Energy Balance: UK and US Join Forces on Laser-Fusion Energy.

Monday, September 12, 2011

UK and US Join Forces on Laser-Fusion Energy.

The UK company AWE and the Rutherford Appleton Laboratory have joined-forces with the US-based National Ignition Facility (NIF) to help provide energy using Inertial Confinement Fusion, in which a pellet of fuel is heated using powerful lasers. Since the late 1950s, UK scientists have been attempting to achieve the fusion of hydrogen nuclei (tritum and deuterium) using magnetic confinement (MCF). The Joint European Torus (JET) is located in Britain, which is the largest such facility in the world and may be regarded as a prototype for the International Thermonuclear Experimental Reactor (ITER) based in France.

So far, the "breakeven point" has not been reached, and the energy consumed by the plasma has yet to yield more energy than it takes to maintain it; moreover, there are problems of instability, meaning that plasmas tend to collapse within fractions of a second when they must be maintained over significant periods if, e.g. they are to be used to provide a constant output of energy as in a power-station of some kind.

An alternative is Inertial confinement fusion (ICF), in which fusion of nuclei is initiated by heating and compressing a fuel target, typically in the form of a pellet containing deuterium and tritium contained in a device called a hohlraum (hollow space or cavity) using an extremely powerful laser. Energy is delivered from the laser to the target, causing its outer layer to explode, which drives the inner substance of the target inwards, compressing it massively. Shock-waves are also produced that travel inward through the target.

If the shock-waves are intense enough, the fuel at the target centre is heated and compressed to the extent that nuclear fusion can occur. The energy released by the fusion reactions then heats the surrounding fuel, within which atomic nuclei may further begin to fuse. In comparison with "breakeven" in MCF, in ICF a state of "ignition" is sought, in which a self-sustaining chain-reaction is attained that consumes a significant portion of the fuel. The fuel pellets typically contain around 10 milligrams of fuel, and if all of that were consumed it would release the energy equivalent to that from burning a barrel of oil. In reality, only a small proportion of the fuel is "burned". That said, "ignition" would yield far more energy than the breakeven point.

At the NIF it is hoped to have ignition within a couple of years, or far sooner than the carrot-before-the donkey "50 years away" for MCF, although there is much to be done yet. A single shot from the world's most powerful laser at NIF is reported to have released "a million billion neutrons" and for a tiny fraction of a second produced more power than was being consumed in the entire world, although to achieve ignition this would need to be increased a thousand-fold.

A real breakthrough, no doubt. But as with MCF, how long before this technology can be fabricated into actual power stations? There are many nontrivial ancillary challenges too, especially the secondary procedure of actually getting the energy out of the reactor into a useful form, i.e. heat to drive steam-turbines as with all other kinds of thermal power stations, to generate electricity. This is very complex and untested technology compared, say, to coal- and gas-fired or nuclear power plants. Actual fusion power is still at best many decades away and the concept should not be thrown as a red-herring that the world's impending energy crisis has been abated.

Most immediately, what fusion in any of its manifestations does not address is the problem of providing liquid fuels as conventional supplies of oil and gas decline, and it is this which is the greatest and most pressing matter to be dealt with, against a backdrop of mere years not a luxury of decades.