Fusion is the process of fusing two particles together to form new ones. If the mass of the products is less than the mass of the two fusing particles then, by Einstein's famous E = mc2
equation, energy will be released during the nuclear reaction. This process occurs naturally under the extreme plasma conditions at the centre of the Sun and all stars, meaning that achieving fusion here on Earth is a rather tricky challenge, but one which holds the key to electricity provision for the truly long term.
If realized, fusion energy can provide a clean, safe, and economic source of energy for over a million years. The fuel materials are deuterium (extracted from sea water) and tritium (which can be produced from Lithium), which are isotopes of hydrogen and highly abundant on Earth. At temperatures of a hundred million degrees, deuterons and tritons can collide and fuse to produce an alpha particle and a highly energetic neutron. Stopping of these neutrons in a "blanket" around the plasma allows energy extraction which is used to turn turbines and generate electricity.
The key question is: how one can create such a high temperature plasma and still obtain net energy gain from the reaction?
One route to achieving this is called inertial confinement fusion (ICF). The central idea of ICF is to use lasers to heat the exterior of a deuterium-tritium spherical shell. The resulting rocket effect leads to an implosion that creates a very dense (10000 fold increase in density) deuterium-tritium mass. In principle a hot spot will also be created that will ignite the fuel, causing it to burn up through fusion reactions before the fuel can expand out again. Theoretically this should lead to net energy gain.
A variant on this concept is Fast Ignition ICF. In this concept an implosion produces a very dense mass of deuterium-tritium fuel, but without a hot spot. A hot spot is then generated separately by sending in a laser-generated relativistic electron beam. In principle this should lead to very big savings in the scale of the lasers required to drive the implosion leading to cheaper ICF, and also leading to higher gain factors at the same time.
The VULCAN PetaWatt (link opens in a new window) laser is an ultra-intense laser capable of generating relativistic electron beams, although it is of a smaller scale than that needed for ignition. It can be used to study the basic physics of relativistic electron beam propagation in dense plasmas which is a critical issue in Fast Ignition research, see here (link opens in a new window) for examples.
The European-led HiPER project (link opens in a new window) is dedicated to demonstrating laser driven fusion as a future energy source.