Speaker
Description
Laser-driven ion acceleration in plasma is an active topic of research. Various acceleration mechanisms have been investigated. Recently, with the fast development of petawatt laser technology, laser ion acceleration in near-critical relativistically transparent (NCRT) plasma has attracted much attention. Nanomaterial targets offer one of the most promising approaches for generating NCRT plasma.
A petawatt laser pulse can make an initially over- but still near-critical plasma relativistically transparent and propagate in it. At the laser front, the laser radiation pressure piles up background electrons, generating a strong charge-separation field which is localized and comoving with the laser pulse. Basically, ion acceleration in the charge-separation field operates on principles analogous to electron acceleration in laser wakefield in dilute plasma [1,2].
However, as the plasma density increases, a new challenge arises. In dilute plasma, the laser plasma interaction mainly follows the linear dispersion relation and thus the phase velocity of the wakefield is dominated by the normalized plasma density. In a NCRT plasma, however, the laser-plasma interaction becomes highly nonlinear, and the propagation velocity of the laser-driven charge-separation field is governed by the balance between the electrostatic pressure and the laser radiation pressure, making it depend not only on the plasma density but also on the laser amplitude at the front [3,4]. This can result in an inertial force in the frame comoving with the charge-separation field, which can prevent the trapping of background ions or disrupt the acceleration of already trapped ions, especially when achieving high energy acceleration. In this talk we show that this can be overcome by employing a buffering underdense plasma to steepen the leading edge of the laser pulse in advance. This can lead to a superior ion acceleration process known as ion wave breaking acceleration [5] which is promising in producing quasi-mono-energetic and collimated ion beams.
[1] B. Liu, J. Meyer-ter-Vehn, and H. Ruhl, Physics of Plasmas 25, 103117 (2018).
[2] B. Liu, M. Shi, M. Zepf, B. Lei, and D. Seipt, Physical Review Letters 129, 274801 (2022).
[3] B. Liu, J. Meyer-ter-Vehn, H. Ruhl, and M. Zepf, Plasma Physics and Controlled Fusion 62, 085014 (2020).
[4] B. Liu, B. Lei, Y. Gao, M. Wen, K. Zhu, Plasma Physics and Controlled Fusion 66, 115004 (2024).
[5] B. Liu, J. Meyer-ter-Vehn, K.-U. Bamberg, W. J. Ma, J. Liu, X. T. He, X. Q. Yan, and H. Ruhl, Physical Review Accelerators and Beams 19, 073401 (2016).
