Studies on Re-emission Behavior of Hydrogen Isotopes from Wall Materials by Means of Ion Beam Analysis Techniques

本项目的目标是阐明氢同位素在壁材中重新发射的基本过程，并建立描述其在壁材中的动力学行为的模型，以预测和评价氦放电和主放电过程中氢同位素的循环。1990年和1991年，我们对与本项目有关的石墨材料进行了以下工作：1)用弹性反冲探测技术测量了室温下6×10^~(-15)/cm~2注入剂注入过程中和注入后石墨中氢同位素的深度分布。通过对两种深度剖面的比较，发现氢在石墨中的动态保留量很小而不能被检测到。2)在RT到250ﾟC的温度范围内，测量了3keV的H~+或D~+离子注入饱和的H~+或D~+离子在石墨中引起的氢同位素浓度衰变。H浓度越高，反应速度越快。这种同位素差异可以用离子诱导脱陷截面上的同位素差异和活化氢与俘获氢的局域分子复合速率常数之比和再俘获的速率常数之比来解释。3)在450600ﾟC温度范围内，测量了注入3keV H^+或D^+离子束直至浓度的石墨中氢同位素的浓度衰变，还发现H浓度的衰减快于D浓度的衰减。这种同位素差异还可以用活化氢之间的热脱陷、再俘获和局部分子复合的速率常数的表观差异来解释。4)根据再发射实验中获得的再发射曲线，用描述其动力学行为的质量平衡方程从理论上预测了注入到石墨中的氢同位素的热脱附谱。结果表明，采用等温重发射实验中得到的物理参数，氢分子的热脱附谱计算结果与实验结果吻合较好。较少

Goal of this project is to clarify the elementary processes in the re-emission of hydrogen isotopes from wall materials and to establish the model describing their dynamic behavior in the wall materials for prediction and evaluation of hydrogen isotopes recycling during He discharge and main discharged.In 1990 and 1991, we have performed following tasks for graphite materials concerning with this project.1) Depth profiles of hydrogen isotopes in graphite during and after implantation at flux of 6x10^<15>/cm^2s at room temperature have been measured by means of the elastic recoil detection technique. It has been found from comparison between both depth profiles that dynamic retention of hydrogens in graphite is so small not to be detected.2) The concentration decays of hydrogen isotopes in graphite, implanted with 3 keV H^+_ or D^+_ ion beams up to saturation, induced by 1.5 MeV He^+ ion bombardment have been measured at temperatures from RT to 250ﾟC. It has been found that the decay of … More H concentration is faster than of D concentration. This isotopic difference is shown to be explained in terms of isotopic difference in the ion-induced detrapping cross-section and the ratio of the rate constants of local molecular recombination between an activated hydrogen and a trapped one and retrapping.3) The concentration decays of hydrogen isotopes in graphite, implanted with 3 keV H^+_ or D^+_ ion beams up to concentration, induced by isothernal annealings have been measured at temperatures from 450 to 600ﾟC It has been also found that the decay of H concentration is faster than that of D concentration. This isotopic difference is also shown to be explained in terms of istopic difference in the rate constants of thermal detrapping, retrapping and local molecular recombination between activated hydrogens.4) Using the re-rmission profiles obtained in the re-emission experiment, it is shown that the thermal desorption spectrum on hydrogen isotopes implanted into graphite is theoretically predicted using the mass balance equations describing their dynamic behaviors. It is found that the calculated thermal desorption spectrum of hydrogen molecule agrees well with the experimental ones when the physical parameters obtained in the isothermal re-emission experiment are used. Less