K. Horioka

K." Kamada

M. "Ogawa

M. Nakaijima

T. Aoki

National Institute for Fusion Science (NIFS-Repository)

§ 14. High Density Plasma Target for Beam-Plasma Interaction Experiments Ogawa, M., Nakaijima, M., Horioka, K., Aoki,T. (Dept. Energy Sci. Tokyo Inst. Tech.) Kamada, K. Interaction of heavy ions with dense plasma is important as a fundamental process concerning the heavy-ion inertial confinement fusion. Enhancement of energy loss of heavy ions in the plasma compared to the cold matter was first predicted by theory many years ago and recently observed by several groups. The enhancement of stopping power is governed by the effective charge state Zerf of the ions. The ions passing through the plasma interact with free electrons so that the effective charge state is determined by the balance of ionization and recombination. Interesting phenomena are expected for a high-density plasma of fie > 1019cm-3 and for low-energy beams. So we develop plasma targets of high-density which are available for the in-beam experiments. We report a laser-plasma target, which is installed to a beam line of the TIT 1.7 MV tandem. A TEA C02 laser of 31 energy irradiates a polyethylene plate to produce plasma. The C02 laser has a wave length of 10 ~m. Its cutoff density is 1.1x1019 em -3. The amount of ablation is estimated by weighing the polyethylene plate after several hundred shots. The number of ablated atoms is about 1017 per shot. The expanding plasma is optical! y diagnosed as a function of time and space. The electron density distribution is obtained from the Stark broadening of Ha and H~ lines. Fig.1 shows an example of density distribution along the laser beam axis. The density decreases as a power function of distance from the polyethylene surface between 0.2 and 5 mm and then keeps a constant level up to 30 mm. The decay part is consistent with the ablating expansion. The plateau is understood in terms of plasma formed by post-irradiation of ablating matter. The plateau part is a candidate of plasma target with a uniform density distribution. t=1.6 ~s ························································r·························· ... ......................... r .................... ~.f .. : .........  1016 L-~~~Ull--~~~~--~~~~ 0.1 1 10 100 Distance from Polyethylene Surface [mm] Fig.1 Electron density distribution. Fig.2 shows a schematic layout of the apparatus for measurement of charge stripping experiment. A Li+ beam of 0.9 MeV is injected to the laser plasma. Charge stripped ions of Li++ and Li+++ are analyzed with a magnet and detected with a plastic scintillator. This experiment is now progressing. Video Camera C02 Laser Target Chamber Magnet Fig. Layout of charge stripping experiment. 129 

High Density Plasma Target for Beam-Plasma Interaction Experiments

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