spain's National Fusion Laboratory. It is currently operational.

History

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). The TJ-II project received preferential support from Euratom for phase I (Physics) in 1986 and for phase II (Engineering) in 1990. 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 1999.

Precedents

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.

Description

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 tree-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.

Goals

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.

Operation

The electric energy required for a TJ-II discharge is obtained from a flywheel generator. The coils are cooled by means of a cooling system.

Heating and fuelling

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

• Electron Cyclotron Resonant Heating (ECH, 2 injection beamlines, 600 kW)
• Neutral Beam Injection (NBI, two injectors, up to 4 MW)
• Gas puff
• Pellet injector

Control and data acquisition

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

Diagnostics

TJ-II is fitted with an extensive set of diagnostic systems. For information on their physical location, see TJ-II Sectors.

• Halpha detectors
• Mirnov coils
• Interferometry
• Reflectometry
• Electron Cyclotron Emission
• Soft X-ray Tomography
• Bolometry
• Heavy Ion Beam Probe
• Langmuir Probes
• Spectroscopy
• Charge exchange spectroscopy
• Thomson Scattering
• Helium Beam
• Fast camera

Numerical resources

Simulation codes

• VMEC - 3D Plasma equilibrium, assuming nested flux surfaces
• PIES - 3D Plasma equilibrium
• ASTRA - Plasma transport
• PROCTR - Plasma transport
• EIRENE
• FAFNER
• CUTIE - Full-tokamak fluid turbulence
• MOCA - Monte Carlo Neoclassical transport code
• Master - 1D Master Equation solver for non-diffusive transport

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
• FM - Density reconstruction for the reflectometer

Research

Some research topics at TJ-II are:

• Transport and the magnetic configuration
• Confinement transitions
• Plasma Wall Interaction