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Realizing nuclear fusion as a practical energy source poses enormous challenges owing to the extreme physical conditions required by the known fusion reactions. These include temperatures of 100 million degrees Celsius or more and astronomically high pressures, which must be maintained long enough to reach a net energy output.
Efforts to achieve this goal are dominated today by expensive, large-scale experimental facilities utilizing ultra-high power lasers and microwave generators, particle beams, giant superconducting magnet systems and other advanced technologies. One might conclude that fusion, if and when it becomes a reality, will be a complex, highly capital-intensive way to produce energy.
But what if there were a much easier approach, one that would not require such elaborate technical means to achieve the extreme temperatures and pressures required? A method in which nature would do most of the work for us?
Amazingly, there does exist such an approach. It is based on a device called the dense plasma focus (DPF).
The DPF generates an electric discharge that evolves rapidly in time and space, concentrating its energy into an array of filamentary structures and finally into a tiny knot-like entity called a plasmoid (see below). Inside the plasmoid, the conditions are reached for fusion to take place. Part 2 of this series will describe in detail how it works.
The DPF has existed in various forms since the 1960s and has been utilized in dozens of university and government laboratories all over the world for experimental research in the field of plasma physics. It is also used as a source of X-rays and neutrons.
Apart from such applications, the phenomena observed in DPF discharges provide a model for a variety of self-organizing processes in nature, from the laboratory scale all the way up to the scale of galaxies and galactic clusters.
Fusion power with a plasma focus
It has long since been experimentally demonstrated that the DPF can generate large numbers of fusion reactions when operated in a chamber filled with deuterium gas.
Strangely, until recently the possibility of using the DPF for commercial power production has never been pursued with the necessary commitment and – most importantly – the financial support needed to succeed.
Nearly all investment into fusion power research today goes into funding large, expensive projects – topped off by the giant International Torus Experimental Reactor (ITER) now under construction in southern France, with a total price-tag estimated at over $40 billion.
Smaller, more innovative but less prestigious projects have been starved for funds. This situation, paradoxical to an outsider, is sadly familiar to those who have observed the behavior of funding agencies in recent decades.
The good news is that one laboratory in the United States – New Jersey’s private Lawrenceville Plasma Physics, Inc, doing business as LPPFusion – has seriously taken up the challenge to develop the dense plasma focus into a practical source of fusion energy.
There is still a way to go, but the project evidently has a real chance of success. The founder and head of LPPFusion, physicist Eric Lerner, is one of the world’s leading experts on the plasma focus and related areas of plasma physics and astrophysics.
Running on a shoestring budget with a handful of dedicated collaborators, LPPFusion has raised the performance of its DPF technology step by step, coming within striking distance of the conditions sufficient for net energy generation.
A landmark was reached in 2016 when Lerner’s device achieved an ion temperature of 2.8 billion degrees – by far the highest such temperature achieved in any fusion experiment to date. This is over 200 times hotter than the center of the sun and more than 15 times the projected maximum temperature for the ITER.
In other respects, LPP Fusion has matched or come near results obtained with devices costing hundreds of times more than the total of $7 million that LPP Fusion has spent over the last 10 years. (Here the reader can find a detailed description and comparison of the large and small fusion energy projects now underway.)
Most exciting, LPP Fusion intends to utilize hydrogen-boron instead of the standard deuterium-tritium fuel. The world-record temperatures already achieved provide an important precondition for taking this step. If the plan works out it will be extremely good news.
The hydrogen-boron fusion reaction is the dream of nuclear energy, because it generates no radioactive waste, taps a virtually unlimited supply of fuel and provides the possibility of direct conversion of fusion energy to electricity.
A single gram of hydrogen-boron mixture would produce very roughly as much energy as is released by the combustion of three tons of coal. (See my article in Asia Times, “Nuclear power’s ray of hope: hydrogen-boron fusion.”)
Fusion experiments at LPP Fusion have so far been done with deuterium. The first experiments with hydrogen-boron fuel are planned for around the end of this year.
Lerner’s project is currently in the advanced research phase. The chief task now is to move from merely producing large numbers of fusion reactions – a capability already well-demonstrated – to achieving a net energy output from the device. That will be followed by the engineering phase.
