Sawtooth behavior of EAST plasma under ICRF heating

BackgroundSawtooth oscillations are macroscopic instabilities in plasma. To better control the sawtooth oscillation in an advanced experimental superconducting tokamak (EAST) device, it is necessary to develop sawtooth controlling methods that help improve the confined performance of plasma in the EAST device.PurposeThis study aims to analyze sawtooth behavior under the on-axis heating by ion cyclotron resonance frequency (ICRF) wave in the EAST device.MethodsFirst of all, the soft X-ray integrated signal intensity data was used to analyze the sawtooth period and amplitude. The radius of q=1 surface and the plasma pressure gradient at q=1 surface were calculated using a soft X-ray intensity profile. Then the neutron yield flux was obtained from the neutron yield flux diagnostic data. Finally, the equilibrium reconstruction results of the equilibrium fitting algorithm (EFIT) were combined with polarimeter-interferometer (POINT) diagnostic data to investigate the relationship between the variation of ICRF and plasma current density.ResultsExperimental results show that the sawtooth period is positively correlated with the ICRF power, and the variation in sawtooth period is roughly same as that in sawtooth amplitude and plasma pressure gradient at q=1 surface. The ICRF power needs to exceed 0.8 MW to change the radius of q=1 surface. The sawtooth period and q=1 surface with ICRF power change are more sensitive under solely ICRF heating than under ICRF+lower hybrid wave (LHW)+electron cyclotron resonance heating (ECRH).ConclusionsSawtooth behavior of EAST plasma is affected by the fast ions produced by ICRF and the radius change of q=1 surface.