Recent Progress With Fusion Reactor Tests
These last five articles are on my blog: sites.Uci.edu/energyobserver
This is a short part of an OLLI UC Irvine lecture on Science Breakthroughs of 2021, shared with Astronomer Bob Wilson of NASA.
Quantum Fusion and the “Man Who Fell To Earth” Series.
The Showtime Series at the end of episode 3 got to the technical revelation that he and the heroine plasma physics expert, were going to bring not cold fusion, but Quantum Fusion.
Actually, all fusion is quantum, and not in just one way, but in three ways.
Fusion is basically the combination of two deuterons (proton plus neutron), to a He4 nucleus (two protons and two neutrons) with the release of 22 MeV per fusion. Normal chemical binding is around an electron volt. So this is 10 million times greater.
First of all, the binding of protons and neutrons into nuclei is roughly done by the strong force of pion exchanges, or quarks and gluons binding by gluon exchange. This also provides most of our mass, since the colored quarks and gluons are bound or confined into a colorless nucleus. This binding forms a bound state with non-zero energy and internal momentum.
Now the three forms of hydrogen nuclei all have a single positively charged proton, and zero, one or two neutrons, and are called protons, deuterons, or tritium. In a plasma, the repulsive electronic force keeps them apart from fusing from the attractive but 10^-5 angstrom nuclear force range and nuclear sizes. The gas of nuclei has to be heated to 100 million degrees Kelvin or C, so that even the tail of the Maxwell-Boltzmann velocity distribution will supply a few highest speed atoms to possibly fuse.
But even that is not enough to pass over the repulsive Coulomb barrier. The nuclei have to rely on quantum tunneling to cheat their way through the Coulomb barrier that they scale. The center of the sun is at 27 million degrees C to even allow this to occur so slowly that the sun will still be around another 4.5 billion years.
But how did the deuterons form originally? They came from a Big Bang equilibrium through the quantum process of a proton converting to a neutron through the capture of an electron.
We know now that this occurs through the weakly coupled and short range virtual exchange of a high mass (80 GeV) W boson quantum process:
The neutral neutron then strongly binds to a proton to form a stable deuteron.
Now deuterons are larger than single protons, so it is easier to get two deuterons to merge under the strong force, than two protons. And tritium is even larger, so most man-made fusion starts with more abundant deuterons plus rare tritium nuclei.
The fusion of deuterium and tritium gives a He4 nucleus and a neutron, releasing 17.6 MeV of energy. The He4 nucleus carries 3.5 MeV, and the neutron carries away 14.1 MeV.
With the numbers given, the total energy input is 3 kWh, or the energy to run your microwave for three hours. Vice-versa, if breakeven fusion is obtained, it will generate that much energy after using that much energy.
Tritium decays with a half-life of 12.5 years, or at 5.5% a year. It is made by cosmic rays. There was also a large production in nuclear weapons testing. Current tritium is made through control rods which contain Lithium-6 and are exposed to reactor neutrons, in a TVA nuclear reactor.
A concept for a working Inertial Confinement Fusion reactor would drop in 16 new hohlraum cavities each second, with each laser pulse causing 2 megajoules of fusion energy output. At that rate, the overall output would be about a GigaWatt, comparable to the standard US nuclear reactor.
The lasers used are Neodymium phosphate glass. They are all brought to the excited state by 7,680 flash lamps powered by capacitors which build up the charge over 30 seconds. Comparing that to the needed 16 flashes and discharges a second for the concept working fusion reactor, is short by a factor of 500. The laser discharge is in the infrared at 1,053 nanometers, or 1.18 electron volts. Optically, this is triply boosted to 3.5 electron volts in the ultraviolet before being sent into the hohlraum.
Besides heating the deuterium-tritium plasma, higher pressure guarantees more collisions per second to fuse. The ablation of the hohlraum and the heating of the surface of the deuterium-tritium capsule generates a 400 billion atmospheres pressure at the center.
While the output 2 megajoules from fusion is six times the kinetic energy input, it is also equal to the amount of laser energy input. However, the flash lamps which excite the lasers are inputting 330 megajoules of energy at a 100 million amps. So in terms of energy input to the whole system, it looks like the 2 megajoules out from each firing is short by a factor of 165.
The National Ignition Facility is at the Lawrence Livermore National Lab at Livermore, California, 45 miles East of San Francisco. The NIF uses 192 laser beams in a 10 story building covering three football fields in length to deliver 2 million joules in billionths of a second pulses.
The NIF achieved fusion three times over 2021 which was the breakthrough, after starting in 2009. The best was the August 8 shot that gave 1.38 megajoules. Another was 0.43 megjoules, and lastly 0.70 megajoules.
Besides the enormous $25 billion world collaboration of ITER in Europe, there are several companies including our local TAE Technologies who are hoping for breakthroughs. TAE is backed by Google including its computer power, and hopes to achieve fusion by 2025.
In episode 5 of “The Man Who Fell to Earth”, Faraday has the brilliant breakthrough that looks somewhat like the Tokamak or ring design for the UK Spherical Tokomak for Energy Production (STEP) fusion reactor below. This will be designed for a few hundred megawatts output when built. While the National Ignition Facility has been researching for over 50 years, in episode 7 of the above series, they plan to set up production in a month, and then produce a million mini reactors a year.
In a working fusion plant, the neutron would get absorbed by a lithium 6 blanket, giving up its energy as heat, and producing another tritium nucleus to be reused in the plant.
For completeness, we include the processes by which the sun achieves fusion. First, through proton collisions to form Deuterium, then adding another proton to form Helium-3. Finally, two Helium-3 nuclei fuse to form Helium-4 and two protons.
