J. Doncel

Overview of TJ-II flexible heliac results

The TJ-II is a four period, low magnetic shear stellarator, with high degree of configuration flexibility (rotational transform from 0.9 to 2.5) which has been operating in Madrid since 1998 (R = 1.5 m, a 0.22 m, B0 = 1T , PECRH600 kW, PNBI3 MW under installation). This paper reviews the main technical aspects of the TJ-II heliac as well as the principal physics results obtained in the most recent TJ-II experimental campaign carried out in 2000.

Thermographic calorimetry of the neutral beam injectors heating beams at TJ-II

A new beam diagnostic based on infrared thermography has been developed for the neutral beam injectors of the stellarator TJ-II. A highly anisotropic movable target intercepts the beam at its entrance into the stellarator. The thermal print of the beam is captured with a high resolution infrared camera. The infrared images of the target can be translated, with the appropriate analysis, into power density patterns of the beam. The system is calibrated in situ with two thermocouples adiabatically mounted in the target. The two-dimensional beam power density distribution can be accurately characterized allowing beam optimization with respect to the different parameters involved in the beam formation and transport.

Final Assembly and Present Status of the Spanish Stellarator TJ-II

Publisher Summary The Spanish Stellarator TJ-II is a highly flexible, medium-size fusion device of the heliac-type. This device allows experiments in a large variety of magnetic field configurations to be carried out. The rotational transform can be varied from 0.9 to 2.5. Shear variation is possible upto 10%. The average major plasma radius is 1.5m. The minor dimensions of the bean-shaped plasma are approximately 0.4m by 0.2m. The TJ-II assembly is characterized by its complicated geometry, its narrow tolerances, the small clearances between components and the high geometrical precision required. A total time of about one and a half years is required for the assembly of TJ-II. This is well within the expected period of time. The envisaged tolerances, though very tight, can be met. The computer-based theodolite system has successfully been used for the dimensional control of TJ-II.

Transport Properties in the TJ‐II Flexible Heliac

TJ‐II flexibility is exploited to perform an investigation on the transport properties of this device. Rotational transform can be varied in a wide range, which allows one to introduce low order rationals and to study their effect on transport. On the other hand, confinement properties can be studied at very different rotational transform values and for different values of magnetic shear: Experiments on influence of the magnetic shear on confinement are reported. Plasma potential profiles have been recently measured in some configurations up to the plasma core with the Heavy Ion Beam Probe (HIBP) diagnostic and the electric field values measured in low‐density plasmas are consistent with neoclassical calculations near the plasma core. Plasma edge turbulent transport has been studied in configurations that are marginally stable due to decreased magnetic well. Results show a dynamical coupling between gradients and turbulent transport.

Vandellos: A European site for ITER

On April 17/sup th/ 2002, Spanish Government formally offered the Vandellos site as a possible European ITER site. In this work main technical site specific characteristics of the site are compared with generic requirements. It is shown that Vandellos site offers a number of technical advantages over the reference design mainly in relation with the geotechnical and seismic assumptions as well as in relation with heat sink, electrical supply and heavy transport topics.