Sherwood 2015

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On the vapor shielding of divertor target

Author: Sergei Krasheninnikov
Requested Type: Poster Only
Submitted: 2015-01-09 14:16:35


Contact Info:
University California San Diego
9500 Gilman Dr., Engineering B
La Jolla, CA   92093-0
United States

Abstract Text:
Experiments with plasma guns followed by rather comprehensive numerical simulations [1-3] have demonstrated the impact of shielding effects as a response of the wall material (both CFC and Tungsten) on the incident plasma heat flux, which is as high in magnitude as the heat flux caused by giant ELMs and disruptions in ITER. In particular, the vapor plasma shielding results in the saturation of the energy (per unit surface area) accumulated by the wall at some level, Emax, even though the total energy (per unit surface area) delivered by plasma can be significantly larger than Emax (see Fig. 6 in Ref. 1). However, what is interesting is that Emax appears to be practically the same for both CFC and Tungsten [1, 2], even though the radiation capabilities of CFC and Tungsten are very much different [4]. To shade the light on these curious results we consider three very different models of the shielding effects and estimate Emax. From all these models we found that Emax obeys the same function, which includes the pulse time of the plasma gun, the heat conduction coefficient and heat diffusivity of the wall material, and the evaporation energy. The dependence of Emax on all other parameters of the models (e.g. specific heat flux on unshielded target, radiation properties and stopping power of evaporated atoms, etc.) is logarithmically weak. For both, Tungsten at CFC, we find that our estimate of Emax is very close to the available experimental data and, which is in agreement with experiment, and are virtually the same. It might be not surprising, since surface temperature, Ts, is much smaller than the evaporation energy. As a result, the details of the shielding phenomena are virtually completely masked by a strong dependence of the evaporation rate on Ts. However, contrarily to Emax, the total number of ablated particles (per unit surface area), Nmax, can be very sensitive to the details of the shielding model.
[1] Safronov V M, et al 2009 J. Nucl. Mater. 386-388 744; [


March 16-18, 2015
The Courant Institute, New York University