1 - Nuclear Sciences and Applications - IAEA

IAEA-CN-50/A-V-3-3 301
TABLE I. COMPARISON OF TJ-I EXPERIMENTAL CONFINEMENT TIMES VERSUS
ALCATOR SCALING AND ROZHANSKITS THEORY RESULTS
BT(T)
1.5
1.0
0.8
Ip(kA)
46
35
37
3. RESULTS OBTAINED
4.9
4.4
3.2
3.0 ± 0.5
1.2 ± 0.1
0.9 ± 0.1
3.1. Central particle confinement measured by laser ablation
The dependence of the central particle confinement time has been measured as
a function of the toroidal magnetic field for discrete values from 0.8 to 1.5 T, at a
fixed line average electron density of (2-3) x 10 13 cnr 3 . Figure 1 shows the results
obtained, the dashed line corresponding to a parabolic dependence. The observed
increase in confinement time is well predicted by the theory of Rozhanskii [2]
(Table I), contrasting with the results obtained at higher toroidal fields in other tokamaks
[3], where the confinement time decreases as the field increases.
We have performed a simple experiment to discover whether the confinement
time of the background particles follows the same trend as the injected impurities in
a toroidal field scan. We kept constant the gas puffing injection rate as we varied B,,
and measured the electron density at the current top in the central plasma region by
Thomson scattering. The rise in density with toroidal field in these conditions is similar
to the rise in TX (Fig. 2), measured in the laser ablation experiment. A similar
rise is observed in radiated power measured by pyroelectric detectors. This discharge
behaviour confirms the improvement in confinement with toroidal field for both
background particles and injected impurities in the TJ-I tokamak for the toroidal field
ranging from 0.8 to 1.5 T.
In Table II, the measured particle confinement times are compared with energy
confinement times at two values of the toroidal field. The latter were deduced by performing
a simplified power balance within the plasma half-radius, by using a onedimensional
static transport code. As is easy to see, the particle confinement time
seems to be linked to the ion energy confinement time and does not correlate with
electron thermal losses.
3.2. Global confinement deduced from fluctuation
The wavenumber/frequency spectra have been estimated for density and potential
fluctuations [4]. The integrated spectra S(kp) and S(w) are shown in Fig. 3. The
TROZ
2.0
1.2
0.8
TALC
3.7
5.7
4.1