Alpha-Particle Effect in Ignition-Experiment-Grade Laser Fusion Pellets

(1)电子简并对α粒子加热的影响在压缩的最后阶段，ICF燃料球团的结构由一个低密度的中心热（<大于或等于4keV）火花和一个剩余的高密度的“冷”（<1keV）主燃料组成。燃料等离子体中的大多数电子处于简并态，受费米-狄拉克统计量的支配。在本研究中，我们首先研究了3.52 mev α粒子在简并等离子体球中的输运。与经典等离子体（即麦克斯韦等离子体）的情况相比，电子停止功率大大降低，因此α粒子的范围增加。因此，单个α粒子的减速受到实际燃烧ICF球团状态的强烈影响，然而，在中心点燃的火花沉积中产生的α粒子必须将其能量集中在点燃区域附近。它们不会深入到冷的主燃料中，在那里大多数电子是简并的。另一方面，中子在主燃料区沉积一定比例的能量，从而解决简并问题。因此，在燃料压缩的最后阶段，电子简并不影响热核燃烧。(2) α粒子输运的扩散近似的有效性研究发现，如果采用Levermore扩散系数并适当离散能量变量，采用近似扩散模型可以很好地计算ICF等离子体中α粒子的加热。我们还开发了一个二维粒子扩散代码。

(1) Effect of EIectron Degeneracy on alpha-Particle HeatingThe configuration of ICF fuel pellets at the final stage of compression consists of a central hot (<greater than or equal>4keV) spark with low density and a remaining "cold" (<1keV) main fuel with high density. Most of the electrons in the fuel plasma are in degenerate state, being governed by the Fermi-Dirac statistics. In this study we first examined the transport of 3.52-MeV alpha-particles in degenerate plasma spheres. Compared with the case of classical (i.e.Maxwellian) plasmas, the electronic stopping power substantially decreases and hence the range of the alpha-particles increases. The slowing-down of individual alpha-particle is thus strongly influenced by the state of eIn actual burning ICF pellets, however, the alpha-particles produced in the central ignited spark deposit must of their energy near the ignited region. They do not enter deeply into the cold main fuel where most of the electrons are degenerate. On the other hand, neutrons deposit a certain fraction of their energy in the main fuel region, thereby resolving the degeneracy. Thus, the electron degeneracy at he final stage of fuel compression does not affect the thermonuclear burning.(2) Validity of Diffusion Approximation for alpha-Particle TransportIt was found that the alpha-particle heating in ICF plasma can be well calculated using approximate diffusion model, if we adopt Levermore's diffusion coefficient and appropriately discretize the energy variable. We have also developed a two-dimensional alpha-particle diffusion code.