激光驱动黑腔 X 射线源辐照泡沫靶的等离子体特性及加热机制模拟研究

The plasma environment plays a crucial role in determining the energy deposition behavior of ion beams and the resulting nuclear reaction yields. The generation of controllable and spatially uniform plasmas under laboratory conditions is therefore essential for precise investigations of nuclear reaction mechanisms relevant to fusion physics and astrophysics. In this work, two-dimensional radiation hydrodynamic simulations based on the FLASH code are performed to investigate the plasma evolution and X-ray heating mechanisms of a foam target irradiated by a laser-driven hohlraum radiation source. The model incorporates a three-temperature (electron-ion-radiation) framework, multi-group radiation transport, laser energy deposition, and electron thermal conduction, enabling a self-consistent description of energy conversion and transport processes. The results show that, following laser energy deposition, the hohlraum establishes a quasi-blackbody radiation field with a radiation temperature of approximately 20 eV through multiple absorption and re-emission processes. For a low-density foam target (2 mg/cm³), this radiation field drives a supersonic radiation heat wave (with propagation velocity much higher than the local sound speed), resulting in volumetric energy deposition and near-isochoric heating. Within the time window of 4 ns < t < 8 ns, a highly uniform plasma channel with a width of about 260 μm is formed, where both areal density and electron temperature exhibit good spatiotemporal uniformity (average electron temperature ~17.9 eV, electron density ~4.1×10²⁰ cm^–3). This provides an optimal temporal and spatial window for ion beam transport and related measurements. With increasing foam density, the X-ray absorption becomes progressively localized near the surface, leading to a transition of the heating mechanism. Specifically, the dominant process evolves from supersonic radiation heat wave–driven volumetric heating to ablation-driven heating, accompanied by enhanced hydrodynamic motion and a significant increase in kinetic energy density. When the foam density reaches 10 mg/cm³, the kinetic energy becomes comparable to the internal energy, indicating the breakdown of the near-isochoric condition and the dominance of ablative processes. These results reveal the density-dependent transition of X-ray heating mechanisms in foam targets and clarify the underlying physical processes governing plasma uniformity and stability. This study provides important theoretical guidance for the experimental generation of quasi-static, spatially uniform plasmas and their application in ion beam transport and plasma nuclear reaction studies.