Success can never be guaranteed, of course. But the payoff would be enormous.
A low cost fusion future
DPF-based hydrogen-boron fusion power plants would combine simplicity of construction and operation with small unit size, low investment cost, low fuel cost and intrinsic safety.
For commercial power production, the DPF device is to be combined with a patented system for direct conversion of the fusion energy into electricity. Pulsed at a rate of 200 discharges per second, the system will provide an electric power output of 5 megawatts.
A complete DPF power unit would be only a few meters across, making it easy and economical to reach any desired power by simply adding more of them. The technology lends itself well to mass production of standardized units.
Plausible estimates suggest that DPF technology could reduce the cost of producing electricity by ten times or more compared with existing conventional and alternative energy technology.
Part 2: Nuclear Fusion the easy way
In Part 1 of this series, I introduced the reader to a promising innovative approach to nuclear fusion, utilizing a small, inexpensive device called the dense plasma focus (DPF).
The firm LLP Fusion, founded by plasma physicist Eric Lerner, has succeeded in producing large numbers of fusion reactions and record temperatures of 2.8 billion degrees with the DPF. In many respects, the Lerner device can compete with fusion experiments costing a hundred times more. How is this possible?
The physical principles of the dense plasma focus are well understood theoretically and have been demonstrated in countless experiments since the 1970s. Experiments reveal an astonishing complexity of phenomena in DPF discharges, characterized by self-organization and the formation of highly energy-dense structures.
The specific DPF design used by Eric Lerner consists of a pair of concentric berylium electrodes, 10 centimeters long, mounted in a chamber filled with gaseous fuel at low pressure. The outer electrode, the cathode, has an outside radius of 5 centimeters. The inner electrode, the anode, is a hollow cylinder of 2.8 cm radius.
The electrodes are connected via a fast switch to a bank of capacitors charged up to a voltage of (typically) 40,000 Volts. When the switch is closed, the capacitors send a powerful electricity pulse to the electrodes, causing an electrical discharge – a ring-shaped spark – to form between the electrodes. At its peak, over a million amperes of current flow through the device.
What exactly is this “spark”? Connecting the capacitor bank to the electrodes creates an intense electric field in the space between them. The small number of electrons that happen not to be bound together with nuclei in the gas is accelerated with enormous force toward the anode, colliding with atoms along the way and setting further electrons free.
Atoms that have lost electrons become positively charged ions and are accelerated toward the cathode, colliding with other atoms as they move. Some also collide with the electrodes, liberating more particles (mainly electrons from the cathode).
An avalanche ensues, with more and more electrons being knocked out of the atoms, creating more and more free electrons and ions and more collisions. The gas is rapidly transformed into a hot, high-energy medium consisting of freely moving electrons and ions.
This medium is what physicists term a “plasma” – sometimes called “the fourth state of matter.” Actually, most of the matter in the universe exists in the plasma state.
Now the fun starts. The flows – of electrons to the anode and ions to the cathode – constitute electric currents. Electric currents generate magnetic fields. The magnetic fields act on the electrons and ions, which in turn can change the pattern of currents.
The pinch effect
At this point, a well-known physical mechanism known as the “pinch effect” comes into play. The pinch effect provides the key mechanism by which the DPF concentrates its energy.
Put simply, the pinch effect refers to the fact that parallel electric currents attract each other. This effect is a consequence of the magnetic fields generated by the currents.
As a result, a plasma carrying a strong current will be “pinched” – compressed – perpendicular to the direction of the current.
Many approaches to nuclear fusion use the pinch effect – above all, the so-called magnetic confinement fusion devices, of which the ITER will be the largest. But there is a big difference in the methodology involved.
The pinch effect tends to produce instabilities in a plasma. But the mainline approaches to fusion, such as the ITER, pursue the strategy of trying to suppress all instabilities. They try to keep the plasma as quiet and stable as possible.
The goal is to reach a steady-state with continuous energy generation. Plasma instabilities are not merely unwelcome; they can also cause serious damage to a device.
