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

(1)电子简并对α粒子加热的影响ICF燃料芯块在压缩末级的构型由中心<greater than or equal>低密度热火花（4keV）和剩余的高密度冷主燃料（&lt;1 keV）组成。燃料等离子体中的大部分电子处于简并态，受费米-狄拉克统计的控制。在这项研究中，我们首先研究了3.52 MeV α粒子在简并等离子体球中的传输。与经典（即麦克斯韦）等离子体的情况相比，电子阻止本领大大降低，因此α粒子的范围增加。在实际燃烧的ICF弹丸中，单个α粒子的慢化受弹丸状态的影响很大，而在中心点火火花存款中产生的α粒子的能量必须在点火区域附近。它们不会深入到冷的主燃料中，那里的大多数电子都是简并的。另一方面，中子存款的一部分，他们的能量在主燃料区，从而解决了简并。因此，在燃料压缩的最后阶段的电子简并不影响热核燃烧。(2)扩散近似对α粒子输运的有效性研究发现，如果采用Levermore的扩散系数，并对能量变量进行适当的离散，则可以用近似扩散模型很好地计算ICF等离子体中α粒子的加热。我们还开发了一个二维α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.