Spatial structure of particle-orbit loss regions in l=2 helical systems

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Abstract
Particle orbits and loss regions in both configuration and velocity spaces are studied on the basis of adiabatic invariants and guiding‐center drift equations. The boundary of the loss region in the pitch angle major radius plane (χ0‐ρ) is determined from the condition of whether the drift surfaces for helically trapped and transition particles hit the limiter or not. Two typical loss boundaries on the χ0‐ρ plane are obtained. One determines the boundary of absolute confinement where no particles are lost. The other gives the boundary of the confined region of deeply trapped particles with v∥=0. An analytical form describing the latter boundary is also derived. Effects of ripple modulation and electrostatic potential on these loss boundaries are discussed for the improvement of particle confinement.