Experiments of axial compression of flux-core-spheromak

The axial compression of flux-core spheromaks is successfully made in the TS-3 facility. Magnetic measurements show that oblate and singlet magnetic configurations are obtained by the axial compression. The closed poloidal magnetic flux surrounding the magnetic axis increases up to 6 mWb, that is three or four times larger than the closed poloidal magnetic flux obtained without the axial compression. During the early and middle phases of the compression, no global instabilities are observed, but, in the late phase, sudden collapses of the flux-core spheromak are observed. This may limit the maximum compression ratio. Fitting to an equilibrium model suggests that, by the axial compression, the ratio μ of the current density to the magnetic field, increases toward the value of the conventional spheromak without core flux. (author)