As energetic hydrogen atoms and ions impinge on a solid surface, some of the incident flux will be directly reflected, the remaining (penetrating) flux will thermalise inside the solid and will either become trapped or begin to diffuse in the lattice. Hydrogen that reaches the surface can be released as atoms by photon, electron, or ion impact desorption or as molecules by thermally activated molecular recombination. Thermal release of hydrogen atoms from a solid is not thermodynamically favored because of the high dissociation energy (4.5 eV) of the hydrogen molecule; thus, thermal release does not become significant until the temperatures reach ~ 2000 K.
Hydrogen isotope trapping and release by plasma facing materials control predominantly fuel retention and recycling in magnetic confinement fusion devices. Plasma-wall interactions involving hydrogenic particles have a major influence not only on the lifetime of the first wall and other plasma facing components but also on the fundamental properties of heated plasmas. In future D-T reactors, the hydrogen transport and desorption behaviour will control the tritium inventory in first walls and limiter/divertors and the plasma-driven tritium permeation into the coolant.
Hydrogen trapping and release in fusion materials have been studied extensively in the laboratory and in large scale fusion experiments. In parallel, a phenomenological theory based on simple diffusion in the presence of bulk and surface defects has been developed to account for the transport of hydrogen isotopes in and out of materials during and after exposure to hydrogenic plasmas.
In recent years, it has been endeavoured to reduce Zeff in fusion experiments and, consequently, there has been increased use of low-Z refractory plasma facing materials such as carbon and beryllium. However, in the course of the ITER design process the use of high-Z materials such as molybdenum or tungsten is considered in cases where a low plasma edge electron temperature can be maintained in a high recycle divertor.
Trapping and release of hydrogen in metals
Hydrogen retention and release characteristics for Beryllium
Hydrogen retention and release characteristics for Graphite
Hydrogen Behaviour in Molybdenum and Tungsten
Bulk diffusion, solubility and trapping of hydrogen and graphite at elevated temperatures
IAEA conducted a cooredinated research project on Tritium Inventory in Fusion Reactors in the period of 2002 to 2006. The summary of the CRP research is published in a joint paper in Fusion Science and Technology and a APID volume. Presentations on the following topics can be found in the IAEA A+M Homepage.
- Gamma irradiation of flakes retrieved from the JET fusion machine N. Bekris
- Studies of tritium retention in JET and of de-tritiation techniques P. Coad
- Recent results in dynamic retention and dust C. Skinner
- Tritium related investigations of hydrogen behavior in fusion materials A. Pisarev
- Overview of retention of hydrogen isotopes (H, D, T) and carbon erosion/ deposition in JT-60U T. Tanabe
- Study of the tritium content in materials of fusion reactors S. Artemov
- Ion-Driven Permeation of Deuterium through Tungsten M. Mayer
- Tritium retention and permeation in beryllium R. Causey
- Hydrogen isotopic effects on the chemical erosion of carbon A.A. Haasz
- PISCES-B mixed-material experiments R. Doerner
- Deuterium retention in carbon fibre composite irradiated with low-energy D ions J. Roth
- Deuterium retention in tungsten exposed to low-energy and high-flux clean and carbon-contaminated deuterium plasmas V.Kh. Alimov
More information on the related research acitivities by institutes worldwide can be found:
- Activities on Plasma-Material Interaction in Princeton Plasma Physics Laboratory, USA
- Activities on Plasma-Material Interaction in Russian Academy of Sciences, Russia
- Activities on Plasma-Material Interaction in Max-Planck-Institut für Plasmaphysik, EURATOM Association
- Activities on Plasma-Material Interaction in Sandia National Laboratories, USA
- Activities on Plasma-Material Interaction in Uzbekistan Academy of Sciences, Uzbekistan
- Activities on Plasma-Material Interaction in Forschungszentrum Karlsruhe, EURATOM Association
- Activities on Plasma-Material Interaction in EURATOM/UKAEA Fusion Association
- Activities on Plasma-Material Interaction in University of California at San Diego, USA
- Activities on Plasma-Material Interaction in University of Toronto, Canada
- Activities on Plasma-Material Interaction in Moscow Engineering and Physics Institute, Russia
- Activities on Plasma-Material Interaction in CEA/DSM/DRFC, Association EURATOM-CEA
- Activities on Plasma-Material Interaction in Kyushu University, Japan
- ↑ R. K. Janev and A. Miyahara , Plasma-material interaction issues in fusion reactor design and status of the database, Atomic and Plasma-Material Interaction Data for Fusion, v.1 p.123 (1991)
- ↑ R. A. Langley, J. Bohdansky, W. Eckstein, P. M ioduszewski, J. Roth, E. Taglauer, E. W. Thomas, H. Verbeek, K. L. Wilson, Data Compendium for Plasma-Surface interactions, Nucl. Fusion, Special Issue 1984, IAEA, Vienna
- ↑ C.H. Skinner, A.A. Haasz, V.Kh. Alimov, N. Bekris, R.A. Causey, R.E.H. Clark, J.P. Coad, J.W. Davis, R.P. Doerner, M. Mayer, A. Pisarev, J. Roth, T. Tanabe, Recent Advances on Hydrogen Retention in ITER's Plasma-Facing Materials: Beryllium, Carbon, and Tungsten, Fusion Science and Technology 54 (2008) 891-945
- ↑ http://www-amdis.iaea.org/CRP/