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The properties of alpha particle confinement of m=2 stellarators have been studied as a function of the aspect ratio (in the range of R/a values from 3 to 12). A collisionless orbit calculation has been performed numerically for stellarator configurations obtained by winding the helicoidal currents on circular cross-section tori with constant pitch in toroidal coordinates. All the studied configurations exhibit pronounced separatrix-like features that also rotate with constant pitch in toroidal coordinates. The fraction of alpha particles contained within the last closed magnetic surface rapidly increases with the aspect ratio and is higher than 80% for R/a greater than 4. The escaping alpha particles cross the separatrix within narrow helical strips around the X-point path, when it is between the inboard and the upboard of the torus. The particle motion is also followed outside the closed magnetic surface. When the boundary (i.e. the surface where the helicoidal currents flow) is sufficiently far from the plasma, the escaping alpha particles are found to remain trapped in the X-point region.

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Authors: ALLADIO F, ENEA, Centro Ricerche Energia Frascati, Roma (IT);BATISTONI P, ENEA, Centro Ricerche Energia Frascati, Roma (IT);MANCUSO A, ENEA, Centro Ricerche Energia Frascati, Roma (IT)
Bibliographic Reference: Paper presented: IAEA Technological Committee Meeting on Alpha Particles in Fusion Research, Aspenäs, Göteborg (SE), June 10-14, 1991
Availability: Available from (1) as Paper EN 36368 ORA
Record Number: 199111202 / Last updated on: 1994-12-02
Original language: en
Available languages: en