Runaway Electron Behaviors In EAST Disruptions

Disruptions and runaway electrons(REs)produced during disruptions pose serious threat to tokamak wall,which including heat loads and electro-magnetic loads are both intolerable for large-scale tokamak.Hence,further understanding of disruption and REs are essential for disruption mitigation/avoidance,and are issues of the most attention in future tokamak research such as ITER.In this dissertation,EAST disruption database is established and covers key parameters to describe disruption,magnetic energy dissipation during current quench phase is analyzed based on this disruption database.Generation of REs during disruption are further studied with different discharge condition,RE loss caused by MHD instabilities and kinetic instabilities are analyzed to figure out underlying physic mechanism.Setup of disruption database in EAST is the basic,which provides a large number of plasma parameters describing the pre-disruptive plasma and disruptions over 2000 discharges with ITER-like tungsten divertor,also support further disruptive REs research.Based on this disruption database,plasma magnetic energy dissipation during current quench phase and current quench time is systematically studied.Besides,REs is also an important channel of magnetic energy dissipation.This dissertation detailly introduces experimental observations of RE behaviors in EAST post-disruption plasma.Moreover,a 0-D RE generation model is developed based on the RE generation mechanism,including primary(Dreicer mechanism and hot-tail mechanism)and secondary(Avalanche)mechanism,other RE seed sources are especially taken into consideration.This model,on the one hand,explains inconsistence between observation result and theory prediction;on the other hand,confirms that it is an RE-seed-dominated regime in EAST disruptions.In this model,other RE source can be suprathermal electrons driven by LHWs or REs generated during flattop phase in EAST low-density ohmic discharges.Besides,in MGI(massive gases injection)triggering disruptions,REs generation influenced by three types gases are also studied in this dissertation.Finally,RE loss event in EAST during disruption are also researched because it is the interplay between RE generation and loss mechanism that actually determines whether an RE plateau can be formed.During RE plateau phase,large-and small-scale instabilities are observed causing RE prompt losses,in which both can be divided into two components:(m,n)=(1,0)and(m,n)=(3,1).Large-scale instabilities are urther identified as external kink mode,small-scale instabilities are whereas resolved with kinetic instabilities as negative loop voltage modified RE distribution function.Moreover,RE loss event is correlated with magnetic perturbation amplitude.At the onset of current quench phase,RE losses event are also observed correlated with frequency of electrostatic fluctuations.In argon injection cases,frequencies of fluctuations vary from 30-40 kHz,however,in neon injection cases,there are two separated modes of frequency10-20 kHz and 30-40 kHz.Note that no fluctuations can be observed with helium injection,consistent with RE generations in these cases,suggesting that electrostatic fluctuations are driven by REs.The spatial component is identified as(m,n)=(1,0)by SVD method.