A probe for measuring electrical characteristics of an excitation current of a plasma is provided. The probe is mounted on a conductive line that includes an inner conductor and an outer conductor. The probe includes a current sensor and a voltage sensor. The current sensor includes a groove formed in the ground of one of the conductors in order to form a detour for the current flowing through the conductor, and a point for measuring electric voltage between a ground connected to the conductor and a point of the groove. The current sensor thus is able to measure a voltage proportional to the first time derivative of intensity (I.sub.plasma) of the excitation current. The voltage sensor is a shunt sensor capable of measuring a voltage proportional to the first time derivative of the voltage (V.sub.plasma) of the excitation current. A plasma reactor including a probe of the aforementioned type is also provided.