By concept development of the compact volumetric neutron source on the spherical tokamak JUST basis for minor actinides transmutation with aspect ratio A ¼ 2, some key plasma physics problems are arising: start of discharge; plasma current maintenance in stationary stage; appropriate neutron fluence for transmutation. On the basis of accepted physical and technical preconditions of the concept the combined scenario of current start and ramp-up, its stationary maintenance due to bootstrap effect and drive by neutral particle injection are considered. The plasma current is proposed to be initiated inductively and then bootstrap current will generate with using additional heating by injection of neutral beams. Necessary neutron flux for effective transmutation (G n % 0.4 MW=m 2 ) will be reached by both plasma-beam reactions and thermal plasma fusion reactions. By the way of preliminary consideration engineering studies of vacuum chamber, toroidal magnetic system, divertor, and blanket with energy multiplication ME % 20-100 are presented.

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