The experimental results of low pressure supersonic molecular beam injection (SMBI) fuelling on the HL-2A closed divertor indicate that during the period of pulsed SMBI the power density convected at the target plate surfaces was 0.4 times of that before or after the beam injection. An empirical scaling law used for the SMBI penetration depth for the HL-2A plasma was obtained. The cluster jet injection (CJI) is a new fuelling method which is based on and developed from the experiments of SMBI in the HL-1M tokamak. The hydrogen clusters are produced at liquid nitrogen temperature in a supersonic adiabatic expansion of moderate backing pressure gases into vacuum through a Laval nozzle and are measured by Rayleigh scattering. The measurement results have shown that the averaged cluster size of as large as hundreds of atoms was found at the backing pressures of more than 0.1 MPa. Multifold diagnostics gave coincidental evidence that when there was hydrogen CJI in the HL-2A plasma, a great deal of particles from the jet were deposited at a terminal area rather than uniformly ablated along the injecting path. SMB with clusters, which are like micro-pellets, will be of benefit for deeper fuelling, and its injection behaviour was somewhat similar to that of pellet injection. Both the particle penetration depth and the fuelling efficiency of the CJI were distinctly better than that of the normal SMBI under similar discharge operation. During hydrogen CJI or high-pressure SMBI, a combination of collision and radiative stopping forced the runaway electrons to cool down to thermal velocity due to such a massive fuelling.
We demonstrate experimentally the efficient fusion neutron generation from Coulomb explosion ͑CE͒ of laser irradiated large-size heteronuclear deuterated methane clusters. A conversion efficiency of 2.1 ϫ 10 6 neutrons/ J of incident laser energy is obtained with a 120 mJ, 70 fs laser pulse. It is 50 times higher than that of homonuclear deuterium clusters of similar size. This enhancement is attributed to the significant increase in the deuteron kinetic energies by fourfold due to energetic boosting and overrun effects during CE of heteronuclear clusters. The yield of 5.5ϫ 10 6 neutrons per pulse is obtained with a 100 TW, 50 fs driving laser pulse at an intensity of 1.5ϫ 10 19 W / cm 2 . This work may facilitate the development of a high-flux The generation of deuterium-deuterium ͑DD͒ fusion neutrons from Coulomb explosion ͑CE͒ of laser-heated cryogenic deuterium clusters ͑D 2 ͒ N was first demonstrated by Ditmire et al. in 1999 ͓1͔ with a high-repetition-rate tabletop laser; an efficiency of about 10 5 fusion neutrons/ J of incident laser energy was achieved, which was close to the efficiency of large-scale laser-driven fusion experiments ͓2,3͔. This kind of short ͑subnanosecond͒ bursts of monoenergetic fusion neutrons could find wide applications in materials science ͓4͔ such as high spatial resolution neutron radiography and time-resolved study of radiation damage which is of particular importance for developing future fusion energy reactor. However, the conversion efficiency of neutron generation should be improved dramatically to be 10 7-8 neutrons/ J of incident laser energy ͓5͔. Extensive researches have been devoted to investigate the fusion dynamics in laser-cluster interactions and the temporal and spatial characterizations of fusion neutron emission, as well as to search for higher neutron yields ͓6-19͔. The effects of the ͑D 2 ͒ N cluster size, the laser energies, and focusing conditions were studied by Zweiback et al. to optimize fusion neutron yields ͓7͔. However, the average kinetic energies ͑KEs͒ of deuterons from explosion of ͑D 2 ͒ N clusters were reported to be in the range of 2.5-7 keV ͓6,7,13-15͔ which are still much lower than the optimal KEs in the range of 40-100 keV for an efficient DD fusion.Last and Jortner proposed a scheme to enhance the deuterons' KEs by using clusters of heteronuclear deuterium containing molecules, e.g., ͑D 2 O͒ N and ͑CD 4 ͒ N ͓9,10,12,16,17͔. For the Coulomb explosion of the heteronuclear clusters, the light deuterons' KEs can be greatly enhanced due to kinematic overrun effect and the energetic boosting caused by the large ionic charge of the heavy ions inside the cluster ͓12,16,17͔. Grillon et al. used deuterated methane clusters ͑CD 4 ͒ N as a novel target in a table-top nuclear fusion experiment, demonstrating a conversion efficiency of about 1 ϫ 10 4 neutrons/ J of incident laser energy ͓11͔. Meanwhile, an independent theoretical work on ͑CD 4 ͒ N made by Last and Jortner predicts that the neutron yields with the heteronuclear clusters are 3.7ϫ 10 5 neutr...
The explosion dynamics of hydrogen clusters driven by an ultrashort intense laser pulse has been analyzed analytically and numerically by employing a simplified Coulomb explosion model. The dependence of average and maximum proton kinetic energy on cluster size, pulse duration, and laser intensity has been investigated respectively. The existence of an optimum cluster size allows the proton energy to reach the maximum when the cluster size matches with the intensity and the duration of the laser pulse. In order to explain our experimental results such as the measured proton energy spectrum and the saturation effect of proton energy, the effects of cluster size distribution as well as the laser intensity distribution on the focus spot should be considered. A good agreement between them is obtained.
We study the carbon-dope aluminum clusters by using time-of-flight mass spectrum experiments and ab initio calculations. Mass abundance distributions are obtained for anionic aluminum and aluminum-carbon mixed clusters. Besides the well-known magic aluminum clusters such as Al In recent years, clusters and cluster-based materials have been a field of intensive research due to both fundamental and technological importance 1-7 . The structural, electronic, magnetic, and optical properties of the clusters are different from those of constitute atoms or bulk phase and depend sensitively on the size and composition of the cluster 1-3 . It is desirable to assemble the cluster-based materials from properly designed clusters so that the unique properties of these individual clusters can be retained 6,7 . To be a building block of clusterassembled materials, the cluster should be highly stable and relatively unreactive. Thus, the clusters would interact weakly with each other and maintain their identities when they are brought together in the cluster-assembled solids. A well-known example is the C 60 solids 8 . Besides C 60
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