Latest experimental results of TJ-II Flexible Heliac

low radiated powers (<20%) are typically achieved under all heating schemes applied. These facts are consistent with the spectroscopic observations (small amount of metallic species) and low values of desorbed Ar [3, 4]. A wall desorption rate proportional to total injected power has been observed, that has limited the operation in He at P< 600 kW. This outgassing rate could not be associated to the change of edge characteristics in the density and power scans (see below), and suggest the presence of direct particle losses to the vessel walls Configurational effects. Magnetic configuration (iota 1.28 ‐ 2.24) and plasma volume (0.6 ‐ 1.1 m 3 ) scans have been investigated. Plasma stored energies (W) up to 1.5 kJ have been measured for electron densities and temperatures up to 1.2 x 10 19 m -3 and 2.0 keV respectively with PECRH 600 kW. The dependence of diamagnetic energy of helium plasmas as a function of rotational transform shows, roughly, two regions, as shown in figure 1 (left). In the low iota range, up to iota(0) 1.6 energy content increases. For higher iota values, energy content shows a decreasing trend, partly due to the confinement deterioration associated with iota=2 and also associated to the decreasing tendency of the plasma volume in the higher iota region. In hydrogen plasmas only the higher iota region has been studied so far. It shows no clear dependence of the rotational transform, as seen in figure 1 (right). The obvious influence of the plasma volume in the energy content for a given magnetic configuration can be subtracted, in first approximation, by normalising to the calculated configuration volume. The result, shown in figure 2, indicates an increasing dependence for helium with iota and a smaller but also positive slope for hydrogen plasmas. [5]. Several data points in the iota range 1.8-2.0 are missing in figure 2. The reason is that no accurate volume values have been calculated due to code convergence problems in the proximity of iota=2.