skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Multi-scale modelling to relate beryllium surface temperature, deuterium concentration and erosion in fusion reactor environment

Abstract

Beryllium (Be) has been chosen as the plasma-facing material for the main wall of ITER, the next generation fusion reactor. Identifying the key parameters that determine Be erosion under reactor relevant conditions is vital to predict the ITER plasma-facing component lifetime and viability. To date, a certain prediction of Be erosion, focusing on the effect of two such parameters, surface temperature and D surface content, has not been achieved. In this paper, we develop the first multi-scale KMC-MD modeling approach for Be to provide a more accurate database for its erosion, as well as investigating parameters that affect erosion. First, we calculate the complex relationship between surface temperature and D concentration precisely by simulating the time evolution of the system using an object kinetic Monte Carlo (OKMC) technique. These simulations provide a D surface concentration profile for any surface temperature and incoming D energy. We then describe how this profile can be implemented as a starting configuration in molecular dynamics (MD) simulations. We finally use MD simulations to investigate the effect of temperature (300–800 K) and impact energy (10–200 eV) on the erosion of Be due to D plasma irradiations. The results reveal a strong dependency of the D surfacemore » content on temperature. Increasing the surface temperature leads to a lower D concentration at the surface, because of the tendency of D atoms to avoid being accommodated in a vacancy, and de-trapping from impurity sites diffuse fast toward bulk. At the next step, total and molecular Be erosion yields due to D irradiations are analyzed using MD simulations. The results show a strong dependency of erosion yields on surface temperature and incoming ion energy. The total Be erosion yield increases with temperature for impact energies up to 100 eV. However, increasing temperature and impact energy results in a lower fraction of Be atoms being sputtered as BeD molecules due to the lower D surface concentrations at higher temperatures. Finally, these findings correlate well with different experiments performed at JET and PISCES-B devices.« less

Authors:
 [1];  [2];  [3];  [1]
  1. Univ. of Helsinki (Finland)
  2. Technical Univ. of Madrid (Spain). Inst. of Nuclear Fusion
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Univ. of Helsinki (Finland); Technical Univ. of Madrid (Spain); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE; European Commission (EC)
OSTI Identifier:
1376422
Grant/Contract Number:
AC05-00OR22725; 633053
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physics. D, Applied Physics
Additional Journal Information:
Journal Volume: 50; Journal Issue: 20; Journal ID: ISSN 0022-3727
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 36 MATERIALS SCIENCE

Citation Formats

Safi, E., Valles, G., Lasa, A., and Nordlund, K.. Multi-scale modelling to relate beryllium surface temperature, deuterium concentration and erosion in fusion reactor environment. United States: N. p., 2017. Web. doi:10.1088/1361-6463/aa6967.
Safi, E., Valles, G., Lasa, A., & Nordlund, K.. Multi-scale modelling to relate beryllium surface temperature, deuterium concentration and erosion in fusion reactor environment. United States. doi:10.1088/1361-6463/aa6967.
Safi, E., Valles, G., Lasa, A., and Nordlund, K.. Mon . "Multi-scale modelling to relate beryllium surface temperature, deuterium concentration and erosion in fusion reactor environment". United States. doi:10.1088/1361-6463/aa6967. https://www.osti.gov/servlets/purl/1376422.
@article{osti_1376422,
title = {Multi-scale modelling to relate beryllium surface temperature, deuterium concentration and erosion in fusion reactor environment},
author = {Safi, E. and Valles, G. and Lasa, A. and Nordlund, K.},
abstractNote = {Beryllium (Be) has been chosen as the plasma-facing material for the main wall of ITER, the next generation fusion reactor. Identifying the key parameters that determine Be erosion under reactor relevant conditions is vital to predict the ITER plasma-facing component lifetime and viability. To date, a certain prediction of Be erosion, focusing on the effect of two such parameters, surface temperature and D surface content, has not been achieved. In this paper, we develop the first multi-scale KMC-MD modeling approach for Be to provide a more accurate database for its erosion, as well as investigating parameters that affect erosion. First, we calculate the complex relationship between surface temperature and D concentration precisely by simulating the time evolution of the system using an object kinetic Monte Carlo (OKMC) technique. These simulations provide a D surface concentration profile for any surface temperature and incoming D energy. We then describe how this profile can be implemented as a starting configuration in molecular dynamics (MD) simulations. We finally use MD simulations to investigate the effect of temperature (300–800 K) and impact energy (10–200 eV) on the erosion of Be due to D plasma irradiations. The results reveal a strong dependency of the D surface content on temperature. Increasing the surface temperature leads to a lower D concentration at the surface, because of the tendency of D atoms to avoid being accommodated in a vacancy, and de-trapping from impurity sites diffuse fast toward bulk. At the next step, total and molecular Be erosion yields due to D irradiations are analyzed using MD simulations. The results show a strong dependency of erosion yields on surface temperature and incoming ion energy. The total Be erosion yield increases with temperature for impact energies up to 100 eV. However, increasing temperature and impact energy results in a lower fraction of Be atoms being sputtered as BeD molecules due to the lower D surface concentrations at higher temperatures. Finally, these findings correlate well with different experiments performed at JET and PISCES-B devices.},
doi = {10.1088/1361-6463/aa6967},
journal = {Journal of Physics. D, Applied Physics},
number = 20,
volume = 50,
place = {United States},
year = {Mon Mar 27 00:00:00 EDT 2017},
month = {Mon Mar 27 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 3works
Citation information provided by
Web of Science

