The dependence of the Shafranov shift on magnetic field configuration, toroidicity and central rotational transform ι(0) in neutral beam heated plasma has been experimentally investigated in the Large Helical Device. The toroidicity of the plasma is controlled by the quadrupole field, while the central ι(0) is controlled by changing the distance of the current centre of the helical coil to the plasma. It is experimentally confirmed that both the lower toroidicity and the higher ι(0) contribute to the reduction of the Shafranov shift as predicted by the three-dimensional equilibrium code, VMEC.
Effect of helical coils on the magnetic field and the stability ofa compact toroidal plasma