Fast electron energy deposition in aluminium foils: Resistive vs. drag heating
Fast electron energy deposition in aluminium foils: Resistive vs. drag heating
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铝箔中的快速电子能量沉积：电阻加热与拖动加热
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发表时间：
2009
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通讯作者：
J. Honrubia
中科院分区：
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作者：
J. Santos;A. Debayle;P. Nicolaï;V. Tikhonchuk;M. Manclossi;D. Batani;A. Guemnie;J. Faure;V. Malka;J. Honrubia
用0.7J、40 fs、61019 Wcm ~（-2）激光脉冲与10-200 μm厚铝箔相互作用，研究了强流电子束的束流损耗。快电子束特性和箔温度是通过记录在光域中的两个不同波长处（λ 407 nm（激光的二次谐波）和λ 500 nm）来自箔后侧的电磁发射的强度来测量的。实验观察到的快速电子分布包含两个组成部分：一条相对论性的尾巴，（Thtail ~ 10 MeV）和高度准直（7° ± 3°）电子，携带少量能量（不到1%的激光能量），另一个，加速电子的大部分，包含较低的能量（Thbulk=500 ± 100 keV）更多的发散电子（35 ± 5°），其传输约35%的激光能量。相对论分量表现为由于相互作用区中电子密度的调制而产生的相干2ω0发射。大部分成分引起强烈的目标加热，从箔后侧产生可测量的热发射产率。我们的数据和建模表明，两种机制的快速电子能量沉积：电阻加热由于中和返回电流和碰撞的快速电子与等离子体电子。电阻机制在浅靶深度处更为重要，代表在15 μm处每焦耳激光能量100 eV的加热速率。超过该深度，由于光束发散，入射电流低于1012 Acm-2，碰撞加热变得比电阻加热更重要。在50 μm深度处的加热速率仅为1.5eV/J。
The high current electron beam losses have been studied experimentally with 0.7 J, 40 fs, 6 1019 Wcm-2 laser pulses interacting with Al foils of thicknesses 10-200 μm. The fast electron beam characteristics and the foil temperature were measured by recording the intensity of the electromagnetic emission from the foils rear side at two different wavelengths in the optical domain, ≈407 nm (the second harmonic of the laser light) and ≈500 nm. The experimentally observed fast electron distribution contains two components: one relativistic tail made of very energetic (Thtail ≈ 10 MeV) and highly collimated (7° ± 3°) electrons, carrying a small amount of energy (less than 1% of the laser energy), and another, the bulk of the accelerated electrons, containing lower-energy (Thbulk=500 ± 100 keV) more divergent electrons (35 ± 5°), which transports about 35% of the laser energy. The relativistic component manifests itself by the coherent 2ω0 emission due to the modulation of the electron density in the interaction zone. The bulk component induces a strong target heating producing measurable yields of thermal emission from the foils rear side. Our data and modeling demonstrate two mechanisms of fast electron energy deposition: resistive heating due to the neutralizing return current and collisions of fast electrons with plasma electrons. The resistive mechanism is more important at shallow target depths, representing an heating rate of 100 eV per Joule of laser energy at 15 μm. Beyond that depth, because of the beam divergence, the incident current goes under 1012 Acm-2 and the collisional heating becomes more important than the resistive heating. The heating rate is of only 1.5 eV per Joule at 50 μm depth.