Measurements of the Characteristics of Fine Grain Graphite Used as a First Wall Material for the T-15MD TOKAMAK

Abstract

In this work, properties of fine grain graphite that will be used as a plasma-facing material in the T-15MD Tokamak are measured and studied. Density and porosity, thermal diffusivity and thermal conductivity, as well as the crystal grain size and impurity content of graphite are measured. The measurement results were compared to the corresponding parameters of MPG-6, MPG-7 and MPG-8 graphites. Characteristics of hydrogen and methane retention in graphite and conditions of their desorption depending on temperature of preliminary annealing, its duration, exposition of fully annealed samples in atmospheric gas at normal conditions. Influence of irradiation of the samples by deuterium ions with different energies on the characteristics of hydrogen trapping and desorption. In all cases, attention was paid to the possibility of influence of experimental conditions on trapping and desorption of hydrogen left in graphite after its production, as well as the one trapped from the atmosphere. Based on the data obtained and the expected conditions in the T-15MD’s plasma chamber, optimal modes for annealing of graphite received from producer and temperatures of the tokamak’s plasma-facing elements that assist in removal of hydrogen from graphite are determined.