[en] The presence of large magnetic islands associated with rational magnetic surfaces in toroidal fusion devices can lead to a reduction of the confinement time of plasmas in such devices. In stellarators and torsatrons, the island size is usually minimized by careful design and coil construction within close tolerances in order to reduce the effect of error fields. In addition, magnetic islands resulting from unavoidable error fields can be reduced or eliminated through the use of auxiliary trim coils. The Compact Auburn Torsatron has been equipped with two pairs of large Helmholtz coils producing mutually orthogonal magnetic fields in the horizontal plane. These trim coils are used to control the size and phase of the t=1/2 magnetic island. A reduction of the inherent t=1/2 magnetic island size by a factor of three is achieved through a systematic variation of both horizontal trim field components. The minimization of the island size occurs simultaneously with the largest poloidal rotation rate of the island as a function of the correction coil current. (author). 8 refs, 7 figs