Spontaneous formation of toroidal flow was measured for the first time in oblate FRCs produced in TS-3 and 4 experiments. The toroidal ion flow (V i ≈10km/sec) was found to peak around the magnetic axis, indicating formation of high flow shear inside the separatrix. The toroidal flow was observed to deform the magnetic field lines of the FRC, producing bipolar toroidal field profile. In highs FRC (averaged number of ion gyro-radius "s"=4.5) with slow flow, its n=1 mode kept growing, causing collapse of the whole configuration. However, in lows FRC (s=3) with fast flow, the rotating n=2 mode (saturated) became dominant after n=1 mode saturation. The spontaneous formation of flow shear possibly transformed the n=1 mode into the n=2 mode, suggesting a new sheared flow stabilization of n=1 mode. The flow shear was also generated artificially using the "sling shot" effect of the counterhelicity reconnection. The n=1 and 2 mode amplitudes were reduced down to 1/5-1/10 due to the generated flow shear. A new method for continuous sheared-flow generation was proposed for stabilization and heating of FRC by use of intermittent merging of spheromaks with opposing B t .

Ion kinetic effect on the bifurcated relaxation of merging spheromaks to a field-reversed configuration (FRC) was studied experimentally using varied € S * which is the ratio of the minor radius to the ion skin depth from 1 to 7. The two merging spheromaks were observed to relax to an FRC or a new spheromak depending on whether the initial poloidal eigen value was smaller or larger than a threshold value. The threshold initial poloidal eigen value for the relaxation to an FRC increased with decreasing € S * value. Decrease in € S * promoted the relaxation to an FRC, annihilating the magnetic helicity, in sharp contrast with the conventional Taylor relaxation. Suppression of the low-n mode by the rotation shear of the toroidal modes is the most probable reason why the low-€ S * condition promotes the relaxation into an FRC. € S * is important factor to measure both ion kinetic effect and two-fluid effect. Ions become unmagnetized and the motion of ions decouples with those of electrons under the small € S * regime, promoting ion kinetic effect and two-fluid effect [6]. Interest has grown in experimentally studying the relaxation to an FRC under varied € S * condition. This non-M HD stability effect closely relates with a high-beta/ high-flow equilibria useful for the future large-scale FRC and the high-beta ST experiments. This paper studies experimentally this bifurcated relaxation of two merging spheromaks in a wide range of € S * numbers. Several ion species were used in the up-scaled TS-4 device in order to vary € S * widely from 1 to 7.

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