Review of Scientific Instruments
The assumptions of the evaporation model for low-Z pellets interacting with magnetic fusion plasmas developed by Parks are tested. These assumptions are that the vapor density profile in the region adjacent to the pellet surface falls off with radial distance as r-α , where 5 <α<6, and that the ionization time for the transition between charge states זf (i.e., for r < ~3 sonic radii). The first assumption is tested by solving a two-parameter eigenvalue problem for the evaporation cloud in the region interior to the sonic radius; the results are found to be consistent with the low-Z evaporation model. The second assumption, that זzi «זf, is tested at the sonic radius using the results from atomic physics and the low-Z evaporation model. It is found that indeed זzi «זf for plasmas with parameters close to thermonuclear conditions (e.g. CIT), but not for those of smaller Tokamaks such as TEXT. The results of pellet penetration calculations for the conditions of the carbon-pellet injection experiments into TEXT and low-density TFTR plasmas are presented that show better agreement with experiment if the shielding fraction is calculated at each step of the pellet penetration calculation, the effect of ionization is ignored, and if the effect of possible uncertainties in the background plasma parameters is included.
Original Publication Citation
Vahala, L.L., Elcashlan, A.G., Gerdin, G.A., & Parks, P.B. (1990). Application of the results of carbon pellet modeling to the problem of plasma penetration. Review of Scientific Instruments, 61(10), 3140-3142. doi: 10.1063/1.1141707
Vahala, L. L.; El Cashlan, A. G.; Gerdin, G. A.; and Parks, P. B., "Application of the Results of Carbon Pellet Modeling to The Problem of Plasma Penetration" (1990). Electrical & Computer Engineering Faculty Publications. 43.