Recent Progress On Spherical Torus Research
Authors: Masayuki Ono and Robert Kaita
Abstract:
The spherical torus or spherical tokamak (ST) is a member of the tokamak
family with its aspect ratio (A = R0/a) reduced to A ~ 1.5, well below the normal tokamak
operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β
(radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as
β ~ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also
increases rapidly. Because of the above, as well as the natural elongation κ, which makes
its plasma shape appear spherical, the ST configuration can yield exceptionally high
tokamak performance in a compact geometry. Due to its compactness and high
performance, the ST configuration has various near term applications, including a
compact fusion neutron source with low tritium consumption, in addition to its longer
term goal of attractive fusion energy power source. Since the start of the two megaampere
class ST facilities in 2000, National Spherical Torus Experiment (NSTX) in the
US and Mega Ampere Spherical Tokamak (MAST) in UK, active ST research has been
conducted worldwide. More than sixteen ST research facilities operating during this
period have achieved remarkable advances in all of fusion science areas, involving
fundamental fusion energy science as well as innovation. These results suggest exciting
future prospects for ST research both near term and longer term. The present paper
reviews the scientific progress made by the worldwide ST research community during
this new mega-ampere-ST era.
__________________________________________________
Submitted to: Physics of Plasmas (January, 2014)
__________________________________________________
Download PPPL-5030 (pdf 21 MB 150 pp)
__________________________________________________