Generation of terahertz radiation by an oscillating discharge, excited by short laser pulses, may be controlled by geometry of the irradiated target. In this work, an annular target with a thin slit is considered as an efficient emitter of secondary radiation when driven by a short intense laser pulse. Under irradiation, a slit works as a diode, which is quickly filled by dense plasmas, closing the circuit for a traveling discharge pulse. Such a diode defines the discharge pulse propagation direction in a closed contour, enabling its multiple passes along the coil. The obtained oscillating charge efficiently generates multi-period quasi-monochromatic terahertz waves with a maximum along the coil axis and controllable characteristics.