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Liu, Chuan-Sheng

Publications and source records attributed to Liu, Chuan-Sheng.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Inhibition of stimulated Raman scattering due to the excitation of stimulated Brillouin scattering

The nonlinear coupling between stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) of intense laser in underdense plasma is studied theoretically and numerically. Based upon the fluid model, their coupling equations are derived, and a threshold condition of plasma density perturbations due to SBS for the inhibition of SRS is given. Particle-in-cell simulations show that this condition can be achieved easily by SBS in the so-called fluid regime with kLλD<0.15, where kL is the Langmuir wave number and λD is the Debye length [Kline et al., Phys. Plasmas 13, 055906 (2006)]. SBS can reduce the saturation level of SRS and the temperature of electrons in both homogeneous and inhomogeneous plasma. Numerical simulations also show that this reduced SRS saturation is retained even if the fluid regime condition mentioned above is violated at a later time due to plasma heating.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Effects of large laser bandwidth on stimulated Raman scattering instability in underdense plasma

The effects of laser bandwidth on stimulated Raman scattering (SRS) instability in underdense plasma are studied by particle-in-cell simulations. In the simulations, sinusoidal frequency modulation of the incident laser pulse is used. By changing the size of bandwidth, it is shown that the linear growth of SRS can be suppressed considerably, provided the laser bandwidth is much larger than the SRS linear growth rate. Simulations also show that by choosing the proper frequency modulation parameters or decreasing the linear growth rate of SRS, the inhibitory effects become more obvious. The plasma electron temperature tends to weaken the bandwidth effects especially when it is over a keV level. The laser bandwidth can only increase the time duration for linear growth but cannot diminish the instability completely.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Spot size dependence of laser accelerated protons in thin multi-ion foils

We present a numerical study of the effect of the laser spot size of a circularly polarized laser beam on the energy of quasi-monoenergetic protons in laser proton acceleration using a thin carbon-hydrogen foil. The used proton acceleration scheme is a combination of laser radiation pressure and shielded Coulomb repulsion due to the carbon ions. We observe that the spot size plays a crucial role in determining the net charge of the electron-shielded carbon ion foil and consequently the efficiency of proton acceleration. Using a laser pulse with fixed input energy and pulse length impinging on a carbon-hydrogen foil, a laser beam with smaller spot sizes can generate higher energy but fewer quasi-monoenergetic protons. We studied the scaling of the proton energy with respect to the laser spot size and obtained an optimal spot size for maximum proton energy flux. Using the optimal spot size, we can generate an 80 MeV quasi-monoenergetic proton beam containing more than 10{sup 8} protons using a laser beam with power 250 TW and energy 10 J and a target of thickness 0.15 wavelength and 49 critical density made of 90% carbon and 10% hydrogen.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Enhancement of proton energy by polarization switch in laser acceleration of multi-ion foils

We present a scheme to significantly increase the energy of quasi-monoenergetic protons accelerated by a laser beam without increasing the input power. This improvement is accomplished by first irradiating the foil several wave periods with circular polarization and then switching the laser to linear polarization. The polarization switch increases the electron temperature and thereby moves more electrons ahead of the proton layer, resulting in a space charge electric field pushing the protons forwards. The scaling of the proton energy evolution with respect to the switching time is studied, and an optimal switching time is obtained. The proton energy for the case with optimal switching time can reach about 80 MeV with an input laser power of 70 TW, an improvement of more than 30% compared to the case without polarization switch.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Three dimensional effects on proton acceleration by intense laser solid target interaction

Multi-dimensional effects on ion acceleration by a normally incident linearly polarized intense laser pulse interacting with a thin solid target have been investigated numerically, where the laser has the peak intensity of 1.37×10{sup 20} W/cm{sup 2}, focused spot size of 6 μm, pulse duration of 33 fs, and total pulse energy about 3 J, which are commercially available now. We have checked the effects of simulation geometries by running one, two, and three dimensional (1D, 2D, 3D) particle-in-cell simulations. 3D simulation results show that, in the case of using a relatively thick target (in the opaque regime, i.e., 2 μm) with the so-called target normal sheath field acceleration mechanism, electrons spread almost uniformly along two transverse directions. While in the case of using an ultra-thin target (in the relativistic-induced transparent regime, i.e., 100 nm) with the so-called break-out afterburner mechanism, electrons spread more quickly along the direction orthogonal to the laser polarization direction especially at the early stage. The transverse spreading of electrons strongly decreases the electron density at the rear side of the target. Such an effect causes different estimation of electron temperatures in different simulation geometries. Usually, 1D and 2D simulations overestimate the temperature; and as a result, the maximum proton energy observed in 1D and 2D simulations is, respectively, about 3 and 2 times of that observed in 3D simulation.

43 PARTICLE ACCELERATORS↗