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

(1)电子简并对α粒子热的影响ICF燃料芯块在压缩的最后阶段由一个密度较低的中心热(&lt；大于或等于&gt；4keV)火花和一个密度较高的“冷”(&lt；1keV)主燃料组成。燃料等离子体中的大多数电子都处于简并态，受费米-狄拉克统计的支配。在这项研究中，我们首先研究了3.52 MeVα粒子在简并等离子体球中的输运。与经典(即麦克斯韦的)等离子体相比，电子阻止功率大大降低，从而增加了α粒子的射程。因此，单个α粒子的减速受实际燃烧的ICF弹丸中电子状态的强烈影响，然而，在中心点火的火花沉积中产生的α粒子必须在点火区域附近获得能量。它们不会深入到大多数电子都简并的冷主燃料中。另一方面，中子在主燃料区储存了一定比例的能量，从而解决了简并问题。因此，燃料压缩最后阶段的电子简并不会影响热核燃烧。(2)α粒子输运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化能量变量，用近似扩散模型可以很好地计算ICF等离子体中的α粒子加热。我们还开发了一个二维α粒子扩散程序。

(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.