Part 1 of 2 Parts
    Paul Woskov is a senior research engineer at MIT’s Plasma Science and Fusion Center (PSFC). He is using a gyrotron, a specialized radio-frequency (RF) wave generator developed for fusion research, to explore how millimeter RF waves can open holes through hard rock by melting or vaporizing it. Drilling deep into hard rock is necessary to access huge geothermal energy resources, to mine precious metals, or explore new options for nuclear waste storage. However, it is a difficult and expensive process. Today’s mechanical drilling technology has serious limitations. Woskov believes that powerful millimeter microwave sources could increase deep hard rock penetration rates by over ten times at a lower cost over current mechanical drilling systems, while providing other practical benefits.
     Woskov says, “There is plenty of heat beneath our feet, something like 20 billion times the energy that the world uses in one year.” However, Woskov notes, most studies of the accessibility of geothermal energy are based on current mechanical drilling technology and its limitations. They do not consider the idea that a breakthrough in drilling technology could make possible deeper, less expensive penetration, opening into what Woskov calls “an enormous reserve of energy, second only to fusion: base energy, available 24/7.”
     Current rotary drilling technology is a mechanical grinding process that is limited by rock hardness, deep pressures, and high temperatures. Specially designed “drilling mud,” pumped through the hollow drill pipe interior, is used to enable deep drilling. It allows the removal of the excess cuttings, returning them to the surface via a ring-shaped space between the drill pipe and borehole wall. The pressure of the mud also keeps the sides of the hole from collapsing. It seals and strengthens the hole in the process. But there is a limit to the pressures such a borehole can withstand.  Typically, boreholes cannot be drilled to a depth beyond 30,000 feet.
      Woskov asks, “What if you could drill beyond this limit? What if you could drill over thirty-three thousand feet into the Earth’s crust?” With his proposed gyrotron technology this depth is theoretically possible.
     Woskov reveals that drilling engineers have a hard time believing his method does not use the costly drilling mud they depend on. But, he explains, with a gyrotron, high-temperature physics takes the place of the mechanical functions of low-temperature mud. It will allow drillers to extract rock matter through vaporization or displace the melt through pressurization. Similarly, the high temperature melted rock will seal the walls of the borehole. The high pressure from the increased temperature will prevent borehole collapse. An increase in temperature in a confined volume will always result in an increase in pressure over local pressure. This means that drillers could maintain the stability of a borehole to greater depths than possible with drilling muds.
     Woskov mentions yet another advantage: “Our beams don’t need to be round. Forces underground are anisotropic — not symmetrical. That is one reason holes collapse. But we can shape our beam to respond to local pressures. You can create an elliptical hole with the major axis corresponding to the anisotropy of the forces, essentially recovering the strength of a round hole in a symmetrical force field.”
     Later this spring, Woskov is planning to move his base of operation from the PSFC to the Air Force Research Lab (AFRL) in Kirkland, New Mexico. This move will take advantage of a microwave source that will allow him to perform experiments at a power level a factor of ten higher than is currently possible in the laboratory at MIT. He would be able to graduate from drilling rocks in the four-to-six-inch range to those in the two-to-four-foot range. He is especially interested in exploring how well the rock can be vaporized. This would only be possible with the higher power available at AFRL.
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