Peñano J R, Hafizi B, Sprangle P, Hubbard R F, Ting A
Plasma Physics Division, Beam Physics Branch, Naval Research Laboratory, Washington, D.C. 20375, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2002 Sep;66(3 Pt 2B):036402. doi: 10.1103/PhysRevE.66.036402. Epub 2002 Sep 17.
The propagation of intense laser pulses with durations longer than the plasma period through tapered plasma channels is investigated theoretically and numerically. General propagation equations are presented and reduced partial differential equations that separately describe the forward Raman (FR) and self-modulation (SM) instabilities in a nonuniform plasma are derived. Local dispersion relations for FR and SM instabilities are used to analyze the detuning process arising from a longitudinal density gradient. Full-scale numerical fluid simulations indicate parameters that favorably excite either the FR or SM instability. The suppression of the FR instability and the enhancement of the SM instability in a tapered channel in which the density increases longitudinally is demonstrated. For a pulse undergoing a self-modulation instability, calculations show that the phase velocity of the wakefield in an untapered channel can be significantly slower than the pulse group velocity. Simulations indicate that this wake slippage can be forestalled through the use of a tapered channel.
研究了持续时间长于等离子体周期的强激光脉冲在锥形等离子体通道中的传播，进行了理论和数值研究。给出了一般传播方程，并推导了分别描述非均匀等离子体中前向拉曼（FR）和自调制（SM）不稳定性的简化偏微分方程。利用FR和SM不稳定性的局部色散关系分析了纵向密度梯度引起的失谐过程。全尺度数值流体模拟表明了有利于激发FR或SM不稳定性的参数。证明了在纵向密度增加的锥形通道中，FR不稳定性受到抑制，SM不稳定性得到增强。对于经历自调制不稳定性的脉冲，计算表明，在无锥度通道中尾波场的相速度可能明显慢于脉冲群速度。模拟表明，通过使用锥形通道可以防止这种尾波滑移。
