Evolution of pellet clouds and cloud structures in magnetically confined plasmas
The subject of this study is the spatial and time evolution of initially low-temperature high-density particle clouds in magnetically confined hot plasmas, such as those produced by ablating cryogenic hydrogen pellets in fusion machines. Particular attention is given to: - such physical processes as heating of the cloud by the energy fluxes carried by incident plasma particles (classical flux-limited energy transport by thermal electrons along the magnetic field lines, anomalous heat conduction across them); - gasdynamic expansion with j x B-produced deceleration in the transverse direction; - finite-rate ionisation and recombination (collisional and radiative) processes, and - magnetic field convection and diffusion. The results show the existence of a distinct structure in the ablatant cloud surrounding an ablating pellet: a hollow temperature profile coupled to a peaked density profile in the plane normal to the magnetic field direction. The separation distance between the high- and low-temperature and density layers is typically the ionisation or confinement radius. The flutes developing preferentially at the cloud surface have, at a certain phase of their development, the same wavelength. The temperature and the density variations from the cloud interior to the cloud periphery may exceed two orders of magnitude. The lifetime of this structure is measured on hydrodynamic time scales.
Bibliographic Reference: Report: IPP 5/39 EN (1990) 35 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199110916 / Last updated on: 1994-12-02
Original language: en
Available languages: en