Assuming that energy confinement is dominated by the physics of fully ionised plasmas, it has been shown, theoretically, that the energy confinement time (tE) can be expressed in terms of the three dimensionless parameters r*(µ m0.5i T0.5/aBT ), n*(µ Ze f f naq/T2) and b(µ nT/B2T) [1, 2] where mi is the ion mass, T is the plasma temperature, n is the plasma density, R is the major radius and a the minor radius. BT and BP are the toroidal and poloidal magnetic fields.