2004 Fiscal Year Final Research Report Summary
Helium Retention and Release Characteristics of Multi-layer Pebbles for Pebble Drop Devertor
| Project/Area Number |
13308024
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear fusion studies
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| Research Institution | Osaka University |
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Principal Investigator |
NISHIKAWA Masahiro Osaka University, Graduate School of Engineering, Department of Electronic, Information Systems and Energy Engineering, Professor, 大学院・工学研究科, 教授 (50029287)
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| Co-Investigator(Kenkyū-buntansha) |
UEDA Yoshio Osaka University, Graduate School of Engineering, Department of Electronic, Information Systems and Energy Engineering, Associate Professor, 大学院・工学研究科, 助教授 (30193816)
OHTSUKA Yusuke Osaka University, Graduate School of Engineering, Department of Electronic, Information Systems and Energy Engineering, Research Associate, 大学院・工学研究科, 助手 (70294048)
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| Project Period (FY) |
2001 – 2004
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| Keywords | Pebble Divertore / Pumping and Recycling Performance / Helium Pumping / Pebble Curtain / Plasma Shielding / ECR discharge / Presheath / Multi-layer Pebble |
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| Research Abstract |
One of the notable characteristics of a pebble drop divertor system is pumping performance of hydrogen isotopes and helium. In order to develop optimum fuel pumping and recycling system, the following subjects were studied : retention and release characteristics of hydrogen and helium by multi-layer pebbles, forming pebble curtain by pebble dropping through thin slits and evaluation of plasma shielding effects, plasma shielding mechanism by pebbles in plasma flow.
According to helium retention experiments, transient helium release from graphite samples decrease with increasing irradiation temperature in the case that irradiation temperature and desorption temperature was the same. Almost no helium retention was observed over 700 K even if transient release of He under high flux ion beam irradiation was taken into consideration. Helium pumping performance of the pebble drop divertor system was estimated from the experimental results and compared with a helium generation rate of ARIES-AT
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tokamak reactor concept. It was found that the pebble drop divertor system has enough pumping performance even at the pebble temperature of 673 K, which is slightly less than the retention limit ( 700K).
For the development of pebble falling system, the width of the slit for pebble discharge is determined to more than 3 cm in the case that the shading rate of incoming divertor plasma is more than 90%. This slit size does not cause any problem for the installation of the pebble falling system in actual fusion reactors.
For the study of plasma shielding mechanism by pebbles, simulation experiments by using an ECR plasma source was performed. In the experiments, hydrogen plasma produced by ECR discharge was diffused along magnetic field lines to a constant field region (100〜500 G). Then circular plates with the diameter of 2 cm and 5 cm (simulator for divertor pebbles) were inserted in the constant field plasma region to investigate the effects of pebbles on plasma parameters. Two dimensional distributions (radial and axial) of plasma parameters such as density, temperature, and potential were measured by a Langmuir probe. This measurement clearly showed two dimensional structure of the plasma presheath around the circular plates. Simulation results roughly agree with experimental results in the discharge gas pressure of 10 m Torr. Less
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Research Products
(14 results)
