(TH/P2-10) MHD Equilibrium and Pressure Driven Instability in L=1 Heliotron Plasmas

**Abstract.** Free boundary MHD equilibrium properties of Heliotron J are
investigated by VMEC, HINT and PIES codes, and ideal MHD stability
properties are studied by the Mercier criterion, the ballooning mode
equation and CAS3D global stability code. It is shown by the equilibrium
calculation that the change of plasma boundary shape is substantial in a low
shear helical system even if the beta is relatively low. Comparison between
PIES results and HINT results is shown. From the stability analysis, good
correlation is found between local and global analyses for the 3D or helical
ballooning mode whose mode structure shows strong poloidal and toroidal mode
couplings. In the 3D ballooning mode, the eigenmode is localized in a flux
tube. It is also found that the positive shear of the rotational transform
is favorable for the 3D ballooning mode stability in a low shear helical
system. The role of the magnetic shear on the 3D ballooning mode in a low
shear helical system is clarified.

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*IAEA 2003*