The ablation system (10) according to the invention works with an ablation probe (12, 12a) that comprises two alternatingly working spark plasma electrodes (31, 32). They generate a plasma beam (47, 48) having a non-circular cross-section, which beam is to be guided—transversely with respect to the large longitudinal axis of its preferably oval cross-section—over the tissue to be ablated, in particular the mucosa (14). In doing so, it is possible to treat large-area tissue regions by means of a reliable and easily controllable procedure.