Plasma Zonal Flows

 

Zonal flows are found in both low and high cofinement modes

 

 

Two branches are observed:

 

- mean-zero-frequency zonal flows with m=n=0

- finite-frequency modes with m=n=0, or geodesic acoustic modes (GAM)

 

 

The first experimental evidence of the finite-frequency zonal flows in toroidal plasma is presented in:

 

Shats M. G., Solomon W. M. Experimental evidence of self-regulation of fluctuations by time-varying flows,
Physical Review Letters 88 (2002) 045001. [PDF]

 

 

 

Zonal flows play important roles in plasma . We found that they can be the key players in establishing the regions of improved plasma confinement, or transport barriers

:

 

H. Xia, M. G. Shats, H. Punzmann, Strong ExB shear flows in the transport-barrier region in H-mode plasma,

 

Physical Review Letters, 97, 255003 (2006) [PDF]

 

 

Punzmann H., Shats M.G., Formation and structure of transport barriers during confinement transitions in toroidal plasma,

 

Physical Review Letters, 93(12), 125003 (2004) [PDF]

 

 

 

 

Large turbulent structures greatly increase particle and energy loss from the plasma. However, this anomalous transport is substantially reduced when GAMs are developed. These zonal flows reduce transport driven by other structures via their phase randomization mechanism:

 

Shats M.G., Solomon W.M. and Xia H. Turbulent transport reduction and randomization of coherent fluctuations by zonal flows in toroidal plasma,
Physical Review Letters 90 (2003) 125002. [PDF]