Thermal and Mechanical Analysis of ITER-Relevant LHCD Antenna Elements

1. Thermal and Mechanical Analysis of ITER-Relevant LHCD Antenna Elements L.Marfisi1, M.Goniche1, C.Hamlyn-Harris2, J.Hillairet1, J.F. Artaud1, Y.S. Bae3, J. Belo4, G. Berger-By1, J.M. Bernard1, Ph. Cara1, A. Cardinali5, C. Castaldo5, S. Ceccuzzi5, R. Cesario5, J. Decker1, L. Delpech1, A. Ekedahl1, J.Garcia1, P. Garibaldi1, D. Guilhem1, G.T. Hoang1, H. Jia6, Q.Y. Huang6, F. Imbeaux1, F. Kazarian2, S.H. Kim1, Y. Lausenaz1, R. Maggiora7, R. Magne1, S. Meschino8, D. Milanesio7, F. Mirizzi5, W. Namkung9, L. Pajewski8, L. Panaccione8, Y. Peysson1, A. Saille1, G. Schettini8, M. Schneider1, P.K. Sharma1,10, A.A. Tuccillo5, O. Tudisco5, G. Vecchi8, S. R. Villari5, K. Vulliez1, Y. Wu6, Q. Zeng6 1CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 2ITER Organization, CS 90 046, 13067 Saint-Paul-Les-Durance, France. 3National Fusion Research Institute, Daejeon, Korea. 4Associaçao Euratom-IST, Centro de Fusao Nuclear, Lisboa, Portugal . 5Associazione Euratom-ENEA sulla Fusione, CR Frascati, Roma, Italy. 6Institute of Plasma Physics, CAS, Hefei, Anhui, China. 7Politecnico di Torino, Dipartimento di Elettronica, Torino, Italy. 8Roma Tre University, Roma, Italy. 9Pohang Accelerator Laboratory, Pohang Univ. of Science and Technology, Pohang, Korea. 10Permanent address: Institute for Plasma Research, Bhat,Gandhinagar, Gujarat, India PAM front face grill LH PAM antenna 5 GHz 500 kW CW window A Lower Hybrid Current Drive PAM antenna is envisaged on ITER. In the frame of an EFDA task, design studies have been carried out. Mechanical studies of 2 critical elements are presented. The front face is a multilayer assembly. It faces thermal loads from plasma radiations, fast ions, and RF losses, accounting for total power of 1.25 MW/m² and neutron volume heating of 3MW/m3. As a plasma facing component, it is designed with a beryllium coating. The window is a brazed assembly of different materials. It is a critical safety importance component since its ceramic is also the first tritium barrier. According to HFSS simulations, when operating, up to 1.5kW of RF losses heat up the Beryllium Oxide ceramic. RF losses distribution in the ceramic The manufacturing process is expected to create high residual stresses that are annealed at 500°C. Analysis shows that the assembly can withstand them. The beryllium parts cannot exceed a temperature limit of 650°C for safety concerns. The analysis of the manufacturing process shows substantial residual stresses originating from a problematic pinching phenomenon on the ceramic. With values (152MPa) exceeding the static fatigue limit of 50 MPa for BeO. This can be solved through peripheral pre-compression of the ceramic disk. Thermal analysis shows that our design comfortably fulfills temperature requirements (Tmax = 493°C in Beryllium) with water-cooling flow (4.8m/s) and pressure drop (29.6 kPa) consistent with ITER port limits (1MPa). Pinching: critical tensile stresses on ceramic edges 70 MPa pre-compression Mechanical analysis, including in-pipe water cooling pressure shows mechanical resistance. Most critical stresses were spotted in the stainless steel (170 MPa) and were well below resistance criterion (450 MPa) . The dielectric losses where reduced through RF optimization to 540 W (see poster P.1-15 ) and the subsequent temperature elevation and thermal stresses became low enough for us to keep the BeO as a dielectric material for the window: tensile stresses in the ceramic (31MPa) where well lower than the 50 MPa static fatigue limit of BeO. Conclusion: Both studies allow to move forward and focus on other critical issues, such as manufacturing processes and R&D associated programs including high power RF tests of mock-ups. This work, supported by the European Communities under the contract of Association between EURATOM and CEA, was carried out within the framework of the EFDA task HCD-08-03-01. The views and opinions expressed herein do not necessarily reflect those of the European Commission.