Quiescent H-mode operation using torque from non-axisymmetric, non-resonant magnetic fields

摘要

Quiescent H-mode (QH-mode) sustained by magnetic torque from non-axisymmetric magnetic fields is a promising operating mode for future burning plasmas including ITER. Using magnetic torque from n = 3 fields to replace counter-I_p torque from neutral beam injection, we have achieved long duration, counter-rotating QH-mode operation with neutral beam injection (NBI) torque ranging continuously from counter-I_p up to co-I_p values of about 1 N m. This co-I_p torque is about 3 times the scaled torque that ITER will have. This range also includes operation at zero net NBI torque, applicable to rf wave heated plasmas. These n = 3 fields have been created using coils either inside or, most recently, outside the toroidal coils. Experiments utilized an ITER-relevant lower single-null plasma shape and were done with ITER-relevant values ν_(ped) ～0.08,β_T~(ped) ～ 1 % and β_N = 2. Discharges have confinement quality H_(98y2) = 1.3, exceeding the value required for ITER. Initial work with low 995 = 3.4 QH-mode plasmas transiently reached fusion gain values of G = β_N H(89/q_(95)~2) = 0.4, which is the desired value for ITER; the limits on G have not yet been established. This paper also includes the most recent results on QH-mode plasmas run without n = 3 fields and with co-I_p NBI; these shots exhibit co-I_p plasma rotation and require NBI torque ≥2 N m. The QH-mode work to date has made significant contact with theory. The importance of edge rotational shear is consistent with peeling-ballooning mode theory. We have seen qualitative and quantitative agreement with the predicted torque from neoclassical toroidal viscosity.