The holy grail of sustainable energy
is nuclear fusion. This is a potentially inexhaustible source and it has no dangerous side-effects. Fusion causes no poisonous radiation. There are no emissions of carbon compounds, or any other pollutants.
This is the process by which stars generate energy.
Atoms of some element are squeezed to fuse into a heavier element. Some leftover particles are released and converted into energy.
The commonest stellar reaction squishes hydrogen (the lightest and most abundant element) till it forms helium (the second-lightest element). Stars also squeeze helium and other elements to create successively heavier elements — this is how all the elements are formed.
There is a not-so-small catch, however. Triggering fusion reactions requires the same heat and pressure as occurs within stars. This means temperatures of 100 million degrees Celsius, and pressures of 100 billion Earth atmospheres.
One way is to set off carefully-shaped nuclear devices. We learnt to make big bangs a long time ago but unfortunately, this is dirty, destructive energy. First, a nuclear fission explosion — an atom bomb —is set off. Fission splits atoms of an element (normally uranium or plutonium) into atoms of a lighter element, releasing energy via excess particles.
A fission explosion creates stellar conditions for a brief instant. That triggers an explosive fusion reaction, if fusion material is stored in exactly the right place. The subsequent fusion explosion releases vastly greater quantities of energy in a second explosion.
This method of generating fusion energy is often called a hydrogen bomb, though it’s properly known as a thermonuclear bomb since it doesn’t necessarily involve hydrogen. It is very effective if the objective is to wipe out vast populations. The fission explosion also releases lethal radiation that may last for millennia.
A more usable form of fusion would require a less destructive trigger, and it would release fusion energy in a controlled, usable format. This involves somehow tightly confining fusion material and gradually applying heat and pressure.
There are a few ways to do this. One is to create a very powerful magnetic field, which confines the fusion material. One of the geniuses who designed thermonuclear explosive devices, Andrei Sakharov, also pioneered magnetic confinement designs. These things are called Tokamaks (Russian for “doughnut” due to the shape of the magnetic field). Another method is inertial confinement, where fusion material is stored inside a physical capsule, which is squeezed.
Both methods work: They trigger fusion generating controllable energy rather than explosions, and they don’t cause radiation. The catch is, awful amount of energy is required. Creating a Tokamak’s magnetic fields and sustaining it, or bombarding an inertial containment capsule, takes insane energies. The energy output is much less than the input, which rather defeats the purpose.
Scientists have been trying to tweak these designs since the 1960s to find ways to put less energy into triggering fusion, or to extract more energy. Every so often, a “fundamental breakthrough” is announced and it usually turns out to be a disappointment. As a result, sceptics joke that working nuclear fusion has always been estimated to be “just” 30 years away, for all of the last 60 years.
Despite the multitude of disappointments, the latest breakthrough does look promising. Physicists at the National Ignition Facility, Lawrence Livermore National Laboratory, in Livermore California, generated nearly as much energy as they put into an inertial confinement system. They claim to have generated 8x as much as similar experiments done only six months ago.
They used an ingenious design, which put deuterium and tritium (unstable forms of hydrogen) inside a gold capsule that acts as a hohlraum. A hohlraum turns radiant energies into X-rays, captures them and bounces them around inside the capsule. The experiment blasted the hohlraum with 192 high-energy lasers. The energy input was 1.9 megajoules (MJ) and output 1.3 MJ.
The average American consumes 300,000 MJ/ year while the average Indian consumes 24,000 MJ. Scaling up this experiment to meaningful levels, and making the energy equation favourable could still be many years away. But maybe, it really is just 30 years or less.
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