And now for the big difference. The DPF, in contrast, exploits instabilities as the main mechanism for reaching fusion conditions. This opposite philosophy is one reason why the plasma focus has tended to be overlooked in the context of mainline efforts to realize fusion energy.
Fusion in three steps
The dense plasma focus reaches the conditions for fusion through a series of stages. The process is far too fast for the human eye – the whole discharge lasts only about two- millionths of a second – but superfast cameras and other instruments can document every stage.
Stage 1: The pinch effect causes the originally smooth plasma sheath to break up into an array of dense current filaments, running radially between the electrodes. These filaments have a characteristic vortex structure, studied in detail by the plasma physicists Winston Bostick and Vittorio Nardi beginning in the early 1970s.
Stage 2: Electromagnetic fields force the filaments to travel rapidly down the axis of the device. When the filaments reach the ends of the electrodes, they bend around in a fountain-like pattern, with filaments reaching into the inside of the hollow anode.
Inside the anode, the distance between the filaments is reduced. As their currents flow in the same direction, the pinch effect operates again, causing the filaments to attract each other. They merge together forming a single narrow filament of plasma.
Stage 3: At this point, the electromagnetic interactions cause the pinched filament to become unstable – the so-called kinking instability. The filament coils up into a helical form. Nearby windings attract each other, again by the pinch effect. Finally, the coiled filament becomes knotted up, forming a tight structure called a “plasmoid.”
Lerner’s experiments’ plasmoids are extremely small – only a fraction of a millimeter across, amounting to about a millionth of the original plasma volume.
Most of the energy of the discharge is now concentrated in this tiny space. Here the plasma is confined and compressed by super-strong magnetic fields generated by the current filaments. Inside the plasmoid, the energy of the rapidly-moving electrons and ions is transformed into heat, creating temperatures of nearly 3 billion degrees.
At these temperatures, large numbers of fusion reactions occur. The total fusion output depends on a combination of the temperature, the fuel’s density in the plasmoid and the length of time the plasmoid “lives.”
In Lerner’s experiments, the plasmoid lasts only about 10 billionths of a second. Hence a major focus of the effort is to increase the plasmoid density as much as possible. Much progress has been made, but there is still a considerable way to go as we shall see in our series’ next and concluding installment.
Part 3: A cheaper, faster way to nuclear fusion
One of the most notable features of Eric Lerner’s approach to fusion using the Dense Plasma Focus (DPF), presented in Part 1 and Part 2 of this series, lies in the possibility of using hydrogen and boron as a fuel. This property is shared by the hydrogen-boron laser fusion reactor, which I discussed in a previous series of articles in Asia Times.
Among other things, the fusion reaction between nuclei of hydrogen and boron is aneutronic: no neutrons are produced, but only charged alpha particles. This gives the DPF enormous potential advantages over the mainline fusion technologies, which are all designed to employ a mixture of the hydrogen isotopes deuterium (D) and tritium (T) as their fuel.
This includes both conventional laser fusion – typified by the National Ignition Facility in the United States – and the (estimated) US$40 billion International Torus Experimental Reactor (ITER), which has been slated as the forerunner to a future fusion power plant.
In terms of the physical conditions required, the hydrogen-boron reaction is within the potential reach of the DPF, but far beyond the mainline systems’ projected capability. It requires at least ten times higher operating temperatures than the mainline systems can hope to attain. They are thus forced to use the much “easier” D-T reaction.
Unfortunately, D-T reactions release about 80% of their energy in the form of high-energy neutrons. This leads to a whole bundle of problems.
As electrically neutral particles, neutrons penetrate easily into atomic nuclei in the surrounding materials, rendering a portion of them radioactive. In addition, the intense flux of neutrons generated can seriously damage exposed parts of the reactor.
The problem posed by induced radioactivity of reactor materials is minor compared to the radioactive waste problem of fission reactors; nevertheless, fusion power plants based on D-T fuel will require systems for handling, recycling and (most likely) medium-term storage of “activated” materials. The neutron-induced radioactivity imposes additional costs and complexities in the construction, maintenance and operation of a fusion power plant.
Perhaps even more significant is the advantage of the DPF when converting the energy output from fusion reactions into economically usable forms, above all electricity. There is currently no known practical way to convert the energy of intense neutron radiation directly into electricity.
