量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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Laser-driven ion acceleration has been one of the most active areas of research over approximately the past decade, because accelerated multi-MeV ion beams have unique properties that can be employed in a broad range of applications including nuclear science, hadron cancer therapy, and fast ignition for inertial confinement fusion. The recent advancements in laser-driven ion acceleration techniques using thin foil targets allow the maximum proton energies close to 100 MeV. From a view point of practical applications, high-purity proton beams with high reproducibility are quite advantageous. In experiments using thin foil targets, however, protons from surface contaminants along with the high-z component materials are accelerated together, making the production of impurity-free proton beams unrealistic.
Here we introduce a micron-size hydrogen cluster, composed of 10^8-10 hydrogen molecules, as a target to generate impurity-free, highly-reproducible, and robust multi-MeV proton beams. Because of the recent progress in intense laser technology, the advanced PW class lasers can now achieve intense laser fields around 10^22 W/cm^2; with such fields, all the electrons inside the micron-size hydrogen cluster up to 3.0 μm in diameter can be fully stripped off, resulting in a pure Coulomb explosion with a pronounced increase in accelerated maximum proton energies scaled as Emax = 276(d/2)2 MeV, where d is a diameter of clusters. For example, 100 MeV protons could be produced via the Coulomb explosion of the 1.2 μm diameter hydrogen cluster when irradiated by a laser pulse with a peak intensity of 1.6 × 10^21 W/cm^2. The robust nature of the Coulomb explosion mechanism offer an additional advantage for practical applications.
Generation of high-repetitive, multi-MeV, pure proton beams via Coulomb explosion of micron-size hydrogen clusters
