MODIFICATION OF TURBULENT TRANSPORT BY ORBIT AVERAGING

The effect on plasma turbulence of orbit averaging by thermal ions is considered. This effect can reduce the ion response, modifying the mode growth rate, which in turn changes the turbulent transport. For the trapped electron mode, this mechanism provides a potential explanation of the observed more favourable scaling of chi(i) with T(i) in supershots than in L-modes. Also, for this mode and for the ion temperature gradient mode, the effect modifies earlier transport expressions by a 'neoclassical factor', making the scalings of transport coefficients with magnetic field and current nearer those found experimentally.