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We investigated the relationship between heavy-ion composition variability in gradual solar energetic particle (SEP) events and the source regions of the associated interplanetary magnetic field (IMF) along which these SEPs are transported. In particular, we found that the SEP elemental composition has a positive correlation with the unsigned photospheric magnetic field strength around the IMF footpoints. Furthermore, the IMF source region can be generally categorized into two classes, depending on whether the associated solar wind, and correspondingly the footpoints of the open magnetic field along which the SEPs are transported, are from a coronal hole (CH) near an active region (an 'AR field-source') or from a CH without an AR in its close proximity (a 'CH field-source'). This study is based on 24 events observed in years 1998 and 2003-2006. We present in this paper the results for Fe/O as an example, and show that the observed SEP Fe/O ratio at 3-30 MeV/nucleon is preferentially enhanced in the case of AR field-source. By contrast, the distributions of Fe/O for the in-situ solar-wind thermal particles in these time intervals are essentially indistinguishable between the two field-sources. Our results suggest that suprathermal ions are the preferred seed particles for shock acceleration, and the composition of these suprathermals depends on the magnetic field where they are generated, with suprathermals associated with active regions, i.e. stronger photospheric magnetic field, having larger heavy-ion enhancements than suprathermals associated with coronal holes with weak magnetic field. These results open a new window in understanding the origin and production of the suprathermal seed particles for SEPs. [ABSTRACT FROM AUTHOR]

NIF's ignition campaign has attracted a great attention recently due to its significance to the future of fusion researches worldwide. Recent experiment results have demonstrated both hopes as well as challenges faced by the NIF team. One of the greatest challenges is to achieve desired areal density ρR for both fuel and hot-spot regions so that a self-sustained TN burn could be initiated and maintained. Unfortunately, the recent results from the NIF's ignition shots indicated that the desired equivalent areal density ρR has not been reached during the ignition time for a self-sustained thermonuclear burn. In this presentation, We will propose a novel approach to achieve a greater ρR in the fuel and especial hot-spot in additional to what the NIF can achieve by utilizing radiative cooling mechanism in the end of the implosion phase to give both the hot-spot and fuel an additional push so that a higher areal density ρR can be reached just before ignition. The proposal of radiative cooling is counter intuitive at the first sight. In the past, the radiative cooling caused by mixing of high Z material into the gas region was considered as a degradation factor to the performance of ICF capsule. However, in this presentation, we will demonstrate that with a proper implementation of radiative cooling during final implosion phase it will enhance the performance margin dramatically. The two immediate benefits of the radiation cooling are: (a) the cooling of the fuel in the final implosion phase reduces pressure of the fuel so that a better compression can be achieve; and (b) the radiation cooling reduces the ion temperature of the fuel and gas momentarily which in turn results in a delay of thermonuclear burn ignition such that additional few picoseconds are acquired to implode the capsule further. Moreover, another important feature of this approach is that all the previous researches and efforts of the NIF campaign can be fully utilized, for example, laser pulse shaping, holhraum physics, laser-plasma interaction, even capsule design [1,2,3], since the only difference this new approach is to add an additional doping in the gas region. Over 38% of improvement of gas (hot-spot) ρR and 50% increase of the yield rate compared to that of the NIF baseline point design (Rev. 5B) have been achieved using this approach with the identical drive conditions. [ABSTRACT FROM PUBLISHER]