Millimetre Wave Drilling

Millimetre wave ("MMW") drilling is an advanced directed-energy drilling technology that uses high-power electromagnetic radiation in the 30–300 GHz frequency range, generated by a gyrotron, to melt, spall, and vaporize rock without mechanical contact. The technology was invented by Paul Woskov at MIT's Plasma Science and Fusion Center beginning in 2008, building on decades of gyrotron development for nuclear fusion plasma heating. Unlike conventional rotary drilling — where mechanical bits grind through rock and degrade rapidly in hard, hot formations — MMW drilling transmits concentrated energy downhole through a metallic waveguide to ablate rock at the borehole face, producing fine volcanic-like ash that is flushed to the surface by circulating gas. The technology is specifically designed to overcome the depth and temperature limitations of mechanical drilling in crystalline basement rock (granite, basalt), potentially enabling boreholes to 15–20 km depth where temperatures exceed 400°C — accessing the superhot rock ("SHR") geothermal resource that could provide terawatt-scale clean baseload power. Quaise Energy, the MIT spinout commercializing the technology, achieved a record 100-meter MMW drilling depth in granite at a Central Texas field site in July 2025, drilling at speeds up to 5 m/hr (vs. ~0.1 m/hr conventional average in granite). The company has raised over $95 million from investors including Mitsubishi, plans to deploy a 1 MW commercial-scale gyrotron system, and targets a pilot superhot geothermal power plant in the Western U.S. by 2028. However, the technology remains at an early demonstration stage — the 100-meter field record is a small fraction of the 10–20 km commercial target depths, and critical challenges around borehole stability, waveguide durability at extreme depths, and debris management at scale are not yet resolved.

The concept of using directed energy beams to penetrate rock has been explored periodically since the mid-20th century, but millimetre wave drilling as a practical technology traces directly to the work of Paul Woskov at MIT's Plasma Science and Fusion Center ("PSFC").

Foundational Research at MIT (2008–2018)

In 2008, Woskov — a senior research engineer with decades of experience using gyrotrons to heat plasma for fusion energy research — recognized that the same high-power millimetre-wave technology could be applied to vaporize rock. He and PSFC colleague Dan Cohn received a seed grant from the MIT Energy Initiative ("MITEI") in late 2008 to investigate the concept. Using a 10 kW gyrotron operating at 28 GHz, Woskov conducted a series of experiments at the PSFC, blasting blocks of granite, basalt, and limestone with high-intensity millimetre-wave beams. The experiments demonstrated that MMW energy could melt, spall, and vaporize hard crystalline rock, producing clean holes with vitrified (glassified) walls. Woskov calculated that a megawatt-class gyrotron directed through a 20 cm waveguide could blast a basketball-sized hole into rock at a rate of 20 m/hr — which, if sustained, would create the world's deepest borehole in about 25.5 days of continuous drilling. The research was supported by MITEI and subsequently by the U.S. DOE. In 2014, Impact Technologies published a Final Technical Report for DOE/ARPA-E documenting the capabilities of high-energy beams for drilling through very hard, very hot rocks for geothermal, nuclear waste storage, and oil and gas applications.

AltaRock and ARPA-E (2018–2022)

In parallel, AltaRock Energy, a Seattle-based enhanced geothermal company, led an ARPA-E-funded initiative (US $3.9 million, three-year grant) to demonstrate MMW drilling at increasingly larger scales, from hand-sized rock samples to room-sized slabs. The project used megawatt-class gyrotrons at Oak Ridge National Laboratory ("ORNL") and included partners from MIT, Impact Technologies, and ORNL. This work produced key experimental results on confined and unconfined melt drilling in basalt and granite at elevated pressures simulating downhole conditions.

Quaise Energy and Commercialization (2018–Present)

