For decades we have been beguiled by the idea that fusion will be the miracle solution to our quest for cheap, limitless, clean energy. Here is an excerpt from a 2016 article from the Princeton Plasma Physics Lab:
“For centuries, humans have dreamed of harnessing the power of the sun to energize our lives here on Earth. But we want to go beyond collecting solar energy, and one day generate our own from a mini-sun. If we’re able to solve an extremely complex set of scientific and engineering problems, fusion energy promises a green, safe, unlimited source of energy.”
Over the past 60 years as technology has extended our reach, the number of fusion projects has proliferated. They use a variety of technologies, but one thing most of them have in common is the use of an intensely hot plasma (matter whose atoms have been stripped of their electrons) which must be maintained as long as the reactor is producing energy. The heat required is so high (150 million degrees kelvin; ten times hotter than the core of the sun) that managing it is far more difficult than anyone had imagined, and that is why it seems to be an ever-receding target, always just 20 years away. The mind-boggling figures that are required to describe ITER, the world’s largest fusion project, is a testament to both how difficult it is and to how obsessed we are with this solution. (You can read a short description of ITER in the appendix.)
Famously, railroad companies of the 19th century faded in the 20th when the internal combustion engine came along because management thought they were in the railroad business, not the transportation business. In trying to build ever bigger and more complex fusion reactors, are we stuck in the plasma business rather than in the energy business? Plasma is not the goal; it is one means to an end.
There is one company working on a process to produce energy from nuclear fusion, but without the hot fiery ball of plasma. This is HB11 Energy Proprietary Limited, an Australian company which just incorporated in 2019. The process is the brainchild of Professor Emeritus Heinrich Hora, the venerable figure who, now in his 80’s, is still actively working on what has been a lifelong dream – perfecting a fusion design that actually works.
Hora got the idea in the 1960’s when the first functioning laser inspired him to begin his dogged pursuit. He believed that with a sufficiently powerful laser, you could fuse the hydrogen nucleus (H) with the boron11 atom (B11) to efficiently produce more energy than you consumed. (The company’s name – HB11 – is a combination of the chemical signs for hydrogen and boron11.) Unfortunately, lasers at that time were far too weak to do the job, but Hora and colleagues continued their theoretical research and over the years they and others authored many peer review papers which found no obstacles to the theory.
Then came 1985 and the invention of the Chirped Pulse Amplification Laser (CPA) by Donna Strickland and Gérard Mourou at the University of Rochester. (They received the Nobel Prize in Physics in 2018 for their work.) This new technique amplified ultrashort laser pulses. This development led to progressively stronger lasers. In March 2020 a laser at the Extreme Light Infrastructure for Nuclear Physics (ELI-NP) project in Romania reached 10 petawatts, making it the most powerful laser on the planet. (A petawatt is one quadrillion watts.) This is certainly a milestone, but the pulse time was on the order of only 20 femtoseconds (quadrillionths of a second). This is too short for the HB11 reaction the to achieve significant burn. Calculations indicate that the laser intensity must be maintained for picoseconds (trillionths of a second, or ~1000 times longer). It is just a matter of time before this is reached.
In the meantime, the advent of these extremely powerful lasers has finally made it possible to test Professor Hora’s ideas in the lab. The HB11 reaction has been known for many years and produces alpha particles, helium nuclei with two protons and two neutrons. Over the years a succession of experiments driven by high power lasers were conducted to measure if alpha particles were produced and if so, how many. Here is a record of the tests:
|Test #||Location||Year||# alpha particles produced|
As you can see, as lasers become stronger, more and more alpha particles are generated. These tests are at insufficient power and duration to produce more energy than they consume, but they do show that the HB11 reaction is achieved and may benefit from a strong avalanche or cascading effect in which alpha particles collide and give energy to other protons, enabling them to create further reactions. This multiplier effect appears to be larger than what scientists had theorized, which is good because it could be the key to ultimately generating more energy than is put into the system.
Now let’s take a look at the process.
Note that the graphic uses only one atom of boron and therefore doesn’t show the cascade. The reader can imagine the process.
