Recent progress of studies on plasma-detachment and plasma-material interactions by utilizing linear plasma devices developed in Nagoya University

   The recent progress of plasma-detachment research as well as plasma-material interaction studies in Nagoya Univ. are outlined in this seminar. Research on plasma detachment, which is thought to be one of the most promising methods to reduce heat load on divertor plate, is currently underway in the linear diverter plasma simulator, NAGDIS-II. We have measured the detailed plasma structure around the recombination front region by using 2D Langmuir probe system and Thomson scattering diagnostics. Plasma instabilities observed near the recombination front strongly enhances cross-field plasma transport. The local enhancement of the cross-field plasma transport makes inverse plasma flow along the magnetic field at the peripheral region of plasma column. We have also investigated the effects of magnetic field structure on detached plasma formation by simulating magnetically expanding and contracting plasma. Under the detached plasma condition, the magnetically expanding plasma clearly exhibited a significant degradation of detached plasma formation. Further, a compact divertor plasma simulator (CDPS) has been developed for plasma-wall interaction study on neutron-irradiated materials toward ITER and DEMO. ITER-like W specimens irradiated by neutrons to 0.06 dpa in a fission reactor, were exposed to a deuterium plasma in the CPDS. The experimental results clearly show the broadening of TDS spectrum toward high temperature region leading to a significant increase in the total deuterium retention in the neutron-irradiated W. The total deuterium retention is found to be proportional to the square root of the plasma exposure time.