Density Limit is Found Related to Impurity Accumulation and Neutral Particles’ Recycling
count: [2016-05-24]

Recently, researchers from ASIPP studied the physics related to the density limits and high density operation on EAST tokamak and found that the density limit phenomenon is closely related to the impurity accumulation and recycling of neutral particles in the divertor region.   

Plasma density is one of the most important parameters in the fusion plasma research. High density operation can create beneficial conditions for the ignition, and it should be the basic requirement of the fusion plant in the future.

In EAST, density limit discharge could be achieved generally by strong or just moderate fueling rate. Based on the analysis of L-mode and H-mode density limit discharges on EAST, researchers found that the Ohmic and L-mode density limit scaling on EAST is basically in line with Greenwald scaling. However, the H-mode density limit is about 0.8-0.9nGW. It seems that the density limit has a positive correlation with heating power when it is low, while this relationship becomes inconspicuous when the heating power increases to a higher level.

Density limit is greatly related to the edge cooling of plasma, in which impurities and neutral particles recycling play a very important role. This has been confirmed through statistical analysis of the relation of ne/nGW with Zeff and impurities intensities (OII, W and CIII). 

Besides, most high density discharges were achieved by SMBI fueling, indicating that SMBI is a better fueling method for high density operation.  

By careful control of impurities and recycling, high density up to 0.93nGW stable H-mode operation was achieved by 1.7 MW LHW and 1.9 MW ICRF with SMBI fueling. It provides a good reference for the long-pulse high density plasma research for EAST and ITER. (ZHENG Xingwei reports)

 

 The density operation space of four recent operation campaigns in EAST tokamak. The operation space has been extended due to application of advanced wall conditioning methods and improvement of auxiliary heating power.