Terrestrial Fusion [1]
The concept of fusion is at the heart of star formation, the same energy source as that which powers our sun. Similar principles are involved in fusion here on earth: two atomic nuclei, stripped of their electrons, can fuse only when they get close enough, for long enough, that the attraction of the strong nuclear force between them overcomes the Coulomb electrostatic repulsion of the protons. When this happens the ions merge to form a single nucleus of a heavier element that has less mass than the ingredients did: the lost weight is multiplied by the speed of light squared into a massive amount of energy: E=mc² By way of contrast, fission reactors harness energy from atoms such as uranium that are falling apart rather than joining together [2].
Why fusion? The aspiration behind mankind’s current interest in fusion is no-risk inexpensive clean energy, pithily expressed in a few quotes:
- “a few kilograms could power a small city for a year with no greenhouse gases, and its waste is balloon-ready helium” [3];
- “Towards the end of the century, we don’t know where the hell our energy’s going to come from, and while renewables will do some of that they won’t do all of that” [4];
- “Fusion will end wars, solve global warming and make you a nice cup of tea afterwards” [5]
- “And a fusion generator cannot melt down like current nuclear fission reactors[6]. There is no chance of a Fusion Chernobyl or Fusion Fukushima” [7].
How does it work?
The main fuel available for exploitation is deuterium, the heavy version of hydrogen, which is available in plentiful supply here on earth as seawater. Current research is also focussed on tritium which can give five times the energy release. However, tritium is not available naturally here on earth. It has a half-life of 12 years and so must be manufactured. One way to exploit this is to surround the reaction vessel with a blanket of lithium which will absorb the emitted neutrons. The basic idea is that when two ions such as deuterium and tritium collide at the right high speed, they fuse into a heavier element such as helium that has less mass than the two ions combined. The fusion converts the missing mass into ‘bountiful’ energy, carried away by photons and fast moving particles such as neutrons [8].
How do we confine the plasma?
The temperatures involved in the fusion process are around 150 million degrees (10 times hotter than the centre of the sun), so once a suitable fuel has been selected to provide good energy release, how do we confine the plasma? Stars use gravity.
The current preferred method of choice is magnetic. Michael Box explains:
The plasma consists of nuclei and electrons in rapid - even violent – motion, which will respond to magnetic forces. If a suitably designed and constructed magnetic field can be engineered, it will keep the plasma in check, away from the walls of the device, [squeeze it] and allow the fusion reactions to take place. This is no easy feat. The plasmas may easily develop "kinks" which can destroy the plasma by contact with the walls Powerful, and complicated, magnetic fields are employed. Superconducting materials may one day be able to supply the electric currents required more economically [9].
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An alternative method is known as inertial confinement. Again Michael Box elaborates:
The tritium fuel is placed in a 1 mm pellet or "microballoon", which is then placed at the focus of 60 laser beams, which hit the pellet with 30 kJ of UV light in a billionth of a second. The outer pellet layer is rapidly heated and evaporates, or ablates. This happens so rapidly that it exerts an inward force on the fuel (by Newton's third law), compressing it to 1000 times its original density with a pressure of a trillion atmospheres. This creates such a high density plasma that fusion reactions take place 'instantly', before electrical repulsion forces have a chance to act [10].
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This alternative to magnetic confinement is currently in its infancy and much work still needs to be done to improve its efficiency: some 99% of all energy input is wasted
The basic criteria necessary to create a suitable plasma
It takes a considerable input of energy to create a suitable plasma, and heat it to the
required temperatures, requiring satisfaction of three basic criteria: more fusion energy must be created than is required to maintain the plasma; the reaction must be able to be sustained by feeding back enough energy to power the device continuously; and thirdly enough useful energy must be capable of being extracted at reasonable cost. To achieve these objectives in order to extract useful energy from a device known as a Tokamak (explained below), the product of the plasma density (the number of nuclei per cubic centimetre) must exceed 1014 in order to achieve break-even, and the plasma temperature must exceed 100 million degrees C to achieve ‘ignition’ [11].
How is this technology currently being exploited?
By a device originally devised by the Russians called Tokamak which confines the superheated plasma containing the ions inside a toroid, or donut shaped vacuum container.
