Determination of pitch angles of magnetic field lines in tokamak with obliquely injected helium beam

Pitch angles of magnetic field lines or q-profile in high density tokamaks can be determined by the method proposed here. Blobs of monoenergetic helium beam with different velocities are injected into the tokomak obliquely to the toroidal direction on a poloidal plane x. Produced He(+) ions move nearly along the magnetic field lines, and their front emitting a HeII line crosses a different sight plane and forms a curve on it. Optically measured shift of the curve from x leads to the distribution of pitch angle after correction of perpendicular drift motion of He(+) ions using the velocity dependence of the drift.