Save / Share:
  • Solid deuterium-tritium (D-T) fuel layers for inertial confinement fusion experiments were formed inside of a 2 mm diameter beryllium shell and were characterized using phase-contrast enhanced x-ray imaging. The solid D-T surface roughness is found to be 0.4 {micro}m for modes 7-128 at 1.5 K below the melting temperature. The layer roughness is found to increase with decreasing temperature, in agreement with previous visible light characterization studies. However, phase-contrast enhanced x-ray imaging provides a more robust surface roughness measurement than visible light methods. The new x-ray imaging results demonstrate clearly that the surface roughness decreases with time for solid D-Tmore » layers held at 1.5 K below the melting temperature.« less
  • Fusion neutronics experiments are performed on a full-coverage blanket with various configurations of a beryllium neutron multiplier. In the basic experimental system, a lithium carbonate enclosure contains a lithium oxide test zone and a deuterium-tritium neutron source to simulate a neutron spectrum in a fusion reactor. Five beryllium configurations are adopted to examine the effects of neutron multiplication and reflection by beryllium. The measurements are carried out along the central line in the test zone. Various measurement techniques are applied to obtain the tritium production rate distribution, which is one of the most important parameters for assessing the total tritiummore » breeding ratio in a fusion blanket. In addition, the reaction rates and the neutron spectrum are measured to provide test data for confirmation of calculation results. These data are compared among six different configurations of the experimental system. Consistency between the different techniques for each measured parameter is also tested among different experimental systems. The experimental results are compared with the calculations by DOT 3.5 using JENDL-3/PR1 and /PR2. The calculation differs from the experimental data by <10%, except for the beryllium zone. 25 refs., 21 figs., 11 tabs.« less
  • The chemical erosion behavior of graphite materials preexposed in the Tokamak Fusion Test Reactor (TFTR) as the bumper limiter has been investigated spectroscopically under deuterium plasma bombardment in the Plasma Interactive Surface Component Experimental Station-A (PISCES-A) facility. The deuterium plasma bombardment conditions are ion bombarding energy of 300 eV, ion flux of 1.7{times}10{sup 18} ions s{sup {minus}1} cm{sup {minus}2}, plasma density of 1.4{times}10{sup 12} cm{sup {minus}3}, electron temperature of 11 eV, and neutral pressure of 3{times}10{sup {minus}4} Torr. The chemical erosion yield is measured with calibrated CD-band spectroscopy during the temperaure ramp from 100 to 900 {degree}C at an averagemore » rate of {similar to}5 K/s. The materials used include virgin POCO graphite and graphite tile pieces from the redeposited and eroded areas of the bumper limiter of TFTR. The deuterocarbon formation rate from TFTR redeposits maximizes at {similar to}500 {degree}C. Essentially the same chemical erosion behavior is observed for TFTR-eroded and virgin graphites and is characterized by the compound peak, indicative of two erosion yield maxima at around 575 and 700 {degree}C. The maximum erosion yield for TFTR redeposits is found to be {similar to}15% higher than those of TFTR-eroded and virgin POCO graphites which is attributed to deuterium incorporated in the redeposited material. In addition, the removal behavior of redeposits by helium plasma bombardment has been studied. The removal rate is evaluated to be similar to the physical sputtering yield of carbon by helium. The surface morphology and surface composition have been analyzed with scanning electron microscopy and electron microprobe analysis along with these erosion yield measurements.« less
  • The chemical erosion behavior of graphite materials preexposed in the Tokamak Fusion Test Reactor (TFTR) as the bumper limiter has been investigated spectroscopically under deuterium plasma bombardment in the Plasma Interactive Surface Component Experimental Station-A (PISCES-A) facility. The deuterium plasma bombardment conditions are ion bombarding energy of 300 eV, ion flux of 1.7 x 10/sup 18/ ions s/sup -1/ cm/sup -2/, plasma density of 1.4 x 10/sup 12/ cm/sup -3/, electron temperature of 11 eV, and neutral pressure of 3 x 10/sup -4/ Torr. The chemical erosion yield is measured with calibrated CD-band spectroscopy during the temperature ramp from 100more » to 900 /sup 0/C at an average rate of /similar to/5 K/s. The materials used include virgin POCO graphite and graphite tile pieces from the redeposited and eroded areas of the bumper limiter of TFTR. The deuterocarbon formation rate from TFTR redeposits maximizes at /similar to/500 /sup 0/C. Essentially the same chemical erosion behavior is observed for TFTR-eroded and virgin graphites and is characterized by the compound peak, indicative of two erosion yield maxima at around 575 and 700 /sup 0/C. The maximum erosion yield for TFTR redeposits is found to be /similar to/15% higher than those for TFTR-eroded and virgin POCO graphites, which is attributed to deuterium incorporated in the redeposited material. In addition, the removal behavior of redeposits by helium plasma bombardment has been studied. The removal rate is evaluated to be similar to the physical sputtering yield of carbon by helium. The surface morphology and surface composition have been analyzed with scanning electron microscopy and electron microprobe analysis along with these erosion yield measurements. behavior« less
  • Ion implantation and ion beam analysis were used to examine bulk trapping and surface recombination for deuterium in Fe, Ni, and austenitic stainless steel. Irradiation-defect traps were characterized in the three metals, and substantially stronger traps were shown to be associated with small He bubbles. The rate of deuterium release at stainless steel and Fe surfaces was measured as a function of temperature and solution concentration. Trapping and surface recombination parameters were extracted by applying established theory for solute diffusion within a field of traps.