Study Of 3D Structure On Divertor Heat And Particle Fluxes Induced By Edge Topology Change

The high heat and particle fluxes on divertor targets is one of the critical issues for long-pulse steady-state high-power operations on the tokamak devices.On the one hand,EAST upgrades the upper divertor from graphite to tungsten(W)to enhance the heat load capability,and employs the advanced divertor configuration to lower the vertical heat flux;On the other hand,EAST could use the rediative divertor to exhaust the plasma energy by high radiation or use the additional perturbation fields to reduce the heat load on the divertor targets.The lower hybrid wave(LHW)or the resonant magnetic perturbation(RMP)induced magnetic topology change could generate extra magnetic flux tubes near the X-point,which directly connects to the divertor targets and lead to secondary or even multiple strike regions near the orginal strike point,thus reducing the particle and heat fluxes on the original strike point as well as the peak heat flux on the whole divertor targets.This thesis is based on the EAST device and mainly focuses on the three dimensional(3D)effect of magnetic perturbations induced by lower hybrid wave(LHW)on the particle and heat flux distribution on divertor targets,and the ffect of impurity seeding and coupling with magnetic perturbations on 3D particle flux distribution and tungsten sourcing in EAST.The details are as follows:(1)3D divertor particle flux footprints induced by the LHW have been systematically investigated in the EAST superconducting tokamak.The striated particle flux(SPF)peaks away from the strike point(SP)closely fit the pitch of the edge magnetic field line for different safety factors q95,as predicted by a field line tracing code taking into account the helical current filaments(HCFs)in the scrape-off-layer(SOL).Besides L mode discharges,the LHW-induced particle and heat flux striations are also present in the H-mode plasmas,reducing the peak heat flux and erosion at the main strike point,thus facilitating long-pulse operation with a new steady-state H-mode over 100 seconds being recently achieved in EAST.(2)The 3D particle flux distribution could be influenced by the LHW power,plasma density and the direction of the magnetic field.The 3D SPF structure is observed with a LHW power threshold(PLHW?0.9 MW).The ratio of the particle fluxes between SPF and outer strike point(OSP),i.e.,?ion,SHF/?ion,OSP,increases with the LHW power.Upon transition to divertor detachment,the particle flux at the main OSP decreases,as expected,however,the particle flux at SPF continues increasing,in contrast to the RMP-induced striations that vanish with increasing divertor density.In addition,we also find that the in-out asymmetry of the 3D particle flux footprint pattern exhibits a clear dependence on the toroidal field direction(B×(?)B? and BxVBT).(3)Impurity seeding has been investigated as an active means to control heat and particle fluxes and erosion at the W divertor on EAST in the presence of 3D perturbation fields generated by LHW or resonant magnetic perturbation(RMP).Experiments using neon impurity seeding coupled with LHW show a promising capability in 3D particle and heat flux control on EAST.It is found that the neon seeding reduces the heat and particle fluxes at OSP and affects the 3D SPF in the far SOL,induced by LHW.(4)Neon seeding also affects the 3D SPF induced by RMP.With an appropriate level of neon seeding or lithium aerosol injection,the W sputtering can be significantly reduced,resulting from the reduction of Te near divertor targets,thus benefiting long-pulse steady-state operations,while trace neon seeding may lead to enhanced W sourcing by neon when Te is not sufficiently lowed.These works shown above not only provide the evidence(including the modeling)of 3D divertor footprint induced by lower hybrid waves and the characteristics of them on heat and particle flux distribution under different plasma parameters,but also couple the edge magnetic perturbations with impurity seeding to provide a promising a method on 3D divertor heat and particle distributions.This thesis is significant for the active control of heat and particle fluxes in future fusion devices.