Fusion group

Nuclear fusion is a reaction in which two light nuclei collide to form a single heavier nucleus. In this process a significant proportion of the mass of the reacting nuclei is converted directly in to energy. As a result of this, nuclear fusion is one of the most energetic reactions known to humanity.

As all nuclei are positively charged, there is a very strong repulsive force between two nuclei in close proximity. For a fusion reaction to occur, the two nuclei must be brought close enough together for the attractive nuclear forces to take over. This requires a very large amount of energy. When a gas is heated to thermonuclear temperatures, over 10,000 degrees, many of the particles in the gas will have the energy necessary to produce fusion. At these temperatures the nuclei and electrons of the gas have separated, forming a new state of matter called a plasma. A substantial proportion of the collisions between the energetic nuclei will result in a fusion reaction. The energy released in these reactions will heat the plasma further and hence sustain the fusion reactions occurring within it. This process occurs naturally in stars and is the fundamental source of most of the energy on the earth.

The major technological barrier to achieving commercial fusion on earth as a power source is the difficulties associated with confining a plasma at thermonuclear temperatures. Any contact by the plasma with the containing walls will result in large energy loss, which may result in a cessation of nuclear reactions and damage the walls of the containing vessel. All major approaches to developing fusion as a power source focus on addressing the problems of providing energy to the nuclei so they may fuse, and confining the hot plasma which results.

The most highly developed fusion reactor design relies on magnetic fields and a toroidal (doughnut) geometry to contain the plasma. First conceived in Russia in the 1950's, a prototype reactor of this design is currently under construction in the south of France, and is expected to produce 500 MW of power. 

The reactor vessel in which the plasma is contained is shaped like a doughnut. Wrapped around the vessel are many coils of wire, through which large currents are passed. This produces a magnetic field inside the vessel which forms a large loop around the length of the doughnut. The charged particles which compose the plasma spiral around this magnetic field and are kept from making contact with the vessel walls. A current is passed around the vessel in the plasma. This current produces a second magnetic field and heats the plasma, much like a heater element is heated by the current passing through it. This second magnetic field corrects for the drift of particles towards the walls resulting from the curvature of the first magnetic field. The combination of magnetic fields has proven highly successful in confining plasmas with temperatures over 1 million degrees. 

Difficulties arise, however, as the plasma itself creates magnetic and electric fields itself which can counteract the confining fields. These instabilities need to be closely monitored and controlled if the plasma is to remain contained. It is this for this reason that the progression to a prototype reactor has taken over 60 years since the idea's conception. Over the many decades of the reactor design's development, the size of the vessel has steadily increased, as this was found to be necessary to combat the instabilities in the plasma. As a result, operating Tokamaks will be the size of very large buildings, and there is little hope for miniaturisation of the design. 

An alternative design for a fusion reactor which holds much promise as a compact, portable fusion power source is termed Inertial Electrostatic Confinement. This design was conceived in the early 1960's but has received a fraction of the research effort that the Tokamak design has enjoyed. It is this plasma confinement method which is the subject of the research performed by the Fusion Group at the University of Sydney.