van de Wetering J J, Hooker S M, Walczak R
John Adams Institute for Accelerator Science and Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, United Kingdom.
Somerville College, Woodstock Road, Oxford OX2 6HD, United Kingdom.
Phys Rev E. 2023 Jul;108(1-2):015204. doi: 10.1103/PhysRevE.108.015204.
We explore the regime of operation of the modulator stage of a recently proposed laser-plasma accelerator scheme [Phys. Rev. Lett. 127, 184801 (2021)0031-900710.1103/PhysRevLett.127.184801], dubbed the plasma-modulated plasma accelerator (P-MoPA). The P-MoPA scheme offers a potential route to high-repetition-rate, GeV-scale plasma accelerators driven by picosecond-duration laser pulses from, for example, kilohertz thin-disk lasers. The first stage of the P-MoPA scheme is a plasma modulator in which a long, high-energy "drive" pulse is spectrally modulated by copropagating in a plasma channel with the low-amplitude plasma wave driven by a short, low-energy "seed" pulse. The spectrally modulated drive pulse is converted to a train of short pulses, by introducing dispersion, which can resonantly drive a large wakefield in a subsequent accelerator stage with the same on-axis plasma density as the modulator. In this paper we derive the 3D analytic theory for the evolution of the drive pulse in the plasma modulator and show that the spectral modulation is independent of transverse coordinate, which is ideal for compression into a pulse train. We then identify a transverse mode instability (TMI), similar to the TMI observed in optical fiber lasers, which sets limits on the energy of the drive pulse for a given set of laser-plasma parameters. We compare this analytic theory with particle-in-cell (PIC) simulations and find that even higher energy drive pulses can be modulated than those demonstrated in the original proposal.
我们探索了一种最近提出的激光等离子体加速器方案[《物理评论快报》127, 184801 (2021)0031 - 900710.1103/PhysRevLett.127.184801]中调制器阶段的运行机制，该方案被称为等离子体调制等离子体加速器（P - MoPA）。P - MoPA方案为高重复率、GeV级的等离子体加速器提供了一条潜在途径，这种加速器由例如千赫兹薄盘激光器产生的皮秒级持续时间激光脉冲驱动。P - MoPA方案的第一阶段是一个等离子体调制器，其中一个长的高能“驱动”脉冲通过与由短的低能“种子”脉冲驱动的低振幅等离子体波在等离子体通道中共传播而进行光谱调制。通过引入色散，光谱调制后的驱动脉冲被转换为一系列短脉冲，这些短脉冲可以在后续具有与调制器相同轴上等离子体密度的加速器阶段中谐振驱动一个大的尾波场。在本文中，我们推导了等离子体调制器中驱动脉冲演化的三维解析理论，并表明光谱调制与横向坐标无关，这对于压缩成脉冲序列是理想的。然后，我们识别出一种横向模式不稳定性（TMI），类似于在光纤激光器中观察到的TMI，它为给定的一组激光 - 等离子体参数下的驱动脉冲能量设定了限制。我们将这种解析理论与粒子模拟（PIC）进行比较，发现可以调制的驱动脉冲能量甚至比原始提议中展示的还要高。
