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Title: Vapor shielding models and the energy absorbed by divertor targets during transient events

The erosion of divertor targets caused by high heat fluxes during transients is a serious threat to ITER operation, as it is going to be the main factor determining the divertor lifetime. Under the influence of extreme heat fluxes, the surface temperature of plasma facing components can reach some certain threshold, leading to an onset of intense material evaporation. The latter results in formation of cold dense vapor and secondary plasma cloud. This layer effectively absorbs the energy of the incident plasma flow, turning it into its own kinetic and internal energy and radiating it. This so called vapor shielding is a phenomenon that may help mitigating the erosion during transient events. In particular, the vapor shielding results in saturation of energy (per unit surface area) accumulated by the target during single pulse of heat load at some level E max. Matching this value is one of the possible tests to verify complicated numerical codes, developed to calculate the erosion rate during abnormal events in tokamaks. The study presents three very different models of vapor shielding, demonstrating that E max depends strongly on the heat pulse duration, thermodynamic properties, and evaporation energy of the irradiated target material. While its dependencemore » on the other shielding details such as radiation capabilities of material and dynamics of the vapor cloud is logarithmically weak. The reason for this is a strong (exponential) dependence of the target material evaporation rate, and therefore the “strength” of vapor shield on the target surface temperature. As a result, the influence of the vapor shielding phenomena details, such as radiation transport in the vapor cloud and evaporated material dynamics, on the E max is virtually completely masked by the strong dependence of the evaporation rate on the target surface temperature. However, the very same details define the amount of evaporated particles, needed to provide an effective shielding to the target, and, therefore, strongly influence resulting erosion rate. Finally and thus, E max cannot be used for validation of shielding models and codes, aimed at the target material erosion calculations.« less
Authors:
 [1] ; ORCiD logo [2] ;  [1] ;  [2] ;  [2] ;  [3]
  1. Budker Inst. of Nuclear Physics, Novosibirsk (Russian Federation)
  2. National Research Nuclear Univ. MEPhI, Moscow (Russian Federation)
  3. National Research Nuclear Univ. MEPhI, Moscow (Russian Federation); Univ. of California, San Diego, CA (United States)
Publication Date:
Grant/Contract Number:
FG02-04ER54739; 15-32-20669; 14.Y26.31.0008
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 2; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of California, San Diego, CA (United States); Budker Inst. of Nuclear Physics, Novosibirsk (Russian Federation); National Research Nuclear Univ. MEPhI, Moscow (Russian Federation)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); Russian Foundation for Basic Research (RFBR); Russian Ministry of Education and Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma flows; plasma confinement; plasma facing components; dimensional analysis; tokamaks; transition metals; chemical bonding; plasma dynamics; thermodynamic properties; thermodynamic states and processes
OSTI Identifier:
1469154
Alternate Identifier(s):
OSTI ID: 1236524

Skovorodin, D. I., Pshenov, A. A., Arakcheev, A. S., Eksaeva, E. A., Marenkov, E. D., and Krasheninnikov, S. I.. Vapor shielding models and the energy absorbed by divertor targets during transient events. United States: N. p., Web. doi:10.1063/1.4939537.
Skovorodin, D. I., Pshenov, A. A., Arakcheev, A. S., Eksaeva, E. A., Marenkov, E. D., & Krasheninnikov, S. I.. Vapor shielding models and the energy absorbed by divertor targets during transient events. United States. doi:10.1063/1.4939537.
Skovorodin, D. I., Pshenov, A. A., Arakcheev, A. S., Eksaeva, E. A., Marenkov, E. D., and Krasheninnikov, S. I.. 2016. "Vapor shielding models and the energy absorbed by divertor targets during transient events". United States. doi:10.1063/1.4939537. https://www.osti.gov/servlets/purl/1469154.
@article{osti_1469154,
title = {Vapor shielding models and the energy absorbed by divertor targets during transient events},
author = {Skovorodin, D. I. and Pshenov, A. A. and Arakcheev, A. S. and Eksaeva, E. A. and Marenkov, E. D. and Krasheninnikov, S. I.},
abstractNote = {The erosion of divertor targets caused by high heat fluxes during transients is a serious threat to ITER operation, as it is going to be the main factor determining the divertor lifetime. Under the influence of extreme heat fluxes, the surface temperature of plasma facing components can reach some certain threshold, leading to an onset of intense material evaporation. The latter results in formation of cold dense vapor and secondary plasma cloud. This layer effectively absorbs the energy of the incident plasma flow, turning it into its own kinetic and internal energy and radiating it. This so called vapor shielding is a phenomenon that may help mitigating the erosion during transient events. In particular, the vapor shielding results in saturation of energy (per unit surface area) accumulated by the target during single pulse of heat load at some level Emax. Matching this value is one of the possible tests to verify complicated numerical codes, developed to calculate the erosion rate during abnormal events in tokamaks. The study presents three very different models of vapor shielding, demonstrating that Emax depends strongly on the heat pulse duration, thermodynamic properties, and evaporation energy of the irradiated target material. While its dependence on the other shielding details such as radiation capabilities of material and dynamics of the vapor cloud is logarithmically weak. The reason for this is a strong (exponential) dependence of the target material evaporation rate, and therefore the “strength” of vapor shield on the target surface temperature. As a result, the influence of the vapor shielding phenomena details, such as radiation transport in the vapor cloud and evaporated material dynamics, on the Emax is virtually completely masked by the strong dependence of the evaporation rate on the target surface temperature. However, the very same details define the amount of evaporated particles, needed to provide an effective shielding to the target, and, therefore, strongly influence resulting erosion rate. Finally and thus, Emax cannot be used for validation of shielding models and codes, aimed at the target material erosion calculations.},
doi = {10.1063/1.4939537},
journal = {Physics of Plasmas},
number = 2,
volume = 23,
place = {United States},
year = {2016},
month = {2}
}