TJ-II

The TJ-II Project

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 f\"ur PlasmaPhysik at Garching (IPP, Germany). The TJII 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. 60% of the investments reverted back to Spanish companies.

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. In order to heat the plasma of TJ-II, the following heating systems are used: microwave heating at the electron cyclotron frequency (ECH, 400 kW), as well as the injection of beams of neutral hydrogen (NBI, up to 4 MW). The TJ-II discharges last 0.5 s and have a repetition frequency of about 5 minutes. The control and data acquisition systems were designed end developed at CIEMAT. The objective of the experimental program of TJ-II is to investigate the physics of a device with a helical magnetic axis with a great flexibility in its magnetic configurations.