In 2018, Carlos Araque (former technical director of MIT's The Engine accelerator) and Matt Houde co-founded Quaise Energy to commercialize Woskov's MMW drilling technology for superhot geothermal energy. Quaise has raised over $95 million from investors including Mitsubishi Corporation, Prelude Ventures, Safar Partners, and Standard Investments. The company's progression from laboratory to field has been rapid. Testing began at ORNL in October 2021 with initial gyrotron boring experiments. Quaise established a development campus in Houston, Texas, reaching its internal "100x" drilling target by 2023 and testing at higher power throughout 2024. In January 2025, Quaise demonstrated MMW drilling outside a laboratory for the first time in history, firing millimetre waves into the ground from its Houston facility. In May–June 2025, the company conducted tests at a Nabors Industries drilling rig, drilling 4-inch diameter holes to depths of 30–40 feet through columns of basalt. In July 2025, Quaise achieved a record 100-meter (118-meter in a subsequent test) MMW drilling depth in a granite quarry near Austin, Texas, operating at speeds 10 times faster than prior demonstrations and up to 5 m/hr — approximately 50 times faster than the conventional average drilling rate in granite (~0.1 m/hr). Live public demonstrations were held biweekly from September through November 2025. Quaise is simultaneously developing its first superhot geothermal power plant in Oregon, initially using conventional drilling to demonstrate geothermal power production from 350°C rock, with plans to deepen the wells using MMW drilling in the future. The company targets an operational pilot plant by 2028 and has articulated an ultimate vision of converting existing coal and gas-fired power plants to geothermal steam by drilling superhot wells on existing plant sites.

Energy Source: The Gyrotron

MMW drilling is powered by a gyrotron — a type of high-power vacuum electron device (also known as an electron cyclotron maser) that generates coherent electromagnetic radiation in the millimetre-wave frequency range (30–300 GHz, corresponding to wavelengths of 1–10 mm). Gyrotrons were developed in the Soviet Union in 1964 and have been refined over six decades primarily for nuclear fusion research, where they are used to heat plasma to extreme temperatures (over 100 million °C) in tokamaks and stellarators. Gyrotrons are the most powerful source of coherent electromagnetic radiation in the millimetre-wave band, capable of generating megawatt-scale continuous-wave ("CW") power at energy conversion efficiencies of approximately 50% — far superior to lasers, which typically achieve approximately 10% efficiency and cannot sustain comparable power levels in continuous mode. Commercially available 1 MW CW gyrotron systems are rugged enough for industrial use and have been demonstrated to operate continuously for hours.

The gyrotron sits at the surface. It does not go downhole. This is a critical design advantage: the only components exposed to the extreme downhole environment are the passive metallic waveguide and the purge gas, with no electronics, motors, seals, or moving parts at the borehole face.

Energy Transmission: The Waveguide

The millimetre-wave beam generated by the surface gyrotron is transmitted to the bottom of the borehole through a corrugated metallic waveguide — a precision-engineered hollow metal tube that guides the electromagnetic energy with minimal loss over long distances. The waveguide is positioned near-vertically in the borehole, with gravity assisting alignment. The corrugated interior surface is designed to propagate the low-loss HE₁₁ waveguide mode. At the bottom of the waveguide, the concentrated beam exits and strikes the rock surface.

The waveguide also serves as the conduit for the purge gas system: gas (air or nitrogen) is injected down the waveguide alongside or around the beam, and debris-laden gas returns to the surface through the annular space between the waveguide exterior and the borehole wall.

Rock Destruction Mechanism

When the high-power MMW beam reaches the rock surface at the bottom of the borehole, it deposits energy through dielectric heating — the same fundamental mechanism that heats food in a microwave oven, but at vastly higher power densities. The interaction between the millimetre waves and the rock progresses through three regimes depending on the power density:

Thermal Spallation: At lower power densities, the rapid, localized heating creates thermal stress gradients that cause the rock surface to fracture and spall — small fragments crack off the rock face. This is the dominant mechanism in the early stages and for some rock types.

Melting: At higher power densities, the rock surface temperature exceeds the melting point of the mineral constituents (typically 1,000–1,500°C for common silicate rocks), and the rock liquefies. The molten material is displaced by gas pressure and beam momentum.

Vaporization: At the highest power densities, the rock is heated past its vaporization temperature, converting solid rock directly into a plume of nanoparticle-sized vapor/ash. The vapors cool rapidly in the purge gas stream and solidify into extremely fine particles (volcanic-like ash).

In practice, all three mechanisms operate simultaneously at different radial positions on the borehole face. The combination of spallation, melting, and vaporization creates a borehole with a smooth, vitrified (glassified) wall where the molten rock has resolidified into a glassy lining.

Debris Removal

The fine ash and nanoparticle debris produced by MMW drilling are removed from the borehole by a circulating purge gas (typically compressed air or nitrogen). The gas is injected downhole through or alongside the waveguide, sweeps across the rock face to carry debris away, and returns to the surface through the annular space between the waveguide and the borehole wall. At the surface, the debris-laden gas passes through collection systems. Conventional particle filters cannot capture nanoparticle-sized debris, so the exhaust is typically bubbled through a water collection pond to trap the solids. The fine particle size of the debris — far smaller than the cuttings produced by mechanical drilling — is actually an advantage for removal from extreme depths, because smaller particles are easier to suspend and transport in a gas stream over long vertical distances.

