Experimental And Numerical Simulation Study Of Ion Cyclotron Emission Driven By Energetic Ions

Effective confinement of energetic ions,especially fusion product D? ions,is necessary for achieving self-sustained nuclear burning.Energetic ions are the key to maintain the self-sustained fusion reaction,but a large number of escaping energetic ions will cause serious damage to the first wall of the device.Therefore,in the existing Tokamak,experimental researches on the distribution,confinement and interaction of energetic ions with plasma are important.The nature of ion cyclotron emission(ICE)is electromagnetic waves excited by high-energy ions.This electromagnetic radiation carries a lot of information of energetic ions.With a comprehensive understanding of the relationship between ICE and energetic ions,control the energetic ions confinement and transport would be possible.On the EAST Tokamak,taking into account the physical requirements,experimental conditions and engineering constraints of the device,and accompany with the existing diagnostic systems and neutral beam injection heating,a specific B-dot probe based diagnostic system had been designed to detect ICE intensity and spectrum distribution.A big rectangular magnetic coil(20cm×10cm)is designed to be the high-frequency B-dot probe which is a significant component of the diagnostic system,and the plane of the magnetic coil is perpendicular to the toroidal magnetic field.A spectrum analyzer is used to analyze the spectral distribution of ICE,and a 100 kHz/s acquisition card is used to analyze the ICE intensity evolution.The diagnostic system was designed and installed on the EAST in the fall of 2017.First results from experiments was obtained in the spring of 2018.Various types of ICE were observed from experiments with sub-Alfvenic deuterium beam ions injected into deuterium in EAST.Experimental investigations have found that in either L or H modes,both edge and core ICE had been detected.In the L-mode plasma discharge,it is found that the characteristics of ICE are closely related to the injection angle and position of the neutral source beams.The variation trend of core ICE intensity is the same with the neutron radiation,it means that fusion ions has taken a position on core ICE.In H-mode discharges,it is found that the drop of ICE signals accompanies with the edge localized mode which could changing the plasma density and distribution of energetic ions in the low-field side edge region.In the H-mode discharges without edge localized mode,we found that the frequencies of core ICE are consistent with the ion cyclotron resonance frequencies of the hydrogen,deuterium(?D=2?H)and tritium ion which is from fusion reaction.In addition,some other important experimental results are described:1.the ICE is successfully measured when the plasma disruption,there was no neutral beam or ion cyclotron resonance heating during the entire discharge,and the ICE frequency is consistent with the resonance frequency of the domain plasma deuterium ions;2.after neutral beam injection turning off,only with the ohmic and the 4.6 GHz low hybrid wave,edge ICE driven by energetic deuterium ions still exist for more than 1 s;3.the low hybrid wave current drive and heating does influence the ICE intensity and spectrum.Bursts of ion cyclotron emission(ICE),with spectral peaks corresponding to the hydrogen cyclotron frequencies in the plasma core,are detected from helium plasmas heated by sub-Alfvenic beam-injected hydrogen ions in the ASDEX Upgrade tokamak.Based on the fast ion distribution function obtained from TRANSP and its fast ion NUBEAM code,together with a linear analytical theory of the magnetoacoustics cyclotron instability(MCI),we can calculate the growth rates of MCI.In our theoretical and experimental studies,we found that the excitation mechanism of core ICE driven by sub-Alfvenic beam ions in ASDEX Upgrade is MCI as the time evolution of MCI growth rates are broadly consistent with ICE amplitudes:(1)ICE amplitude is stronger during 71 keV NBI-8(1.5 MW)working even though the power of it is weaker compared to 52 keV NBI-3(1.8 MW);(2)ICE signal falls off extremely rapidly after NBI turn-off;(3)ICE signal with fundamental frequency is much stronger than that with second harmonic.From Numerical Simulation,it is clear that the MCI is very sensitive to beam-injected ion energy(hence,ion speed value)and is suppressed by the slowing down of the dominant beam-injected ion velocity.