End effects on the n = 2 rotational instability in the reversed-field theta-pinch

End effects of the field-reversed configuration created by a θ-pinch were studied with long solenoidal guide field (GF) attached at both ends of the main θ-pinch coil. It was observed that the onset time of the n = 2 rotational mode (n is the azimuthal mode number) could be delayed with the GF until the endshorting effects propagated back to the main coil. Measurements of the plasma rotation just outside the separatrix showed that the n = 2 mode began to develop when the external plasma was spun up to a certain level in the direction of the ion diamagnetic current. These observations suggest that the n = 2 mode is driven by the endshorting effects.