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 clo sed poloidal magnetic flux surrounding the magnetic axis increases up to 6 m Wb, that is three or four times larger than the closed poloidal magnetic flux obtained without the axial compression. During the earl y and middle phases of the compression, no global instabilities are ob served, but, in the late phase, sudden collapses of the flux-core sphe romak are observed. This may limit the maximum compression ratio. Fitt ing to an equilibrium model suggests that, by the axial compression, t he ratio mu of the current density to the magnetic field, increases to ward the value of the conventional spheromak without core flux.