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Effects of long rarefied plasma on fast electron generation for FIREX-I targets

Published online by Cambridge University Press:  13 December 2011

H. Sakagami ,
A. Sunahara ,
T. Johzaki  and
H. Nagatomo
H. Sakagami*
Affiliation:
Fundamental Physics Simulation Division, National Institute for Fusion Science, Toki, Japan
A. Sunahara
Affiliation:
Institute for Laser Technology, Suita, Japan
T. Johzaki
Affiliation:
Institute for Laser Technology, Suita, Japan
H. Nagatomo
Affiliation:
Institute of Laser Engineering, Osaka University, Suita, Japan
*
Address correspondence and reprint requests to: H. Sakagami, Fundamental Physics Simulation Division, National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan. E-mail: sakagami.hitoshi@nifs.ac.jp
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Abstract

Long-scale preformed plasmas are generated inside the cone by the pre-pulse of the heating laser in the cone-guided fast ignition scheme and it is found that coupling efficiency from the heating laser to fast electrons especially suitable for core heating is drastically reduced by the preformed plasmas. To mitigate this serious problem, an extremely thin film is suggested to cover the entrance of the cone. This method, however, introduces long rarefied plasmas around the entrance of the cone and the main pulse must propagate through these plasmas. Therefore, fast electron characteristics produced by the main pulse could be affected, and effects of long rarefied plasmas on fast electron generation are investigated. It is found that the electron beam intensity becomes larger than that without the rarefied plasma, but the energy coupling rate from the heating laser to the core decreases due to lack of appropriate electrons for core heating. To achieve less than 10% degradation of the core electron temperature, the thin film must be expanded by irradiation of the pre-pulse so that the length and the density of rarefied plasmas become less than 500 µm and one-tenth of the critical density. A thickness of the thin film can be determined by these criteria and the intensity of the pre-pulse.

Keywords

Cone-guided targetFast electronFast ignitionIntegrated simulation
Type
Research Article
Information
Laser and Particle Beams , Volume 30 , Issue 1 , March 2012 , pp. 103 - 109
Copyright
Copyright © Cambridge University Press 2011

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References

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