Spontaneous and external magnetic fields interacting with plasmas are essential in high-energy-density and magnetic confinement fusion physics. Measuring these magnetic fields, especially their topologies, is crucial. This paper develops a new type of optical polarimeter based on the Martin–Puplett interferometer (MPI), which can probe magnetic fields with the Faraday rotation method. We introduce the design and working principle of an MPI polarimeter. With the laboratory tests, we demonstrate the measurement process and compare the results with the measurement result of a Gauss meter. These very close results verify the polarization detection capability of the MPI polarimeter and show the potential for its application in magnetic field measurement.
Kelvin-Helmholtz instability is the basic physical process of fluids and plasmas. It is widely present in natural, astrophysical, and high energy density physical phenomena. With the construction of strong laser facilities, the research on high energy density physics has gained new impetus. However, in recent years the magnetized Kelvin-Helmholtz instability was rarely studied experimentally. In this work, we propose a new experimental scheme, in which a long-pulsed nanosecond laser beam is generated by a domestic starlight III laser facility. The whole target consists of two parts: the upper part that is the CH modulation layer with lower density, and the lower part that is the Al modulation layer with higher density. The laser beam is injected from one side of the CH modulation layer and generates a CH plasma outflow at the back of the target. During the transmission of the CH plasma outflow, the Al modulation layer is radiated and ionized, which makes the Al modulation layer generate an Al plasma outflow. The interaction between the Al plasma outflow and the CH plasma outflow produces a velocity shear layer, and then Kelvin-Helmholtz instability will gradually form near the Al modulation layer. In this paper, the open-source FLASH simulation program is used to conduct a two-dimensional numerical simulation of the Kelvin-Helmholtz instability generated by the laser-driven modulation target. We use the FLASH code, which is an adaptive mesh refinement program, developed by the Flash Center at the University of Chicago, and is well-known in astrophysics and space geophysics, to create a reference to the magnetohydrodynamic solution in our experiment. At present, this code introduces a complete high-energy-density physical modeling module, which is especially suitable for simulating intense laser ablation experiments. The equation of state and opacity tables of targets are based on the IONMIX4 database. The evolution of Kelvin-Helmholtz vortices, separately, in the Biermann self-generated magnetic field, the external magnetic field, and no magnetic field are investigated and compared with each other. It is found that the self-generated magnetic field hardly changes the morphology of the Kelvin-Helmholtz vortex during the evolution of Kelvin-Helmholtz instability. The external magnetic field parallel to the fluid direction can stabilize the shear flow. The magnetic field mainly stabilizes the long wave disturbance. The study results in this work can provide theoretical guidance for the next step of the Kelvin-Helmholtz experiment under a strong magnetic environment in the high energy density laser facility.
Rayleigh-Taylor instability (RTI) is a fundamental physical phenomenon in fluids and plasmas and plays a significant role in astrophysics, space physics, and engineering. Especially in inertial confinement fusion (ICF) research, numerous experimental and simulation results have identified RTI as one of the most significant barriers to achieving fusion. Understanding the origin and development of RTI will allow for formulating mitigation measures to curb the growth of instability, thereby improving the odds of ICF success. Although there have been many theoretical and experimental studies on RTI under high energy density, there are few experiments to systematically explore the influence of magnetic fields on the evolution of magnetized RTI. Here, a new experimental scheme is proposed based on the Shenguang-II laser facility which uses nanosecond laser beams to drive modulation targets of polystyrene (CH) and low-density foam layers. A shock wave is generated after the laser's CH modulation layer is ablated, propagates through CH to low-density foam, and causes Richtmyer-Meshkov instability when the shock wave accelerates the target. When the laser pulse ends, the shock wave evolves into a blast wave, causing the system to decelerate, resulting in RTI in the reference system of the interface. This paper uses the open-source radiation MHD simulation code (FLASH) to simulate the RTI generated by a laser-driven modulation target. The evolution of RTI without magnetic field, Biermann self-generated magnetic field, and different applied magnetic fields are systematically investigated and compared. The simulation results show that the Biermann self-generated magnetic field and the applied magnetic field in parallel flow direction do not change the interface dynamics in the evolution process of RTI. Nevertheless, the applied magnetic field in the vertical flow direction can stabilize RTI and the Kelvin-Helmholtz vortex at the tail of the RTI spike. Magnetic pressure plays a decisive role. The results provide a reference for the follow-up study of target physics related to ICF and deepen the understanding of the fluid mixing process.
Push and pull magnetic reconnection (MR) experiments using a high-power laser irradiating a capacitor target with the plates connected by a pair of coils are carried out. During the beginning (end) stages of the laser-target interaction that creates a hot plasma in the region, the rise (fall) of the coil currents generates expanding (contracting) magnetic fields that reconnect in the mid-plane between the coils, resulting in push (pull) MR. Proton radiography and proton ray-tracing simulation are used to track the evolution of the magnetic field distribution. The proton aggregate and void characteristics between the coils are related to the opposite current-sheet current during the push and pull MR stages. The directions of the hot plasma electron outflows during these two MR phases are obtained by monitoring the soft X-ray emission. Our results suggest that the double-coil capacitor target may be useful for laboratory modeling of fast MR and related phenomena in astrophysical plasmas.
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