Improvement of q-profile measurement by fast observation of pellet ablation at ASDEX Upgrade
The q-profile measurement presented in this article is based on the observation of pellets injected into the plasma and viewed with a fast-framing camera. The pellets sublimate in the plasma and the ablated material is ionized. The ions move along the magnetic field lines, while an ablation cloud is forming. This ablation cloud contains a small fraction of neutral particles which emit visible light after collisional excitation. It is therefore possible to visualize the magnetic field lines along which the pellet passes. The inclination angle of the magnetic field lines with respect to the torus midplane can be determined from this observation. The results are compared with the inclination angles delivered by an equilibrium code. Further analysis shows that it is not meaningful to determine the q-profile from the data of only the pellet ablation, in the case of an elongated plasma as in ASDEX Upgrade. However, the accuracy of the q-profile determined by an equilibrium code, especially in the plasma center, can be greatly improved by using the pellet measurements as additional input data.
Bibliographic Reference: Article: Review of Scientific Instruments, Vol. 68 (1997) No. 11, pp. 4051-4060
Record Number: 199810240 / Last updated on: 1998-03-09
Original language: en
Available languages: en