1 - Nuclear Sciences and Applications - IAEA

300 ZURRO et al.
FIG. 1. Variation of ion confinement time with toroidal field for constant line averaged
density of (2-3) x 1& S cm' 3 .
The laser ablation technique was used to inject silicon and iron into ohmically
heated TJ-I discharges. Particles were injected into the plasma once the plasma
reached its plateau value. The time behaviour of the injected iron in the hot plasma
core was monitored by a pyroelectric detector and a vacuum ultraviolet monochromator,
both collimated along the central plasma chord. The decay time of the perturbations
in the signature of both detectors was used to deduce the impurity confinement
time. To determine the ion energy confinement time, the central ion temperature was
measured by a charge exchange analyser and by Doppler broadening of lines belonging
to the central impurity ions. Thomson scattering profiles were used to determine
the electron energy confinement times.
A square array of four single Langmuir probes (3x3 mm), placed 4 cm above
the equatorial plane on the outer side of the torus, was used to measure density and
potential fluctuations at the limiter radius. In the TJ-I tokamak, the vacuum chamber
plays the role of a belt limiter. Two adjacent probes were used to measure density
fluctuations, being biased in the ion saturation current range. The other pair oriented
along the poloidal angle was unbiased and was used to monitor potential fluctuations.
The electronic system used has a 300 kHz bandwidth. Data acquisition was accomplished
by using a four channel camac module with an 8 kb memory per channel.
Data were digitized at a 500 kHz sampling rate. Conventional FFT was used for data
analysis.