  Generation of terahertz radiation by an oscillating discharge, excited with
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 the irradiation, a slit works as a diode, which is quickly filled by
dense plasma, closing the circuit for a travelling 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 terahertz waves with a maximum along the coil axis and
controllable characteristics.
