Free electron laser Terahertz source（FEL-THz） has significant advantages, such as wide and continuously adjustable spectrums. A compact terahertz source is desired to reduce the cost and space but still provide high-quality terahertz beams. However, the space constraints requires all the magnets should be downscaled as well. In this paper, a combined-function corrector is designed, capable of providing vertical and horizontal correction at the same time. Poisson and Opera-3D have been used to design and optimize the magnet. The vertical correction is mainly performed by shimming and trimming the magnetic pole head, and the horizontal correction is mainly performed by adjusting the current coil. As a result, the good field range of the vertical field and the horizontal field reach the expected value, and the relative error of the integrated field meets the requirements of beam correction.

THz source; corrector magnet; dipole magnet; field homogeneity; end chamfer