TJ-II

Figure 1:Asociación EURATOM-Ciemat (Spain)

The history of TJ-II
TJ-II Parameters
TJ-II Milestones
TJ-II Objectives
TJ-II experimental programme

The history of TJ-II

The flexible heliac TJ-II is the result of calculations performed by the team of physicists and engineers of the "Asociación EURATOM-Ciemat" Spain, in collaboration with the Oak Ridge National Laboratory (ORNL) in the US and the Association EURATOM-Max-Planck-Institute for Plasma Physics (IPP) at Garching (Germany). The TJ-II project received preferential support from EURATOM in 1986 during phase I (Physics) and during phase II (Engineering) in 1990. Following European-wide call for tenders, the construction of the different TJ-II components was performed by companies scattered all around Europe. TJ-II is the main Spanish contribution to the complementary path in the European strategy towards future fusion reactors which investigate the so-called "improved concepts" such as stellarators. In this way - which is parallel to the tokamak concept - advanced technologies and scientific results can be incorporated in ITER and DEMO.

Figure 2:TJ II First Plasma

TJ-II Parameters

Major radius	1.5 m
Average magnetic field	1 T
Number of periods	4
Number of TF coils	32
Rotational transform at magnetic axis	0.96 < iota < 2.5
Range of plasma average radius	0.10 < a < 0.25 m
Shear range	-1 < s < 10 %
Magnetic well depth range	0 < w < 6 %
Plasma heating	- Initially, 1 MW electron cyclotron heating at 53.2 GHz - In a second stage, 4 MW neutral beam injection heating
Plasma temperature	7 - 10 Million degrees centigrade
Plasma density	1.6 x 1019 /m3

Figure 3:TJ-II Support
Structure

Figure 4:TJ-II Cooling
System

Figure 5:TJ-II Vacuum
Vessel

TJ-II Milestones

1983	Initial operation of the tokamak TJ-I.
1986	Creation of the "Asociación EURATOM-Ciemat para Fusión". Basic approval by EURATOM of the scientific viability of the flexible heliac project TJ-II (Phase I).
1990	EURATOM decides financing 45% (preferential support) of the TJ-II project when its technical viability is demonstrated (Phase II).
1994	Initial operation of the TJ-I Upgrade torsatron. This is the first magnetic confinement device entirely constructed in Spain. TJ-IU torsatron was given to the University of Kiel (Germany) in 1999.
1997	Initial operation of the flexible heliac TJ-II.
1998	"Creation of Laboratorio Nacional de Fusión por Confianmiento Magnético": National Laboratory of Magnetic Confinement Fusion in Ciemat.

Figure 6:TJ-II Machine

TJ-II Objectives

The objective of the experimental programme of TJ-II is to investigate the physics of a device with a helical magnetic axis and wide flexibility in its magnetic configuration. The physics problems of magnetically confined plasmas studied are of much interest to the fusion community.
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 generates 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, microwave heating at the electron cyclotron frequency (ECH, 400 kW) will be used, as well as the injection of beams of neutral hydrogen (NBI, up to 4 MW). The TJ-II discharges will last 0.5 s and will occur every 5 minutes. The control systems and the system of data acquisition were designed and developed by Ciemat.
TJ-II will address a complete experimental programme on the physics of helical magnetic axis plasmas. These studies are to be undertaken in three phases. The first phase started in December 1997. Two microwave beams operated at 53.2 GHz and with total injected power of 1 MW are being used. Studies are being carried out on equilibrium windows, effect of high and low order resonances, electron cyclotron (EC) wave-induced electron kinetic processes, and transport.
During the second phase the plasma will be heated using beams of neutral hydrogen atoms that have been previously accelerated to such energies that the final injected power inside the vacuum vessel should be of the order of 3 MW. The following studies will be carried out: finite beta effects on configurations of phase I, instability development by magnetic well removal, and bootstrap current effects.
In the third phase, the added injected power will reach 6 MW. The heating method to be used will depend on the results of the previous phases. Physics issues such as beta-limit and second stability regime access will be addressed:

• effect of rational and non-rational rotational transform values;
• influence of magnetic well, iota profiles, and magnetic axis position on confinement;
• studies of EC wave-induced electron kinetic processes;
• transport in the long mean free path regime;
• finite beta effects on magnetic configurations;
• instability development by magnetic well removal; possible access to second stability regime;
• bootstrap current effects;
• beta limits of heliac configurations.

TJII Experimental programme

Figure 7:Dummy Text