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In nuclear fusion power research, the plasma-facing material (or materials) (PFM) is any material used to construct the plasma-facing components (PFC), those components exposed to the plasma within which nuclear fusion occurs, and particularly the material used for the lining or first wall of the reactor vessel. Fusion reactor designs must consider three overall steps for energy generation: # Generating heat through fusion, # Capturing heat in the first wall, # Transferring heat at a faster rate than capturing heat. Currently, fusion reactor research focuses on improving efficiency and reliability in heat generation, capture, and rate of transfer. Generating electricity from heat is beyond the scope of current research due to existing efficient heat-transfer cycles, such as heating water to operate steam turbines that drive electrical generators. Current fusion reactors are fueled by deuterium-tritium (D-T) fusion reactions, which produce high-energy neutrons that can damage the first wall.〔 1 November 2015 ''Lithium As Plasma Facing Component for Magnetic Fusion Research.''〕 Tritium is not a commonly available isotope due to its short half-life but can be bred by the nuclear reaction of lithium (Li) isotopes with high-energy neutrons that collide with the first wall.〔Molokov, S. S.; Moreau, R.; Moffatt K. H. ''Magnetohydrodynamics: Historical Evolution and Trends,'' p. 172-173.〕 ==Requirements== Most magnetic confinement fusion devices (MCFD) consist of several key components in their technical designs, including: * Magnet system: confines the deuterium-tritium fuel in the form of plasma and in the shape of a torus. * Vacuum vessel: contains the core fusion plasma and maintains fusion conditions. * First wall: positioned between the plasma and magnets in order to protect outer vessel components from radiation damage. * Cooling system: removes heat from the confinement and transfers heat from the first wall. The core fusion plasma must not actually touch the first wall. ITER and many other current and projected fusion experiments, particularly those of the tokamak and stellarator designs, use intense magnetic fields in an attempt to achieve this, although plasma instability problems remain. Even with stable plasma confinement, however, the first wall material would be exposed to a neutron flux higher than in any current nuclear power reactor, which leads to two key problems in selecting the material: * It must withstand this neutron flux for a sufficient period of time to be economically viable. * It must not become sufficiently radioactive so as to produce unacceptable amounts of nuclear waste when lining replacement or plant decommissioning eventually occurs. The lining material must also: * Allow the passage of a large heat flux. * Be compatible with intense and fluctuating magnetic fields. * Minimize contamination of the plasma. * Be produced and replaced at a reasonable cost. Some critical plasma-facing components, such as and in particular the divertor, are typically protected by a different material than that used for the major area of the first wall.〔http://www.apam.columbia.edu/courses/apph4990y_ITER/Divertor%20Presentation%20-%20Stoafer.pdf retrieved 11 September 2012〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Plasma-facing material」の詳細全文を読む スポンサード リンク
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