A pulsed power drilling system and method for breaking a mineral substrate by use of microwave radiation for ionizing a fluid volume

A method for breaking a mineral substrate by passing a pulsed electrical current through the mineral substrate by use of a pulsed power drilling system comprising a pulsed power generator and a drill head comprising a plurality of electrodes comprising a solid electrode portion configured to be connected to the pulsed power generator, the method comprising:

• positioning the drill head so that the plurality of solid electrode portions are at least in proximity of a surface of the mineral substrate;
• generating, by use of an arrangement for generating microwave radiation, microwave radiation used for at least partly and temporarily ionizing a fluid volume extending from a solid electrode portion of a first electrode to a surface of the mineral substrate;
• emitting the generated microwave radiation in the fluid volume;
• generating, by use of a pulsed power generator, a high voltage current pulse;
• and
• passing the high voltage current pulse between said electrode portion of a first electrode and a solid electrode portion of a second electrode of the drill head via the at least partly ionized fluid volume and the mineral substrate.