Borehole Geometry and Self-Casing

The MMW drilling process produces a circular, smooth-walled borehole. The intense heat at the borehole wall melts a thin layer of rock, which resolidifies as a glassy (vitrified) lining upon cooling. This vitrification may serve a dual purpose: stabilizing the borehole wall against collapse and reducing permeability to prevent fluid infiltration — potentially eliminating or reducing the need for conventional steel casing. If validated at depth, this self-casing effect would eliminate one of the most expensive and time-consuming aspects of conventional deep well construction.

Hybrid Drilling Architecture

Quaise Energy's commercial concept uses a hybrid architecture: conventional rotary drilling through the upper sedimentary rock layers (where it is fast and cost-effective), followed by a transition to MMW drilling in the hard crystalline basement rock layer (typically beginning at 2–5 km depth depending on geology). The conventional drilling rig sets steel casing through the sedimentary section, then the MMW system is deployed into the cased borehole to continue drilling through basement rock to target depths of 10–20 km. This approach leverages the existing oil and gas drilling industry's infrastructure and expertise for the upper portion while deploying MMW technology only where it provides a decisive advantage.

Target Application: Superhot Rock Geothermal

The intended application of MMW drilling is to access superhot rock ("SHR") geothermal resources at depths where temperatures exceed 374°C (the supercritical point of water) and preferably above 400°C. At these temperatures, geothermal fluids become supercritical, dramatically increasing their energy content and the power output per well. A single SHR geothermal well could produce 5–10 times more power than a conventional geothermal well, meaning far fewer wells are needed for a given plant capacity. AltaRock's techno-economic analyses project that SHR resources enabled by MMW drilling could achieve an LCOE below $50/MWh, making deep geothermal cost-competitive with fossil fuels. Quaise's longer-term vision involves repowering existing coal and natural gas power plants by drilling SHR wells on existing plant sites and converting the plants to run on geothermal steam, reusing the existing turbines, generators, grid connections, and workforce.

MMW drilling represents a fundamentally different approach to the deep drilling problem compared to the incumbent technology: conventional rotary drilling with mechanical bits.

No Mechanical Bit Wear

Conventional drilling uses rotating drill bits — typically polycrystalline diamond compact ("PDC") or roller cone bits — that physically grind through rock. In hard crystalline basement rock (granite, basalt, gabbro), these bits wear down rapidly, requiring frequent and costly round-trips to the surface for replacement. Each round-trip ("tripping") becomes progressively more time-consuming and expensive as the borehole deepens, because the entire drill string must be pulled out and reinserted. This is a primary reason why conventional drilling costs escalate exponentially with depth beyond about 5–7 km. MMW drilling has no downhole mechanical components that contact rock — the energy beam does the work. There is no bit to wear out, no need for drilling mud to lubricate and cool the bit, and no mechanical tripping required for bit replacement. This eliminates a fundamental cost driver that makes ultra-deep conventional drilling uneconomic.

Linear vs. Exponential Cost Scaling

Perhaps the most commercially significant difference is the cost profile with depth. Conventional drilling costs increase exponentially with depth due to cumulative bit wear, tripping time, and increasing difficulty of circulating drilling fluids at extreme depths and temperatures. A 2021 GRC Transactions techno-economic analysis found that MMW drilling costs are projected to scale linearly with depth at approximately $1,000/m, because the rate of penetration remains constant regardless of depth (the beam energy does not diminish with distance, and there are no downhole components that degrade). At these projected rates, deep geothermal wells at 10–20 km would cost $10–20 million — a fraction of what conventional or even advanced mechanical drilling would cost to reach comparable depths.

Access to Superhot Rock Resources

Conventional drilling technology is limited to depths where rock temperatures remain below approximately 200–300°C. Above these temperatures, drilling muds break down, elastomeric seals fail, and electronic downhole tools stop functioning. MMW drilling has no downhole electronics, no drilling mud, and no elastomeric components — the only thing going downhole is the waveguide and purge gas. This makes MMW drilling uniquely suited to the extreme conditions of superhot rock (400°C+) at depths of 10–20 km, where the geothermal resource is 10x more powerful than conventional geothermal and accessible virtually everywhere on Earth.

