Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, United Kingdom.
Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
Phys Rev Lett. 2013 Feb 15;110(7):075001. doi: 10.1103/PhysRevLett.110.075001. Epub 2013 Feb 14.
The sensitivity of inertial confinement fusion implosions, of the type performed on the National Ignition Facility (NIF) [1], to low-mode flux asymmetries is investigated numerically. It is shown that large-amplitude, low-order mode shapes (Legendre polynomial P(4), resulting from low-order flux asymmetries, cause spatial variations in capsule and fuel momentum that prevent the deuterium and tritium (DT) "ice" layer from being decelerated uniformly by the hot spot pressure. This reduces the transfer of implosion kinetic energy to internal energy of the central hot spot, thus reducing the neutron yield. Furthermore, synthetic gated x-ray images of the hot spot self-emission indicate that P(4) shapes may be unquantifiable for DT layered capsules. Instead the positive P(4) asymmetry "aliases" itself as an oblate P(2) in the x-ray images. Correction of this apparent P(2) distortion can further distort the implosion while creating a round x-ray image. Long wavelength asymmetries may be playing a significant role in the observed yield reduction of NIF DT implosions relative to detailed postshot two-dimensional simulations.
数值研究了惯性约束聚变内爆（如在国家点火装置 [1] 上进行的内爆）对低阶模式通量不对称性的敏感性。结果表明，大振幅、低阶模式形状（由低阶通量不对称性产生的勒让德多项式 P(4)）导致了胶囊和燃料动量的空间变化，从而阻止了氘和氚（DT）“冰”层被热斑压力均匀减速。这降低了内爆动能向中心热斑内能的传递，从而降低了中子产额。此外，对热斑自发射的合成门控 X 射线图像的分析表明，对于 DT 层状胶囊，P(4)形状可能无法量化。相反，正 P(4)不对称性在 X 射线图像中“伪影”为扁长形的 P(2)。对这种明显的 P(2)失真进行校正可能会在创建圆形 X 射线图像的同时进一步扭曲内爆。长波长不对称性可能在 NIF DT 内爆的观察到的产额降低中发挥了重要作用，这与详细的后射击二维模拟相比。
