H. Wurz et al., NUMERICAL MODELING AND EXPERIMENTAL SIMULATION OF VAPOR SHIELD FORMATION AND DIVERTOR MATERIAL EROSION FOR ITER TYPICAL PLASMA DISRUPTIONS, Journal of nuclear materials, 215, 1994, pp. 1349-1352
The high divertor heat load during a tokamak plasma disruption results
in sudden evaporation of a thin layer of divertor plate material, whi
ch acts as vapor shield and protects the target from further excessive
evaporation. Formation and effectiveness of the vapor shield are theo
retically modeled and experimentally investigated at the 2MK-200 facil
ity under conditions simulating the thermal quench phase of ITER tokam
ak plasma disruptions. In the optical wavelength range C II, C III, C
IV emission lines for graphite, Cu I, Cu II lines for copper and conti
nuum radiation for tungsten samples are observed in the target plasma.
The plasma expands along the magnetic field lines with velocities of
(4 +/- 1) X 10(6) cm/s for graphite and 10(5) cm/s for copper. Modelin
g was done with a radiation hydrodynamics code in one-dimensional plan
ar geometry. The multifrequency radiation transport is treated in flux
limited diffusion and in forward reverse transport approximation. In
these first modeling studies the overall shielding efficiency for carb
on and tungsten defined as ratio of the incident energy and the vapori
zation energy for power densities of 10 MW/cm(2) exceeds a factor of 3
0. The vapor shield is established within 2 mu s, the power fraction t
o the target after 10 mu s is below 3% and reaches in the stationary s
tate after about 20 mu s a value of around 1.5%.