We report on the experimental investigation of magnetic field generation with a half-loop gold sheet coil driven by long-duration (10 ns) and high-power (0.5 TW) laser pulses. The amplitude of the magnetic field was characterized experimentally using proton deflectometry. The field rises rapidly in the first 1 ns of laser irradiation, and then increases slowly and continuously up to 10 ns during further laser irradiation. The transient dynamics of current shape were investigated with a two-dimensional (2D) numerical simulation that included Ohmic heating of the coil and the resultant change of electrical resistivity determined by the coil material temperature. The numerical simulations show rapid heating at the coil edges by current initially localized at the edges. This current density then diffuses to the central part of the sheet coil in a way that depends both on normal current diffusion as well as temporal changes of the coil resistance induced by the Ohmic heating. The measured temporal evolution of the magnetic field is compared with a model that determines a solution to the coil current and voltage that is consistent with a plasma diode model of the drive region and a 2D simulation of current diffusion and dynamic resistance due to Ohmic heating in the laser coil.

中文翻译：

---

使用长激光脉冲产生激光的磁场的动力学

我们报告了由长周期（10 ns）和高功率（0.5 TW）激光脉冲驱动的半环金片线圈产生磁场的实验研究。磁场的振幅通过质子偏折法进行了实验表征。在最初的1 ns激光辐照中，该场迅速上升，然后在进一步的激光辐照期间缓慢且连续地增长，直至10 ns。通过二维（2D）数值模拟研究了电流形状的瞬态动力学，其中包括线圈的欧姆加热以及由线圈材料温度决定的电阻率变化。数值模拟表明，线圈的边缘被最初定位在边缘的电流快速加热。然后，该电流密度以既取决于正常电流扩散又取决于欧姆加热引起的线圈电阻随时间变化的方式扩散到薄板线圈的中央部分。将测得的磁场随时间变化的模型与确定线圈电流和电压的解决方案的模型进行比较，该模型与驱动区域的等离子二极管模型以及由于欧姆加热引起的电流扩散和动态电阻的2D模拟一致激光线圈。