The red and purple bar represent the fuel. Red is hydrogen and purple is boron11. When the laser strikes the fuel, it collides with hydrogen atoms and drives them into the boron11 atoms. The laser pulse is so powerful that it sets up a supersonic shockwave that drives a localized detonation (explosive combustion) of the fuel so quickly that it doesn’t have a chance to heat the surrounding atoms.
In the title I described this process as non-thermal, but the reacting atoms are in a plasma state – they’re hot. So strictly speaking it is not non-thermal, but since only the reacting atoms get hot, the temperature of the overall system stays low, and it is from this standpoint that I call it non-thermal. And it is only when the entire fuel load becomes a plasma that you have the heat management issues that seem so intractable with other designs. This process is called non-equilibrium heating because the reacting atoms are at temperatures far greater than their neighboring atoms. You could say it’s a way of having your cake and eating it too. You just have to strike hard and fast.
Perhaps another analogy using incandescent lights and LED lights would be helpful here. Incandescent lights work by heating a filament to a high enough temperature that it glows. It heats up a lot of atoms which takes a lot of energy, and only a small amount of that energy is converted to light. LED lights pass an electric current across a semiconductor to trigger an electroluminescent process. In this case, all the atoms that are activated by the current give off light, which is a more focused and efficient way to do it than heating up all the atoms in a metal filament. The incandescent bulb is like the plasma-based reactor because it heats up all the atoms in the fuel. The LED bulb is like the HB11 reactor because only the atoms that are generating energy are heated up. It’s not a perfect analogy, but perhaps it will help you understand the distinction.
One critic of the process said that the HB11 reaction has the lowest maximum probability of fusion events per collision of all proposed fuels. This would be bad if it were true. It only applies to lower energies, the energy levels with which the critic is probably familiar. At the higher proton energies that can be created when you reach 10 petawatt for picoseconds, the physics changes and the reaction actually has a higher maximum probability of fusion events per collision than deuterium and tritium. This is also known as the cross-section.
One other important thing to note about the HB11 reaction is that it does not produce free neutrons, which means that it produces virtually no radiation. There is always some small amount of radiation when dealing with highly energetic reactions due to the vagaries of the world at the atomic level, but light shielding is all that would be needed to provide a safe working environment for the employees.
Once the reaction has produced alpha particles you need to produce electricity. Because the alpha particles have a positive charge, a device will be needed to collect them and convert the positive current into the normal negative current (electrons). Research on this topic has been underway at other organizations for years. The key here is that since you have charged particles, the potential for directly generating electricity from them is good. This avoids the lengthy and inefficient process of heating water to create steam to turn a turbine to drive a generator to produce electricity.
Going forward, HB11 Energy’s goal is to better understand the initiation of the HB11 reaction by ultrahigh power lasers. As lasers continue to get more powerful and approach the levels required for operation, the information needed to design the reactor components will become more precise and detailed. And now that HB11 Energy is a business, it can begin to raise money to conduct its own tests. Until now all these tests have been conducted at universities or government sites.
A caveat. There is the possibility that research will find that the HB11 reaction does not produce sufficient gain to be a practical energy source. That’s always true when doing cutting edge research, as this is. But I think we can share some optimism on this front in light of the fact that, after decades of research, no showstoppers have been found.
Like all other fusion projects, this one does not offer immediate relief, and immediate relief is what we need to avoid a catastrophic second half of the century. But what this unique approach does offer is engineering feasibility. Once the physics are worked out, the prospect of rapidly and relatively inexpensively building and deploying many of these reactors is good. They will be far smaller than any other power plants producing large amounts of energy, and they won’t produce emissions or radiation. This means that they could be safely housed in urban areas, which would eliminate the need for long distance, high voltage transmission and the energy losses associated with it. It would be a game changer. Perhaps until we have HB11 reactors, the solution will be compact fission reactors of the kind used on nuclear powered aircraft carriers.
Stay tuned. There’s more to come.
ITER – The International Thermodynamic Experimental Reactor
ITER is a multinational project to build the world’s largest thermonuclear fusion reactor. It uses deuterium and tritium. Construction began in 2014. Ignition is planned for 2025 followed with 10 years of research and development to achieve targeted net energy production by 2035. ITER is the poster child for how complicated and expensive thermonuclear fusion projects can become.