Borehole Self-Sealing

When MMW energy melts and vaporizes rock, the intense heat vitrifies (glassifies) the borehole wall, creating a smooth, glassy lining. This vitrified layer may serve as a natural casing, reducing or eliminating the need for steel well casing — a major cost component of conventional deep wells. However, the structural integrity of vitrified boreholes under extreme pressure at multi-kilometer depths remains unproven.

Hybrid Drilling Approach

Quaise Energy's commercial strategy acknowledges that MMW drilling is not superior to conventional methods in all conditions. In softer sedimentary rock near the surface, conventional rotary drilling is faster, cheaper, and well-optimized. Quaise proposes a hybrid approach: conventional drilling through the sedimentary layer, followed by MMW drilling through the hard crystalline basement rock where mechanical bits struggle. This leverages the strengths of both technologies.

MMW drilling faces substantial challenges in scaling from laboratory and early field demonstrations to commercial deep geothermal drilling.

Technology Readiness

As of early 2026, the maximum depth achieved by MMW drilling is approximately 100–118 meters, drilled in granite at Quaise Energy's Central Texas quarry site. The commercial target is 10–20 km — roughly 100–200 times the current demonstrated depth. The technology has progressed rapidly (from centimeter-scale lab experiments before 2024 to 100 meters in 2025), but the gap between current capability and commercial requirements remains enormous. Each order-of-magnitude increase in depth introduces new engineering challenges related to waveguide integrity, beam alignment, debris management, borehole stability, and thermal management.

Waveguide Durability and Beam Transmission

The corrugated metallic waveguide that transmits the MMW beam from the surface gyrotron to the borehole face must maintain precise alignment and structural integrity over distances of 10–20 km under extreme downhole conditions: temperatures exceeding 400°C, pressures of hundreds of MPa, and mechanical stresses from the weight of the waveguide itself. Maintaining efficient beam transmission over these distances without excessive power loss, mode conversion, or waveguide deformation is an unsolved engineering challenge. MIT PSFC has proposed the world's first dedicated MMW drilling laboratory specifically to test durable waveguides and high-power RF transmission under simulated deep conditions.

Borehole Stability and Casing

While MMW drilling vitrifies the borehole wall, it is not yet known whether this glassy lining can maintain structural stability at depths of 10+ km under the extreme pressures and temperatures of the deep subsurface. Conventional deep wells require steel casing cemented into the borehole at multiple intervals to prevent collapse and seal off water-bearing formations. If vitrification alone is insufficient, some form of casing or lining will be needed — which would reintroduce many of the cost and complexity challenges that MMW drilling is designed to eliminate.

Debris Management at Scale

MMW drilling produces fine volcanic-like ash (nanoparticle-sized debris) from vaporized rock. This debris is flushed to the surface by a circulating purge gas (air or nitrogen). At laboratory scale, debris management is straightforward, but at commercial depths of 10–20 km, maintaining effective gas circulation and debris removal through a narrow waveguide annulus presents significant challenges. Conventional drilling muds, which serve this purpose in rotary drilling, are incompatible with MMW systems because they would absorb the millimetre-wave energy. The purge gas must also manage downhole pressure to prevent borehole collapse.

Power Requirements and Gyrotron Scale-Up

Current Quaise field tests use a 100 kW gyrotron system. Commercial-scale operations require gyrotrons of 1 MW or more, operating continuously for extended periods (potentially weeks or months for a single deep borehole). While 1 MW continuous-wave gyrotron systems exist commercially (developed for fusion energy research), adapting them for the rugged field conditions of a drilling site — with the associated vibration, dust, and logistical challenges — requires significant engineering. Gyrotrons also require superconducting or high-field magnets for their operation, adding cost and complexity.

Lack of Operating Experience

No MMW drill has ever produced a geothermal well. The technology has zero hours of commercial drilling operation. The entire evidence base consists of laboratory experiments at MIT and Oak Ridge National Laboratory and early field demonstrations at Quaise's Texas quarry site. Critical questions — including long-term borehole stability, achievable commercial rates of penetration at depth, waveguide lifetime, and cost per meter at scale — can only be answered through substantially deeper drilling campaigns and, ultimately, by completing and operating a geothermal well.

Regulatory and Permitting Uncertainty

MMW drilling is a novel technology that does not fit neatly into existing drilling regulatory frameworks. Regulators have no experience permitting directed-energy drilling systems, and questions about safety (high-power electromagnetic radiation near workers), environmental impact (nanoparticle emissions, gas venting), and well integrity assurance will need to be addressed before commercial deployment. Quaise's planned pilot plant in Oregon will provide the first regulatory test case.