Abstract: | The spectrum effect on the penetration of resonant magnetic perturbation (RMP) is studied with
upgraded in-vessel RMP coils on J-TEXT. The poloidal spectrum of the RMP field, especially
the amplitudes of 2/1 and 3/1 components, can be varied by the phase difference between the
upper and lower coil rows, Δϕ=ϕtop−ϕbottom, where ϕtop and ϕbottom are the toroidal phases of
the n = 1 field of each coil row. The type of RMP penetration is found to be related to Δϕ,
including the RMP penetration of either 2/1 or 3/1 RMP and the successive penetrations of 3/1
RMP followed by the 2/1 RMP. For cases with penetration of only one RMP component, the
penetration thresholds measured by the corresponding resonant component are close for various
Δf. However, the 2/1 RMP penetration threshold is significantly reduced if the 3/1 locked
island is formed in advance. The changes in the rotation profile due to 3/1 locked island
formation could partially contribute to the reduction of the 2/1 thresholds. |