Magnetic islands play an important role in determining plasma transport in toroidal magnetic confinement systems. The magnetic error fields and the associated islands can be theoretically described by a Hamiltonian approach. Experiments have been conducted on the Compact Auburn Torsatron [Fusion Technol.18, 281 (1990)] to test the applicability and limits of the first‐order Hamiltonian theory to magnetic islands. A novel set of helical trim coils with the same spatial periodicity as an &igr;– = 1/2 magnetic island were used to create a perturbation field of variable magnitude and phase. Extensive experimental parametric studies of the magnetic island were conducted and compared with theory. It was found that the first‐order Hamiltonian theory is applicable for the complete range of experimental error fields.