With most of their fusion output in the form of neutrons, reactors utilizing D-T fuel must use the heat generated when the neutrons are absorbed in a suitable material surrounding the “combustion chamber.” The heat must then be transferred to cooling systems and heat exchangers, and finally used to power turbine generators.
This old-fashioned thermal power generation scheme adds enormously to the bulk and expense of a future fusion power plant.
The situation is completely different for the DPF system, which I have described in the preceding installments of this series. This system relies on natural self-organizing processes to concentrate the energy of an electrical discharge into a tiny, dense structure called a plasmoid, where the conditions for hydrogen-boron fusion can be reached.
Assuming it will be possible to obtain from the DPF a sufficient quantity of fusion reactions, how can we extract resulting energy in a usable form – as electricity? Here, again, nature works for us.
It has long been known that DPF discharges generate powerful, directed beams of electrons and ions. As it turns out, these beams originate in the plasmoid itself, at the end of its life.
At that point, a new instability occurs, which disrupts the currents in the plasmoid and gives rise to an intense electric field. Ions and electrons are accelerated to high velocities in opposite directions along the axis of the device. The ion beam contains the alpha particles released by the hydrogen-boron reactions.
Naturally, I am talking about a single, extremely short pulse rather than a continuous beam.
The technology for converting ion beams energy into electricity already exists; it is utilizated at many particle accelerator facilities. Unfortunately, only two-thirds of the plasmoid energy ends up in the ion beam. Most of the remainder is emitted from the plasma in the form of X-rays.
Here basic physics provides the solution, in the form of the so-called photoelectric effect: X-rays knock electrons out of a metal, thereby generating electric energy. LPPFusion has developed a patented X-ray conversion technology exploiting this principle.
From the total electrical energy produced, part goes to recharge the electrical capacitors that supply the discharge and to cover the consumption of various auxiliary systems. The remainder goes as net output to the electric grid, to industrial processes, etc.
In LPPFusion’s projected DPF power plant, the discharge-recharge cycle would be repeated 200 times per second, reaching a net power output of five megawatts. This assumes, of course, that the DPF will be able to generate the requisite amount of net energy from fusion reactions.
Despite its record temperatures, the DPF is still very far from achieving net energy production, which would mean more energy released by the fusion reactions than was put into the device.
Up to the work of Lerner and his group, no one had made a systematic effort to optimize the fusion output by exploiting the self-organizing process I just described. At first glance, the challenge appears daunting: to reach the goal of “breakeven”, the amount of fusion energy released per discharge will have to be increased 120,000-fold.
That sounds like a huge factor. But, as it turns out, it can be attained by a much more modest improvement in a few key parameters. Naturally there can be no guarantee, but the goal appears achievable in the relatively short-term.
Lerner and his group are pursuing a clearly defined roadmap. The key task is to increase the density of the plasmoid, above all by improving the symmetry of the array of filaments at the point they merge together and doubling the current through the device.
The expectation is to achieve the required 100-times increase in plasmoid density by the end of this year, and afterward go over to using hydrogen-boron fuel. (So far, experiments have employed deuterium.)
If all goes well, the engineering and prototype development phase could begin next year. A major advantage in time and cost lies in the fact that no big scale-up of the device will be required. The commercial version of the DPF will have essentially the same dimensions as the present experimental version.
Lerner has evidently succeeded in generating a significant amount of excitement around the project, to the point where a substantial part of the costs of ongoing experimental work is being raised through investment crowd-funding. There are currently over 750 investors.
That said, it is obvious that the lack of more adequate financing is the main factor holding back the project at this point.
A future article will discuss what the DPF can teach us about the Universe on the astronomical scale, including objects such as quasars and clusters of galaxies. Asia Times will also publish a future interview with Eric Lerner on the DPF project and his other scientific work.
Jonathan Tennenbaum received his PhD in mathematics from the University of California in 1973 at age 22. Also a physicist, linguist and pianist, he’s a former editor of FUSION magazine. He lives in Berlin and travels frequently to Asia and elsewhere, consulting on economics, science and technology.