Everything about the ITER installation is gargantuan*. The fusion reaction will occur in a vacuum vessel within the world’s largest tokamak, an 8,000-ton stainless steel, toroidal plasma containment structure with a volume of 9,000 cubic feet. It will be lined with 440 blanket modules covering 6,458 square feet to protect the vessel from radiation and heat. It will be surrounded by 10,000 tons of superconducting magnets that will heat and control the plasma. There will be a divertor at the bottom which will control the exhaust waste gas, remove impurities and recycle unburned fuel. The divertor will consist of 54 10-ton segments for a total weight of 540 tons. The tokamak, blankets, magnets, and divertor will be surrounded by a cryostat, the largest stainless-steel high-vacuum pressure chamber ever built, weighing 3,850 tons. It will provide a vacuum environment for the operation of the components surrounding the vacuum vessel. With a pump volume of 50,000 ft³ per hour for the cryostat and 20,000 ft³ per hour for the vacuum vessel, these structures count among the largest vacuum systems ever built. Altogether the tokamak and its adjunct machinery will consist of one million components and ten million parts and will weigh around 23,000 tons.
* And expensive. Budgeted for $20B, cost overruns have already pushed expenditures to nearly $30B.
And that’s not all. The tokamak assembly will be cooled by water flowing at up to 500 cubic feet per minute through 37 miles of pipes and dozens of pumps, filters and heat exchangers to a 65,000 square foot heat rejection facility housing ten cooling cells. As hot water enters each cooling cell it will be sprinkled by a set of 4,540 spray nozzles onto a stack of corrugated plastic sheets called “fill pack.” (If unfolded, the total exchange surface provided by the fill pack would be around 7.5 million square feet, the equivalent of some 156 football fields.)
The plasma is initially heated by the ohmic effect of the containment magnetic fields which induce a current in the plasma. The plasma resists the flow of electricity, which causes heating. In a plasma, particles do not interact directly. Instead they have Coulomb collisions in which they interact on much longer ranges through their electric fields. As the temperature of the plasma increases, the speed of the particles increases, and as particle speed increases the effect of the Coulomb collision decreases. As a result, the effectiveness of ohmic heating declines as plasma temperature increases and supplemental heating is required to get the plasma to a level for a self-sustaining fusion reaction.
The ITER Tokamak will rely on three sources of external heating that work together to provide the input heating power of 50 MW required to bring the plasma to the temperature necessary for fusion. These are neutral beam injection and two sources of high-frequency electromagnetic waves.
The neutral beam injectors will shoot uncharged high-energy deuterium atoms into the plasma where they will transfer their energy to the plasma particles by colliding with them, thus heating the plasma. Before injection, deuterium atoms must be accelerated outside of the tokamak to a kinetic energy of 1 megaelectron volt (MeV). Since only particles with a positive or a negative charge can be accelerated by an electric field, the process will create negative ions by adding an electron to the deuterium atoms before accelerating them. After acceleration and before injection, the extra electron is removed so only neutral particles go into the plasma.
Neutral beam fueling will be achieved by injecting pellets of frozen fuel into the plasma. An extruder will punch out several millimeter-sized deuterium-tritium ice pellets that will be propelled by a gas gun at speeds of up to 22,000 mph. Pellet injection will be used to get the reaction to ignition, to provide steady state supply of deuterium and tritium, and to mitigate the impact of Edge Localized Modes (ELMs), energetic bursts of plasma which escape the magnetic field and cause loss of energy. Special technology is being developed to allow these pellets to fly along curved trajectories, thereby attaining specific zones within the plasmas where ELMs are particularly disruptive.
Electricity requirements for the ITER plant and facilities will range from 110 MW to up to 620 MW for peak periods of 30 seconds during plasma operation. This is where the ITER process stops, but in a commercial fusion reactor, the energy produced must be harnessed to drive turbines to power generators to create electricity.
As you can see, the technological and engineering demands of the thermonuclear fusion of deuterium and tritium are overwhelming, which is why other approaches are being investigated.