For those who want to find out more about gyrotrons and drilling deep wells with them economically this guy from MIT started Quase Energy to exploit the technology mentioned in the article above. They use 28 GHz waves that pass right through the plasma generated while compressed air blasts it away and keeps the drill head cool, the borehole is glass lined by melted rock.
Paul Woskov - Into the Bedrock by Full Bore Millimeter-Waves
7,028 views Dec 28, 2015 [next] December 8–9, 2015 San Francisco, California
Into the Bedrock by Full Bore Millimeter-Waves
Drilling into deep crystalline basement rock is a bottleneck technology to accessing vast resources of geothermal energy and to a possible solution to the nuclear waste storage problem. Commercially available high power millimeter-wave sources developed for fusion energy research could be a drilling game changer by enabling full bore directed energy penetration. This wavelength range propagates well through optically obscure paths and is well absorbed by rock melt, it can be efficiently guided long distances, and sources come in megawatt average power size units that are over 50% efficient. The electricity costs to melt or vaporize through a hard rock formation could be less than 1/10 of current costs of a deep mechanical drilled hole in softer rock. Melt/vaporization experiments of granite and basalt with a 10 mm wave beam have established its feasibility in the laboratory at MIT.