Speaker
Description
See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1027.pdf
First impurity seeding experiments with N and Ne injection in the new SAS (Small Angle Slot) divertor at DIII-D show the simultaneous achievement of divertor detachment, stable discharge behavior and unchanged (N) or even improved pedestal performance (Ne). N seeding in the SAS divertor leads to the simultaneous observation of detachment on all the boundary diagnostics including LPs, DTS, ASDEX Gauges, EUV spectrometer with a 20% increase in the pedestal density fluctuations. In matched N discharges with different strike point locations, the detachment onset requires different N levels, highlighting an important dependence of detachment on strike point location. Such dependence is also confirmed by the different N content reaching the core as indicated by both CER and SPREAD core measurements. SOLPS simulations investigating the role of impurity trapping in the divertor suggest that impurities may be more manageable when puffed into the SAS. The comparison of matched N and Ne cases indicates that N seeding does not change the pedestal profiles, while Ne leads to higher pedestal pressure gradients. ELITE simulations show that Ne injection is associated with improved ballooning branch stability due to increased diamagnetic ion frequency by impurity stabilization of ITG turbulence as indicated by DBS measurements. Evidence of reduced ion transport in the core are also supported by TRANSP analysis and linear GYRO simulations which indicate a reduction of the growth rate of the low-k instabilities at the radius where the ion transport drops significantly. These experiments might represent a possible path to improve pedestal ballooning stability with improved ion core transport.
Work supported under USDOE Cooperative Agreements DE-FC02-04ER54698 and DE-AC05-00OR22725.
