  Nuclear fusion offers the potential for being a near limitless energy source
by fusing together deuterium and tritium nuclei to form helium inside a plasma
burning at 100 million kelvin. However, scientific and engineering challenges
remain. This paper describes how such a plasma can be confined on Earth and
discusses the similarities and differences with fusion in stars. It focusses on
the magnetic confinement technique and, in particular, the method used in a
tokamak. The confinement achieved in the equilibrium state is reviewed and it
is shown how the confinement can be too good, leading to explosive
instabilities at the plasma edge called Edge Localised modes (ELMs). It is
shown how the impact of ELMs can be minimised by the application of magnetic
perturbations and discusses the physics behind the penetration of these
perturbations into what is ideally a perfect conducting plasma.
