Characterization of the wall recycling properties and bulk particule life time from cx measurements in Tore Supra
One of the major goals of Tore Supra is to study very long pulses for which the density control is of crucial importance. For quasi steady state conditions (sources and sinks are equal), three parameters are sufficient to describe the total particle balance: - the number of particles present in the wall and available to refuel the plasma (N(w)), - the equilibrium plasma density n(e) and - the particle confinement time tau(p). In order to obtain quantitative information on the source and sink capabilities of the graphite wall, the evolution of the plasma isotopic ratio is analysed, complemented by the shot to shot gas balance. From this set of data is deduced the number N(W), which is shown to be much smaller than the total particle content of the wall. For ohmic discharges, the equilibrium plasma density, n(e), is very sensitive to this parameter. The last parameter, tau(p), is deduced from pellet injection experiments. When deuterium pellets are injected into a hydrogen plasma, ro(p) decreases in a time much shorter than the charge-exchange diagnostic time resolution (a few milliseconds), and then recovers its original equilibrium value on a longer time scale (tau(c), if fitted with an exponential law). If the recycling conditions are such that the global evolution time of the density is much larger than tau(c), the latter appears to be a simple combination of the hydrogen and deuterium lifetimes (weighted by the wall isotopic ratio) and gives a direct measurement of the deuterium lifetime, if the content of the wall is mainly hydrogen. In the opposite case (the density decreases sharply after the pellet injection), it must be assumed that the particle confinement time tau(p) is identical for the two isotopes. The knowledge of the apparent particle confinement time then makes it possible to determine the value of tau(p) from the global recycling coefficient during this transient phase.
Bibliographic Reference: Paper presented: 18th European Conference of the EPS-Plasma Physics Division, Berlin (DE), June 3-7, 1991
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Record Number: 199110387 / Last updated on: 1994-12-02
Original language: en
Available languages: en