The penetration depths of different impurity pellets, such as carbon and neon, injected
into different thermonuclear devices were reproduced by means of a single numerical
code with the same set of assumptions, only the atom physical data being changed.
All major characteristics of the ablation process were calculated: the spatial variation of
the ablation rate, the depositon of ablated particles at a succession of magnetic
flux surfaces, the expansion of deposited particles in the directions both parallel
and perpendicular to the magnetic field lines, and the temporal and spatial variations
of the radiant power emitted by the expanding impurity cloud. The calculations were
done by means of a time dependent quasi-three-dimensional code consisting of three
modules accounting for the B⊥ and B|| expansions of the cloud and the
traversing motion of the pellet, operated interactively and, when needed, iteratively. The
radiation characteristics were computed by a collisional-radiative loss model, developed
for low temperature light impurities, without the usual equilibrium assumptions. With
some modifications, the code is adaptable to predictive pre-disruptive `killer pellet'
scenario calculations for future large scale machines, such as ITER.
The current-voltage characteristics of a biased electrode (flush mounted probe) and the potential
and current distributions are analysed for three basic mechanisms of conductivity across the magnetic
field (viscosity, inertia, ion-neutral collisions) in a fully ionized plasma for probe sizes larger than the
ion gyro-radius. The analysis was performed both analytically (for small probe potentials) and numerically. It is
shown that the slope of the transitional part of the I-V characteristics is approximately the same for all types
of conductivity, provided the probe current is normalized to the ion sonic flow to the return current collecting
area, while the probe voltage is measured in electron temperature units. The characteristic scale of the plasma perturbed
region along the magnetic field is of the order of λmfp(mi/me)1/2 for all three mechanisms considered. The transverse scale is essentially determined by the type of transverse conductivity.
A problem of a flush-mounted probe in a fully ionized magnetized plasma (such as SOL plasma) is treated analytically and numerically for arbitrary probe size. The model describes the structure of electric field and particle fluxes, as well as the transport processes, in a plasma zone disturbed by the probe. The I-V characteristics and the structure of return current to the electrode are derived on this basis.
The I-V characteristics in a hlly ionized plasma are calculated for the probes larger than the ion gyroradius. The shape of the characteristics is crucially effected by the transverse conductivity caused by the perpendicular ion viscosity.
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