3. Advanced design of the R-Tokamak

A medium-sized DT burning tokamak has been designed with low-activation Al-alloys. We can obtain a large plasma current up to 4.5 MA with an elongation of 2.3, by taking advantage of the good shell effect of Al-alloy vessel and by applying the appropriate feedback control system. Such a large current is effective for the improvement of confinement and high β-value.

To obtain these plasma parameters, PF coils are placed inside TFC. Single pancake windings and their connection by welding remove complexity originated from this configuration. By the use of keys in the extended wedge region and large shear panels the displacement of TFC caused by large overturning moment is suppressed to be less than 1 mm.

For reduction of induced activity, almost all the components have been designed with Al-alloys except TFC and inboard PFC conductors. The newly developed Al-alloy has been applied to the vacuum vessel, where the new structure of one-turn break is adopted using Al₂O₃ ceramic spraying. Gamma-rays from activated copper conductor in TFC and inboard PFC are shielded by a lead plate located between the vacuum vessel and PFC. This concept would be extended to devices which aim at Q ⪢ 1 and much longer burning time, if all the coils are made of Al-alloy of which contents of impurity and alloying element are well-controlled.