Study of photo-transmutation induced by laser wakefield accelerated electrons
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摘要: 提出了一种基于激光尾波场加速电子诱导光核嬗变的优化方案并开展了135Cs光核嬗变的数值模拟研究。蒙特卡罗模拟研究发现随着电子能量的增加，嬗变产额逐渐趋于饱和，单位能量电子的嬗变效率在40 MeV附近时存在峰值，半高处能量为20、120 MeV。为了提升半高处能量内的电子电量从而优化嬗变产额，使用粒子模拟程序研究了超短超强激光在气体等离子体中的传输过程。研究结果发现，随着等离子体密度的降低，尾波场加速的电子能量逐渐升高，但是电荷量逐渐减少，并且圆偏振激光加速的电子能量和电荷量均优于线偏振激光。通过调整等离子体密度和激光偏振，发现在圆偏振激光和特定等离子体密度条件下，存在嬗变产额的最优值。利用电导率等效方法对345 GHz折叠波导行波管中的电磁信号的传输损耗进行了仿真研究，考察了流通管孔径、加工粗糙度等对冷腔传输损耗的影响，流通管孔径较大或加工粗糙度较大都会导致电磁信号传输衰减严重。还模拟分析了热腔中电磁信号衰减对慢波结构净增益、带宽、最佳周期数等器件特征参数的影响，结果显示，电磁信号衰减会使得增益下降和带宽降低。Abstract: Photo-transmutation is an important path to handle long-lived fission products. In this research work, an optimization scheme of photo-transmutation induced by Laser WakeField Acceleration (LWFA) driven electrons is proposed. Numerical simulations of photo-transmutation of 135Cs by this scheme are performed. Monte Carlo simulations show that with increasing electron energy, transmutation yield gradually saturates. The transmutation efficiency per unit electron energy has a peak near 40 MeV, with half-maximum energy of 20−120 MeV. To enhance electron charge within the half-maximum energy range and optimize transmutation yield, PIC simulation was used to study the transmission process of ultrashort and ultra-intense lasers in gas plasma. The results show that as plasma density decrease, the energy of electrons gradually increase while their charge are gradually reduced. Moreover, circularly polarized lasers exhibit higher electron energy and charge than linearly polarized ones. Through adjusting the plasma density and laser polarization, it is found that there is an optimal value for transmutation yield under the conditions of circular polarization and specific density. The scheme is expected to promote the studies of nuclide transmutation in a tabletop ultra-intense and ultra-short laser device with high repetition rate, as well as the potential applications in medicine and nuclear-waste management.
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图 2 嬗变靶厚度为3 mm，6 mm，10 mm时不同电子能量的嬗变产额与嬗变效率
Figure 2. Transmutation yield and transmutation efficiency of different electron energy at the target thickness of 3 mm, 6 mm and 10 mm
图 3 线偏振激光与不同密度气体作用的电子加速图像
Figure 3. Electron acceleration images of linearly polarized laser acting with gas of different densities
图 4 线偏振激光与不同密度气体作用产生的电子能谱
Figure 4. Electron energy spectrum generated by the action of linearly polarized laser with gas of different densities
图 5 不同偏振激光与气体作用产生的准静态轴向磁场
Figure 5. Quasistatic axial magnetic field generated by the interaction of different polarization laser light and gas
图 6 圆偏振激光与不同密度气体作用产生的电子能谱和总电荷量
Figure 6. Electron energy spectrum and total charge generated by the action of circularly polarized laser with different densities
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