Electrocrushing drills and methods for operating electrocrushing drills. Electrocrushing
drill bits comprise one or more
high voltage electrodes surrounded by a ground or current return structure, which can be a ring or a comprise rod shaped electrodes. Openings in the rim of the current return structure facilitate removal of drilling debris and bubbles created by the electrocrushing process out from the bottom face of the bit and up the
wellbore. The
high voltage electrodes can be arranged in a circle. The current return structure may partially cover the bottom face of the
drill bit, thereby enclosing the
high voltage electrodes in openings that may be sector shaped. The
drill may comprise one or more conducting loops, in each of which pulsed current creates a pulsed
magnetic field. The loops can be oriented in particular directions to provide a pulsed
magnetic field with the desired configuration and orientation in space. The formation ahead of the drill can then be evaluated with the appropriate sensors.