Alternative approaches: concept improvements in magnetic fusion research

While the conventional tokamak, as embodied in JET, is the front-runner in the magnetic-confinement approach to fusion, other concepts are being devel oped that might, in the long term, prove more attractive for power generati on ('concept improvement' research). Also, in the shorter term, these conce pts might offer a more-rapid and cheaper way of studying ignited or near-ig nited plasmas. Their advantages, and disadvantages, are described. The stel larator offers steady-state operation at the cost of coil complexity, new a dvanced stellarators with overall size comparable to JET are either under c onstruction or being commissioned in Japan and Germany. 'Spherical-torus' c onfigurations, of which the most promising is currently the spherical tokam ak, offer high-pressure containment in a compact device, but the high power density may mean power-plant technology will be more challenging (e.g. sui table materials). New spherical tokamaks will soon come into operation in t he UK, USA and Russia and will test properties in larger higher-current lon ger-pulse plasmas. Meanwhile, other concepts such as the 'reversed-field pi nch', magnetic-mirror systems and the dense Z-pinch, have their own advanta ges, though they are less well developed. The status of the various concept s are summarized as are their potential fusion applications that include el ectricity generation, acting as a fusion neutron source, and providing a dr iver for inertial fusion.