The largest current initiative exploiting this technology is ITER, a ten storey high machine under construction in Florence, Franc, by a consortium of nations: Europe, Japan, the US, Russia, China, India and Korea, which will rely on giant superconducting magnets to control a plasma burning at roughly 150 million degrees C for minutes at a time. But even here problems have been known to occur: “the plasmas in a Tokomak misbehave. The edge of the plasma flares out, scarring the generator’s interior. Or the whole plasma goes unstable, dropping from 100 million degrees to ‘’just” 10,000, emitting a tsunami of heat and magnetic energy” [12]. And even if it eventually succeeds, ITER will make no electricity. It was originally anticipated that ITER would now be up and running at a cost of $11 billion, but the projected cost is now more like $20 billion, and full operation will not commence until 2035 at the earliest [13].
And then there is the problem of turbulence. “Plasma, like the blood it’s named after, is a mixture of two fluids, and when you have fluids you have turbulence, which can however be managed: the plasma’s electromagnetic cage can be flexed, folded or spiked within microseconds to counter instabilities [14].
Nevertheless progress is being made. Scientists hope to press "the proverbial red button" and turn on the reactor in 2025, with the ultimate goal of running it at full power by 2035. If it succeeds, the payoff would be gigantic. Fusion has the potential to release much more energy than burning coal or oil or even nuclear fission, which fuels traditional nuclear power plants – and it produces no greenhouse gases or radioactive waste.[15]
Some privately-funded initiatives [16]
ITER's failure to get up and running in a timely and cost-effective manner has let to a number of smaller initiatives at the instance of private investors: Sandia National Laboratories, Tri-Alpha Energy and General Fusion, whose technological models are much less expensive and easier and faster to build. In brief, Sandia uses a technique of creating powerful magnetic fields around a small metal cylinder of cold deuterium and tritium fuel, then blasting it and ionising the fuel as it starts to implode. Tri-Alpha, on the other hand, holds a spinning plasma of boron ions and protons in place while a huge opposing magnetic field slams it for a microsecond, setting up a strong electric current inside the plasma, and General Fusion’s reactor works in pulses, beginning by shooting a plasma of deuterium and tritium down a funnel, initiating fusion for a fraction of a second, this process repeated every second, generating bursts of energetic neutrons. In this prototype, huge pistons crash against anvils that in a larger machine would fuse fuel inside a reactor core.
So much useful research is underway, and the potential rewards are manifold: “a new source of energy that doesn’t rely on the whims of the wind or sun blocked by clouds, wouldn’t require big changes to the existing electrical grid, doesn’t raise concerns about nuclear weapons, can’t melt down or irradiate surrounding communities, and might be of no more expensive after it gets going than other forms of clean energy” [17].
[1] This material is based on an amalgam of three sources: Associate Professor Michael Box’s WEA What are atoms made of? Course, Section 5, “Nuclear Fusion” , and in particular segment 5.2 (“The Box Lectures”); “Terrestrial Fusion”; W Wayt Gibbs, “The Fusion Underground – A few bold physicists – some backed by billionaires – are exploring faster, cheaper roads to the ultimate source of clean energy”, Scientific American, November 2016. 32-39 (Gibbs); and Nick Miller, Back to the Fusion – A $10 billion science experiment could change the world as we know it”, The Sun-Herald, 30 October 2016, reproduced online as “It’s true: Nuclear Fusion and Iron Man are here to save the world” (Miller): http://www.smh.com.au/world/its-true-nuclear-fusion-and-iron-man-are-here-to-save-the-world-20161027-gscqqj.html
[2] Gibbs, 35.
[3] Miller, 23.
[4] Ibid, citing Vladimir Vlasenkov, a Russian scientist, who played a key role in developing Tokamak technology in the USSR
[5] Miller, 23..
[6] For the implications of E=mc² as regards fission, see E=mc² in practice
[7] Ibid.
[8] The Box lectures; Gibbs.
[9] The Box lectures; Miller.
[10] The Box lectures.
[11] Ibid.
[12] Miller.
[13] Miller; Gibbs, 34.
[14] Miller.
[15] Clara Moskowitz, “Fusion Dreams”, Scientific American, December 2020, 63-71.
[16] See here generally, Gibbs’ cited Scientific American article, of which the below is a digest.
[17] Gibbs, concluding paragraph at 39.
The basic criteria necessary to create a suitable plasma
It takes a considerable input of energy to create a suitable plasma, and heat it to the
required temperatures, requiring satisfaction of three basic criteria: more fusion energy must be created than is required to maintain the plasma; the reaction must be able to be sustained by feeding back enough energy to power the device continuously; and thirdly enough useful energy must be capable of being extracted at reasonable cost. To achieve these objectives in order to extract useful energy from a device known as a Tokamak (explained below), the product of the plasma density (the number of nuclei per cubic centimetre) must exceed 1014 in order to achieve break-even, and the plasma temperature must exceed 100 million degrees C to achieve ‘ignition’ [11].
