Z箍缩动态黑腔驱动靶丸内爆动力学

利用Z箍缩动态黑腔驱动靶丸内爆是实现惯性约束聚变可能的技术途径之一.聚龙一号装置已开展的动态黑腔实验初步表明形成了有效的动态黑腔辐射场,为驱动靶丸内爆研究奠定了重要基础.针对聚龙一号装置驱动条件,通过建立包含柱形动态黑腔与球形靶丸的柱球耦合物理模型,利用二维辐射磁流体力学程序,对Z箍缩动态黑腔驱动靶丸内爆动力学过程进行了数值模拟研究,获得了丝阵等离子体内爆、丝阵等离子体与泡沫转换体相互作用、冲击波产生和黑腔辐射传输、辐射烧蚀和燃料压缩的完整过程.在此基础上,研究了靶丸赤道面和两极的辐射源均匀性及燃料压缩对称性.结果表明,由于在泡沫转换体中的辐射传输以及黑腔-靶能量耦合过程,靶丸赤道面与两极辐射波形存在一定的时间差和峰值差,造成燃料压缩不对称.若减小靶丸半径,可以提高燃料压缩的对称性,但靶丸半径很小时聚变产额也较低;靶丸半径较大时,由于靶丸赤道面和两极辐射场时间和温度峰值的较大差异,燃料压缩呈现更为明显的不对称性.

Numerical studies on dynamics of Z-pinch dynamic hohlraum driven target implosion

The dynamic hohlraum is a possible approach to driving inertial confinement fusion.Recently, dynamic hohlraum experiments on the primary test stand (PTS) facility were conducted, and preliminary results show that a dynamic hohlraum is formed, which can be used for driving target implosion.In this paper, the implosion dynamics of Z-pinch dynamic hohlraum driven target implosion with the drive current of PTS facility is numerically investigated.A physical model is established, in which a dynamic hohlraum is composed of a cylindrical tungsten wire-array and a CHO foam converter, and the target is composed of a high density CH ablator and low density DT fuel.The drive current is calculated by an equivalent circuit model, and the integrated simulations in (r, Z) plane by using a two-dimensional radiation magneto-hydrodynamics code are performed to describe the overall implosion dynamics.It is shown that the wire-array plasma is accelerated in the run-in stage, and in this stage the target keeps almost immobile.As the accelerated wire-array plasma impacts onto the low-density foam converter, a local region with high temperature and high pressure is generated near the W/CHO boundary due to energy thermalization, and this thermalization process will last several nanoseconds.This high temperature region will launch a strongly radiating shock.At the same time, high temperature radiation also appears and transfer to the target faster than the shock.When the high temperature radiation transfers to the surface of the target, the ablator is heated and the ablated plasma will expand outward, and a high-density flying layer will also be generated and propagate inward.After the high-density layer propagates to the ablator/fuel boundary, the DT fuel will be compressed to a high-density and high-temperature state finally.At the same time, the cylindrical shock, which is generated from the impact of the wire-array plasma on the foam converter, will gradually propagate to the ablator plasma.After it propagates over the converter/ablator boundary, it will be decelerated by the ablation pressure, which is beneficial to isolating the fuel compression from the direct cylindrical shock.It is shown that though the trajectories of the outer boundaries of the ablator at the equator and at the poles are completely different due to shock interaction at the equator, the fuel compression is nearly uniform due to radiation compression.It is shown that the asymmetry of fuel compression is mainly caused by the non-uniformity of the hohlraum radiation at the equator and at the poles.Generally, there are two differences between the radiation temperatures at the equator and at the poles, namely the time difference due to the finite velocity of radiation transfer, and the peak temperature difference due to energy coupling.If the target is small, the peak radiation temperature at the equator is almost the same as at the pole.The fuel at the equator is first compressed just because the radiation first transfers to the target equator.As the size of the target is increased, the difference in peak radiation temperature will be more serious, thus causing weaker fuel compression at the equator than at the poles.Certainly, if the target size is too large, the cylindrical shock will directly interact on the target at the equator, resulting in complete asymmetry at the equator with respect to the shock at the poles, which should be avoided.Furthermore, it is shown that as the target size is increased, the final neutron yield will first increase and then decrease, which means that there is a relatively optimal size selection for target implosion.