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Determination of Pitch Angles of Magnetic Field Lines in Tokamak with Obliquely Injected Helium Beam

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