How is this technology currently being exploited?
By a device originally devised by the Russians called Tokamak which confines the superheated plasma containing the ions inside a toroid, or donut shaped vacuum container.
The largest current initiative exploiting this technology is ITER, a ten storey high machine under construction in Florence, Franc, by a consortium of nations: Europe, Japan, the US, Russia, China, India and Korea, which will rely on giant superconducting magnets to control a plasma burning at roughly 150 million degrees C for minutes at a time. But even here problems have been known to occur: “the plasmas in a Tokomak misbehave. The edge of the plasma flares out, scarring the generator’s interior. Or the whole plasma goes unstable, dropping from 100 million degrees to ‘’just” 10,000, emitting a tsunami of heat and magnetic energy” [12]. And even if it eventually succeeds, ITER will make no electricity. It was originally anticipated that ITER would now be up and running at a cost of $11 billion, but the projected cost is now more like $20 billion, and full operation will not commence until 2035 at the earliest [13].
And then there is the problem of turbulence. “Plasma, like the blood it’s named after, is a mixture of two fluids, and when you have fluids you have turbulence, which can however be managed: the plasma’s electromagnetic cage can be flexed, folded or spiked within microseconds to counter instabilities [14].
Nevertheless progress is being made. Scientists hope to press "the proverbial red button" and turn on the reactor in 2025, with the ultimate goal of running it at full power by 2035. If it succeeds, the payoff would be gigantic. Fusion has the potential to release much more energy than burning coal or oil or even nuclear fission, which fuels traditional nuclear power plants – and it produces no greenhouse gases or radioactive waste.[15]
Some privately-funded initiatives [16]
ITER's failure to get up and running in a timely and cost-effective manner has let to a number of smaller initiatives at the instance of private investors: Sandia National Laboratories, Tri-Alpha Energy and General Fusion, whose technological models are much less expensive and easier and faster to build. In brief, Sandia uses a technique of creating powerful magnetic fields around a small metal cylinder of cold deuterium and tritium fuel, then blasting it and ionising the fuel as it starts to implode. Tri-Alpha, on the other hand, holds a spinning plasma of boron ions and protons in place while a huge opposing magnetic field slams it for a microsecond, setting up a strong electric current inside the plasma, and General Fusion’s reactor works in pulses, beginning by shooting a plasma of deuterium and tritium down a funnel, initiating fusion for a fraction of a second, this process repeated every second, generating bursts of energetic neutrons. In this prototype, huge pistons crash against anvils that in a larger machine would fuse fuel inside a reactor core.
So much useful research is underway, and the potential rewards are manifold: “a new source of energy that doesn’t rely on the whims of the wind or sun blocked by clouds, wouldn’t require big changes to the existing electrical grid, doesn’t raise concerns about nuclear weapons, can’t melt down or irradiate surrounding communities, and might be of no more expensive after it gets going than other forms of clean energy” [17].
[1] This material is based on an amalgam of three sources: Associate Professor Michael Box’s WEA What are atoms made of? Course, Section 5, “Nuclear Fusion” , and in particular segment 5.2 (“The Box Lectures”); “Terrestrial Fusion”; W Wayt Gibbs, “The Fusion Underground – A few bold physicists – some backed by billionaires – are exploring faster, cheaper roads to the ultimate source of clean energy”, Scientific American, November 2016. 32-39 (Gibbs); and Nick Miller, Back to the Fusion – A $10 billion science experiment could change the world as we know it”, The Sun-Herald, 30 October 2016, reproduced online as “It’s true: Nuclear Fusion and Iron Man are here to save the world” (Miller): http://www.smh.com.au/world/its-true-nuclear-fusion-and-iron-man-are-here-to-save-the-world-20161027-gscqqj.html
[2] Gibbs, 35.
[3] Miller, 23.
[4] Ibid, citing Vladimir Vlasenkov, a Russian scientist, who played a key role in developing Tokamak technology in the USSR
[5] Miller, 23..
[6] For the implications of E=mc² as regards fission, see E=mc² in practice
[7] Ibid.
[8] The Box lectures; Gibbs.
[9] The Box lectures; Miller.
[10] The Box lectures.
[11] Ibid.
[12] Miller.
[13] Miller; Gibbs, 34.
[14] Miller.
[15] Clara Moskowitz, “Fusion Dreams”, Scientific American, December 2020, 63-71.
[16] See here generally, Gibbs’ cited Scientific American article, of which the below is a digest.
[17] Gibbs, concluding paragraph at 39.