RESUMO
Recent neutronics studies of blankets for tokamak-based demonstration fusion neutron source (DEMO-FNS) showed a crucial influence of coolant composition on the transmutation rate of transuranic elements and tritium breeding in the system. The coolant choice varies with the neutron spectrum and shielding properties of the blanket. This paper presents a three-dimensional model developed for the Monte Carlo calculations of DEMO-FNS neutronics. The model was used for estimating the capability of the radiation shield to protect the superconducting electromagnetic system (EMS) from neutrons and gamma radiation for two types of coolants, namely water and supercritical carbon dioxide. The neutron balance, neutron energy spectra, and energy release of the neutrons and gamma radiation were evaluated in the shield, case, and superconductor at the inner and outer contours of the EMS. In comparison with the closed shielding option, the radiation heating power at the case and superconductor of the outer contour located between the injection port (IP) and the blanket maintenance port was 10 times higher than that in the area facing the injector. Thus, further improvement of the local shield design near the IP is needed.
RESUMO
Experimental data on spatial distributions of a pellet cloud electron density are necessary for the development of many applications of pellet injection, namely, plasma fuelling, discharge control, and plasma diagnostics. An improved approach of electron density measurements inside the cloud of a polystyrene pellet ablating in hot plasma of the large helical device is described. Density values of (1-30) × 10(16) cm(-3) depending on the background plasma parameters and distance from the solid pellet were measured.
RESUMO
In the Large Helical Device (LHD), various spectroscopic diagnostics have been applied to study the ablation process of an advanced impurity pellet, tracer-encapsulated solid pellet (TESPEL). The total light emission from the ablation cloud of TESPEL is measured by photomultipliers equipped with individual interference filters, which provide information about the TESPEL penetration depth. The spectra emitted from the TESPEL ablation cloud are measured with a 250 mm Czerny-Turner spectrometer equipped with an intensified charge coupled device detector, which is operated in the fast kinetic mode. This diagnostic allows us to evaluate the temporal evolution of the electron density in the TESPEL ablation cloud. In order to gain information about the spatial distribution of the cloud parameters, a nine image optical system that can simultaneously acquire nine images of the TESPEL ablation cloud has recently been developed. Several images of the TESPEL ablation cloud in different spectral domains will give us the spatial distribution of the TESPEL cloud density and temperature.
