Velocity distribution of helium-atoms in front of the TEXTOR limiter
The velocity distribution of the atoms released from a tokamak limiter is very significant. On the one hand, it influences the penetration depth of the atoms into the plasma and therefore the particle confinement time. On the other hand, it may give information on the processes occurring at the limiter surface and in front of the limiter. In tokamak discharges in helium, the velocity distribution of helium atoms released from the limiter was determined by measuring in the radial direction the Doppler broadening of a singlet line (=6678 A), the Zeeman effect splitting of which was eliminated by a polarizer. The spectral line profile shows a central component, which is slightly shifted to the blue and which originates from desorbed helium atoms, and a high energy blue wing, which results from particles with energies up to 150eV. The high-energy helium particles are still present when discharges are operated in hydrogen with small amounts of helium added. Since under such conditions the resonant charge exchange of helium is strongly reduced, it is clear that the dominant part of the fast particles originates from reflected helium atoms.
Bibliographic Reference: Article: Journal of Nuclear Materials, Vol. 162-164 (1989), pp. 545-549
Record Number: 199010404 / Last updated on: 1994-12-01
Original language: en
Available languages: en