TY - JOUR
T1 - Evolution of surface melt damage, its influence on plasma performance and prospects of recovery
AU - Coenen, J. W.
AU - Krieger, K.
AU - Lipschultz, B.
AU - Dux, R.
AU - Kallenbach, A.
AU - Lunt, T.
AU - Mueller, H. W.
AU - Potzel, S.
AU - Neu, R.
AU - Terra, A.
PY - 2013/7
Y1 - 2013/7
N2 - Experiments have been carried out in the TEXTOR, ASDEX Upgrade (AUG) and Alcator C-Mod (C-Mod) tokamaks to study melt-layer motion, macroscopic W-erosion from the melt as well as the changes of material properties such as grain-size and voids. In addition the effect of multiple exposures is studied to judge the potential amelioration of inflicted melt damage. The parallel heat flux at the radial position of the PFCs in the plasma ranges from around q∥ ∼45 MW/m2 at TEXTOR up to q∥ ∼ 500 MW/m 2 at C-Mod which covers scenarios close to ITER parameters, allowing samples to be exposed and molten even at shallow divertor angles. Melt-layer motion perpendicular to the magnetic field is observed consistent with a Lorentz-force originating from thermoelectric emission of the hot sample. While melting in the limiter geometry at TEXTOR is rather quiescent causing no severe impact on plasma operation, exposure in the divertors of AUG and C-Mod shows significant impact on operation, leading to subsequent disruptions. The power-handling capabilities are severely degraded by forming exposed hill structures and changing the material structure by re-solidifying and re-crystallizing the original material. Melting of W seems highly unfavorable and needs to be avoided especially in light of uncontrolled transients and misaligned PFCs.
AB - Experiments have been carried out in the TEXTOR, ASDEX Upgrade (AUG) and Alcator C-Mod (C-Mod) tokamaks to study melt-layer motion, macroscopic W-erosion from the melt as well as the changes of material properties such as grain-size and voids. In addition the effect of multiple exposures is studied to judge the potential amelioration of inflicted melt damage. The parallel heat flux at the radial position of the PFCs in the plasma ranges from around q∥ ∼45 MW/m2 at TEXTOR up to q∥ ∼ 500 MW/m 2 at C-Mod which covers scenarios close to ITER parameters, allowing samples to be exposed and molten even at shallow divertor angles. Melt-layer motion perpendicular to the magnetic field is observed consistent with a Lorentz-force originating from thermoelectric emission of the hot sample. While melting in the limiter geometry at TEXTOR is rather quiescent causing no severe impact on plasma operation, exposure in the divertors of AUG and C-Mod shows significant impact on operation, leading to subsequent disruptions. The power-handling capabilities are severely degraded by forming exposed hill structures and changing the material structure by re-solidifying and re-crystallizing the original material. Melting of W seems highly unfavorable and needs to be avoided especially in light of uncontrolled transients and misaligned PFCs.
UR - http://www.scopus.com/inward/record.url?scp=84885483254&partnerID=8YFLogxK
U2 - 10.1016/j.jnucmat.2013.01.005
DO - 10.1016/j.jnucmat.2013.01.005
M3 - Article
AN - SCOPUS:84885483254
SN - 0022-3115
VL - 438
SP - S27–S33
JO - Journal of Nuclear Materials
JF - Journal of Nuclear Materials
IS - SUPPL
ER -