ISSN:
1572-9486
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Physik
Notizen:
Abstract On COMPASS-D the profile evolution of electron density, electron temperature, perpendicular electric field, poloidal impurity velocity, and neutral density at the outboard mid-plane has been investigated during ohmic single null diverted (SND) discharges undergoing an L/H, H/L, and another L/H transition. This was achieved using a novel combined diagnostic consisting of thermal helium beam and Doppler spectrometry, sharing the same lines of sight. To generate the transitions first an ELM-free H-mode phase was produced by terminating the gas fuelling. Within this H-mode a stepped gas puff was applied triggering an intermediate L-mode phase followed by a second ELM-free phase. It was found that on COMPASS-D the L/H transition is not preceded by a change in velocity or electric field shear. The maximum electric field shear of ∇Eψ ≈ 2 × 103 kV/m2 develops after the L/H transition around the 95% flux surface. Although the neutral density at the separatrix is of the order n D ≈ 1017m−3 no indication of a local influence could be concluded. However, a correlation between the decay of the shear and the gas puff was observed.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1023/A:1022807931846
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