|Source: ZME Science|
For the last 70 years, nuclear fusion has always been 20 years away. But maybe for the first time we might get it.
Most nuclear power comes from nuclear fission--heavy molecules like uranium or plutonium are split into lighter molecules and the process releases energy. Alas, it also releases some very toxic by-products. For decades, the holy grail has been nuclear fusion, which involves smashing together light atoms like hydrogen and helium and their isotopes to produces heavier atoms. This is the process by which stars--including our own sun--produce energy. But it requires the incredibly high temperatures and pressures inside a star to work. The problem for nuclear fusion attempts so far has been that duplicating that high pressure and temperature here on earth has been hard. It's been done--that's what a hydrogen bomb does. But to do it safely and produce more energy out than we put in has so far eluded us.
Previous attempts to recreate the temperature and pressure inside a star's heart involved a tokamak--a ring which contains the superhot plasma inside a magnetic field in the shape of a torus. The new technique, invented by an Australian scientist at the University of New South Wales, involves used very short ultra-powerful laser bursts to set off a cascading reaction.
The new hydrogen-boron reactor is potentially a game changer for a simple reason: efficiency.[Read more here]
A deuterium-tritium reactor faces two challenges on the way to producing electricity: A lot of the energy gets wasted as atoms shed neutrons during the reaction, and the remaining energy can't be converted directly to electricity. Instead, it's used to heat up water, which turns a turbine, which produces electricity. So, most of the energy put into the reaction can't be efficiently translated into usable electricity.
But in the new study, which was published Dec. 12 in the journal Laser and Particle Beams, Heinrich Hora, a physicist at the University of New South Wales in Australia, and colleagues argued that they can sidestep these challenges by using a completely different fusion reaction.
If you fuse hydrogen-0 (just a single proton with no neutrons or electrons) and boron-11 (a version of boron with six neutrons) to make three helium-4 nuclei (each containing two protons and two neutrons), the researchers wrote, no neutrons get wasted. The atoms combine cleanly without losing any of their core particles. And in the reactor Hora proposes, the energy of the plasma could be converted directly into electricity without wastefully heating up water along the way, because the fusion's energy is released as a stream of electrically charged particles, which can relatively easily be turned into current in a wire.
Unlike deuterium-tritium reactors, which hold superheated plasma in place using magnets inside donut-shaped chambers, Hora's spherical hydrogen-boron reactor uses lasers to trigger and sustain the reaction. Those lasers are critical, Hora said: They waste much less energy heating up the atoms in the plasma and use less energy keeping the atoms in place.
The lasers allow the hydrogen-boron plasma to reach temperatures of 5 billion degrees Fahrenheit (3 billion degrees Celsius) and densities 100,000 times greater than those of the plasmas inside a deuterium-tritium reactor. Those are much more intense reaction conditions than other projects aim for, but Hora and his team wrote that it should be easier to achieve these conditions given current technology, at least according to the researchers' early experiments and simulations.
The spherical shape, meanwhile, would allow the superhot plasma to retain a more efficient cylindrical shape at its core, which makes it an ideal target for the cylindrical laser. A spherical shape also efficiently retains the energy produced by the fusion reaction, the researchers said.
One of the brightest burning dreams of sci-fi enthusiasts the world over is closer to reality than we’ve ever dared hope: sustainable fusion on Earth. Drawing on advances in high-power, high-intensity lasers, an international research team led by Heinrich Hora, Emeritus Professor of Theoretical Physics at UNSW Sydney, is close to bringing hydrogen-boron reactions to a reactor near you.[Read more here]
Energy from scratch
In a recent paper, Hora argues that the path to hydrogen-boron fusion is now viable and closer to implementation that other types of fusion we’re toying with — such as the deuterium-tritium fusion system being developed by the US National Ignition Facility (NIF) and the International Thermonuclear Experimental Reactor under construction in France.
Hydrogen-boron fusion has several very appealing properties which Hora believes puts it at a distinct advantage compared to other systems. For one, it relies on precise, rapid bursts from immensely powerful lasers to squish atoms together. This dramatically simplifies reactor construction and reaction maintenance. For comparison, its ‘competitors’ have to heat fuel to the temperatures of the Sun and then power massive magnets to contain this superhot plasma inside torus-shaped (doughnut-like) chambers.
Furthermore, hydrogen-boron fusion doesn’t release any neutrinos in its primary reaction — in other words, it’s not radioactive. It requires no radioactive fuel and produces no radioactive waste. And, unlike most other energy-generation methods which heat water as an intermediary media to spin turbines — such as fossil-fuel or nuclear — hydrogen-boron fusion releases energy directly into electricity.
All of this goody goodness comes at a price, however, which always kept them beyond our grasp. Hydrogen-boron fusion reactions require immense pressures and temperatures — they’re only comfortable upwards of 3 billion degrees Celsius or so, some 200 times hotter than the Sun’s core.
Back in the 1970s, Hora predicted that this fusion reaction should be feasible without the need for thermal equilibrium, i.e. in temperature conditions we can actually reach and maintain. We had nowhere near the technological basis needed to prove his theory back then, however.
I have no doubt we will one day get fusion. It will be essential to our exploration of the solar system. In the mean time, back on earth, we'll continue to rely of the giant fusion reactor in the sky, via solar panels. Solar now costs under $20/MWh. But the time we get fusion, solar power will be down to below $10/MWh (1 cent/kWh). But fusion will be extremely useful on Mars, where the insolation is less than half what it is here. And if it works this time, it'll come on stream just when it's needed.
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