Serious efforts to harness fusion energy began in the 1950s in government funded national labs and universities. Historically very few companies pursued fusion energy because of prohibitively high development costs and uncertainty around the considerable technical challenges.

This is no longer the case.

Figure 1: Plot of the growth of the number of for profit companies pursuing commercially viable fusion energy in a given year. It's anticipated that new companies will emerge in 2020 but this graph only reflects numbers up to and including January 2020. Data from Fusion Energy Base.

The number of companies working on fusion is increasing dramatically because of confidence in plasma physics and fusion engineering, new enabling technologies which reduce costs and improve performance, and a societal demand for baseload clean energy. The leading edge of venture capital recognizes all of these factors and they are writing checks. These VCs are betting that these trends will spur small, motivated teams to overcome the remaining challenges to fusion energy and demonstrate net energy gain, unlocking larger pools of capital to then build a working power plant.

If you're not familiar with fusion energy, this article may be helpful. Also, here's the list of companies working on fusion energy.

Let's explore each of these reasons in more detail.

Confidence in Plasma Physics and Fusion Engineering

The history of plasma physics and fusion engineering is a long and interesting one spanning over 70 years. During that time, scientists and engineers developed a mature understanding of plasma physics and built a large portfolio of experimental devices of increasing sophistication. The largest and most ambitious experimental device conceived and being built by the plasma physics community is ITER.

ITER

ITER is a $25B government funded international collaboration to build the world's largest tokamak in France. One of its goals is to demonstrate significant net energy gain around 2035. ITER does not depend on the bleeding edge of enabling technologies that fusion startups do; it will use relatively conservative and well tested technologies because that is the way to net energy gain that the plasma physics community confidently knows how to build today.

Figure 3: A cutaway illustration of the ITER tokamak. Note the person (lower right) in blue for scale. Credit ITER

ITER benefits fusion startups in a number of ways, but there are two that stand out.

First, ITER signals to investors that the major scientific questions underlying fusion energy (in particular tokamak approaches) are reasonably well understood. It signals that there is confidence among the scientific community to invest major resources in a project with a stated goal of demonstrating net energy gain. It says to the world "we believe this can be done".

Second, ITER's published engineering decisions allow fusion companies to focus their efforts on their own core designs while effectively outsourcing the development of plasma facing materials. Because D-T fusion reactions emit high energy neutrons, the development of plasma facing materials is critical and ITER shoulders much of that burden.

ITER may be to fusion startups what the Space Shuttle was to SpaceX, a government funded precursor to a commercially viable industry.

Enabling Technologies

A handful of new technologies that emerged in the 2010s is enabling smaller, cheaper designs for fusion power plants. Smaller and cheaper designs let teams iterate faster on prototypes. Here's a sampling of some of these technologies.

Magnets

In magnetic fusion approaches, very strong magnetic fields are required. They bend the trajectory of the plasma so it remains in the confined region long enough for many fusion reactions to occur.

On this front, the latest breakthrough comes in the form of a new kind of thin, flexible superconducting ribbon. This superconductor material goes by the acronym REBCO and was discovered in the 1980s (winning the 1987 Nobel Prize in physics) and commercialized into usable lengths in the 2010s. When formed into coils it simultaneously enables much larger magnetic fields and smaller machines.

Figure 5: REBCO superconducting ribbon used by fusion startup companies. When cryogenically cooled this ribbon can conduct the same amount of electrical current as a copper cable as thick as your wrist without any losses. Credit Fujikura Website

Larger magnetic fields from thinner coils enable smaller devices and lower costs. REBCO alone is responsible for the founding of more fusion energy startups than any other technology in recent years.

Lasers

A leading inertial fusion approach uses powerful lasers. The lasers fire from all directions at a solid fuel pellet of deuterium and tritium, burning off its surface outwards and as a consequence driving the remaining material towards the center.

Today, the efficiency of these lasers is low and the costs are high. At the National Ignition Facility (NIF), the most advanced facility of this type, lasers occupy entire buildings, and at most only a few shots can be fired per day.

Inexpensive and efficient diode lasers developed by the telecommunications industry may be the solution. Produced by standard semiconductor manufacturing techniques, these lasers produce high power beams while maintaining a high level of efficiency and low costs. Figure 7: Small laser diode array. Note the scale on the ruler, the device is 3 inches wide. Credit LLNL

Compared with magnetic fusion, efforts to commercialize laser inertial fusion are still early. Regardless, new diode lasers and recent progress on the scientific side from experiments like NIF have stimulated the founding of some of the newest fusion energy startups.

Electronic Switches

Magneto-inertial approaches to fusion take a pulsed approach which require high power, high speed switches. Until the mid 2000s, these kinds of switches relied on vacuum tube technology like krytrons and thyratrons, the last bastion of vacuum tubes for which there was no solid state replacement.

Driven by the requirements of the solar and wind energy industries, high power, high speed solid state switches which satisfy the demands of pulsed approaches are now commercially available. They are more robust, efficient, and reliable.

Figure 9: Solid state thyristor which replaces vacuum tube technology

While not the most exciting component of a fusion power plant (they usually live in cabinets, out of the limelight), they are quietly expanding the design parameters of magneto-inertial fusion approaches, improving performance, and reducing costs.

Computation

A list of enabling technologies for fusion energy would not be complete without mentioning the transformative effect of faster computer processors.

Computation aids a wide class of challenges in fusion, from simulating small scale turbulence in plasmas to large scale simulation of entire fusion concepts.

This image shows a simulation of the Rayleigh-Taylor instability, a common instability encountered in inertial confinement schemes. Credit LLN Miranda Website.

The most transformative effects of advanced computation are yet to come as machine learning algorithms are applied to instability mitigation, algorithmic design of fusion concepts, and optimization of operational parameters.

What It All Means: Cautious Optimism and Investment

The outcome of these developments is cautious optimism shared by the stakeholders of these companies. They understand the magnitude of the scientific and engineering challenges and believe they can overcome them.

Of course there are other challenges beyond technical ones. There's the economic challenge of applying these technologies so that the total cost over the lifetime of a fusion power plant is competitive with other sources of energy. There are social and political challenges too.

What's exciting is that all of these challenges are tractable, and the societal need is not going away any time soon. Whoever gets there first will open the doors to a powerful tool to mitigate climate change and the capture of trillions of dollars of market capitalization now ascribed to the fossil fuel industry. Exciting times indeed.