A 650 MWe D-T fusion reactor “KARIN-I” possesses 10 moving ring plasmas which are produced by relativistic electron beam (REB) injection, heated by a major radius compression and transported in a linear cylindrical burning chamber by annularly flowing liquid lithium outside the SiC first wall. The liquid lithium not only stabilizes the tilting motion of the ring plasmas but also works as a tritium breeder and main coolant. Energy of burnt plasmas is efficiently recovered by the major radius expansion. The linear alignment of reactor components ensures easy assembly and disassembly, and also provides simple maintainability of the system.