(FT/P1-13) A Tokamak with Nearly Uniform Coil Stress Based on Virial Theorem

**Abstract.** A novel tokamak concept with a new type of toroidal field (TF)
coils and a central solenoid (CS) whose stress is much reduced to a
theoretical limit determined by the virial theorem has been
devised. Recently, we had developed a tokamak with force-balanced coils
(FBCs) which are multi-pole helical hybrid coils combining TF coils and a CS
coil. The combination reduces the net electromagnetic force in the direction
of major radius. In this work, we have extended the FBC concept using the
virial theorem. High-field coils should accordingly have same averaged
principal stresses in all directions, whereas conventional FBC reduces
stress in the toroidal direction only. Using a shell model, we have obtained
the poloidal rotation number of helical coils which satisfy the uniform
stress condition, and named the coil as virial-limited coil (VLC). VLC with
circular cross section of aspect ratio A=2 reduces maximum stress to 60%
compared with that of TF coils. In order to prove the advantage of VLC
concept, we have designed a small VLC tokamak Todoroki-II. The plasma
discharge in Todoroki-II will be presented.

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*IAEA 2003*