Beam Probe Imaging of Electron Density in the Chaotic Region of CHS

A neutral lithium beam probe (LiBP) for the Compact Helical System (CHS) has been extended to a two-dimensional imaging diagnostic (2-D-LiBP). Two-dimensional image of the plasma structure in the edge and separatrix region of the l = 2 helical device is obtained by changing the beam injection angle mechanically, shot-to-shot. The 2-D image has shown the asymmetric plasma structure in the edge separatrix region, suggesting that 2-D diagnostic is essential in the chaotic magnetic field region where magnetic surfaces are not defined by a flux function.