This paper presents a methods for the intrinsic impurity concentration measurements by means of VUV and SXR diagnostics on the JET-ILW tokamak. Measurements of mid-Z impurities content were obtained by means of VUV spectra. To provide absolute concentrations a new relative calibration technique has been proposed. It's based on cross-calibration with calibrated spectrometer by using unresolved transition array of W in the relevant wavelength range. The SXR cameras were used to deduce W profiles and poloidal asymmetries. Focus is given to hybrid discharges stopped by the real-time vessel protection system due to hot-spots formation. This effect was linked to the application of ICRH power. Local D2 gas injection allows mitigating hot-spot formation and run pulses with acceptable temperature values on vessel components. Hot spot temperature analysis showed a lower maximum temperature at higher gas rate. A decrease of impurity concentration with D2 injection rate was observed. Changes in the plasma current have a strong impact on the plasma-wall interaction, both via modifications in the edge density and in the fast-ion losses. Finally it was observed that at constant gas injection rate, both the hot spot temperature and the core impurity content decrease with the separatrix density.
Analysis of metalic impurity content by means of VUV and SXR diagnostics in the presence of ICRF induced hot-spot on the JET-ILW poloidal limiter
VALISA Marco;
2018
Abstract
This paper presents a methods for the intrinsic impurity concentration measurements by means of VUV and SXR diagnostics on the JET-ILW tokamak. Measurements of mid-Z impurities content were obtained by means of VUV spectra. To provide absolute concentrations a new relative calibration technique has been proposed. It's based on cross-calibration with calibrated spectrometer by using unresolved transition array of W in the relevant wavelength range. The SXR cameras were used to deduce W profiles and poloidal asymmetries. Focus is given to hybrid discharges stopped by the real-time vessel protection system due to hot-spots formation. This effect was linked to the application of ICRH power. Local D2 gas injection allows mitigating hot-spot formation and run pulses with acceptable temperature values on vessel components. Hot spot temperature analysis showed a lower maximum temperature at higher gas rate. A decrease of impurity concentration with D2 injection rate was observed. Changes in the plasma current have a strong impact on the plasma-wall interaction, both via modifications in the edge density and in the fast-ion losses. Finally it was observed that at constant gas injection rate, both the hot spot temperature and the core impurity content decrease with the separatrix density.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
