1990 Volume 110 Issue 12 Pages 1013-1019
New RF coils of L-C-R connection loops type are proposed. One of the coils is only a bundle of μ order diameter isolated conductor, facing the both sides of the bundle ends each other for a capacity. The next characters were found by experiments. (1) This type coils show a sharp first resonance mode and few other modes are measured. (2) The complete proportional relation between the number of the conductors and the conductance of the bundle. (3) The ratio of the RF current resistance to the direct current resistance can be 1.
Variational principle for eigenvalue problem was considered for it. The loss due to the vortex current in the conductor itself when exposed in the magnetic field was calculated accurately. And it was found that when the diameter of the conductor is 1/3 of the high frequency skin depth δ, the vortex current is very small. The litz wire can be used below 10 kHz. But this coil can be used above 100MHz (δ_??_7μ), because this coil need not to be stranded.
For example, the turbulent heating at the axis of a tokamak plasma in μs order is possible, when a large amplitude stationary magnetosonic wave is excited by the magnetic piston of these coils array around the plasma. And the distance between the plasma and the coils can be large. The commercial nuclear fusion is thought to be possible.