Twenty barrel in situ pipe gun type solid hydrogen pellet injector for the Large Helical Device.
A 20 barrel solid hydrogen pellet injector, which is able to inject 20 cylindrical pellets with a diameter and length of between 3.0 and 3.8 mm at the velocity of 1200 m/s, has been developed for the purpose of direct core fueling in LHD (Large Helical Device). The in situ pipe gun concept with the use of compact cryo-coolers enables stable operation as a fundamental facility in plasma experiments. The combination of the two types of pellet injection timing control modes, i.e., pre-programing mode and real-time control mode, allows the build-up and sustainment of high density plasma around the density limit. The pellet injector has demonstrated stable operation characteristics during the past three years of LHD experiments.
Performance of fueling pellet injectors for the large helical device
Abstract Techniques of solid hydrogen pellet injection into plasmas towards steady state operation as well as further reliable hardware have been demonstrated for the large helical device (LHD). The conversion of hardware is performed to attain higher reliability and reproducibility of pellets. Major issues to improve the quality of pellets are the cooling temperature of pellet production by a cryo-cooler and the incident angle to the inner wall of the guide tube for pellets. The former is improved from 12.6 to 10.6 K by the reduction of the heat conduction and radiation to produce the robust pellets. The latter is optimized from 5.41° to 1.73° at the maximum by the low-angle pellet path to mitigate the destruction of pellets in the guide tube. It has been confirmed by these conversion that the quality of pellets is significantly improved, i.e., the probability of intact pellets is increased to ∼100%. Also, the controllability of the pellet size is desired as needs of pellet injection experiments. It has been demonstrated by the property of pellet production related to the cooling temperature and the pressure of supplied hydrogen gas.
Mass Loss History of Evolved Stars
We provide high-resolution maps of the circumstellar dust shells of several dozen Asymptotic Giant Branch (AGB) stars using data from the Spitzer space telescope Multiband Imaging Photometer (MIPS) imaged at 70μm. AGB stars are the major contributors of chemical elements such as carbon, oxygen and silicon, which are essential to the existence of life in the universe, through mass loss processes that take place at the surface of the star. We probe the spatial distribution of cold (∼40 K) dust grains in order to trace the history of mass loss from the observed radial density variation in these shells. Our images illustrate that different morphologies may evolve because AGB stars can already interact with the interstellar medium (ISM) that surrounds them even at these early stages of the AGB mass loss history. Relative motion of the star as well as the ISM with respect to the local environment may be of particular importance for shell structure evolution.