Drift orbit topology of fast ions in tokamaks

Graphical methods are developed by which the guiding centre orbit topology of fast ions in tokamaks is efficiently obtained and displayed. For constant energy we characterize the orbits by a new set of constant of motion variables (S,χ) describing the radial position and pitch angle of the orbits as they intersect with the stagnation surface. This surface is a generalization of the equatorial plane for non-top-bottom symmetric magnetic profiles. The orbit topology is obtained simply by studying the contours of the magnitude of the magnetic moment μ and canonical angular momentum p ϕ in the (S,χ) plane. The methods, suitable for routine analysis, can also be applied to evaluate the orbit topology in advanced tokamak scenarios where the presence of special orbit types (co-pinch orbits) causes first orbit loss of fusion products.