Ion shock acceleration by large amplitude slow ion acoustic double layers in laser-produced plasmas

Abstract

A kinetic model for the shock acceleration of ions in laser-produced plasmas is developed. A fraction of the warm ions are accelerated by the large amplitude monotonic potential of the shock created due the plasma compression and electron heating by the laser. The kinetic model for the monotonic shock is based on the slow ion acoustic double layer (SIADL). It is found that the amplitude of the large amplitude SIADL is almost uniquely defined by the electron temperature. Therefore, a balance between electron heating and plasma compression is needed for optimal ion acceleration by this scheme. Typical Mach numbers of the monotonic shocks are close to 1.5. The scheme could potentially produce monoenergetic ions with a relative energy spread of less than 1%. The model is compared with recent simulations and experiments, where efficient shocks acceleration and production of monoenergetic protons have been observed. Similarities and differences with other shock models are pointed out and discussed

Improving the quality of proton beams via double targets driven by an intense circularly polarized laser pulse

“…6 Among them, ion acceleration via laser-driven plasmas has become a hot research topic in recent years [7][8][9] due to its potential applications in fields like proton radiography, 10 hadron therapy, 11 particle physics 12 and fusion ignitions 13 etc. Till now, lots of acceleration mechanisms have been proposed, such as the plasma wake field acceleration, 14 the target normal sheath acceleration (TNSA), [15][16][17][18] shock-wave acceleration at the front of the target, 19,20 and radiation pressure acceleration (RPA). 21,22 Although the maximum energy an ion can obtain from the laser pulse is proportional to the intensity of laser pulse and the cube root of acceleration time or distance theoretically, 23,24 yet the focused peak intensity of laser is always limited by the material breakdown threshold in practice, 25 and many other undesirable effects such as instabilities come to appear over long interaction time.…”

Particle-in-cell simulation study of a lower-hybrid shock

“…Self-consistent and steady-state solutions of an ion acoustic wave that steepened into an electrostatic shock exist, provided that the speed of the upstream plasma measured in the shock frame does not exceed a few times the ion acoustic speed. 8 Electrostatic shocks are now routinely produced in laser-plasma experiments [11][12][13][14][15][16][17][18] and they attract considerable interest because they allow us to study in-situ some of the plasma processes that develop in remote astrophysical environments. For example, the shocks that ensheath the blast shells of supernova remnants.…”

“…The ion acoustic wave is the only wave mode in a nonrelativistic setting and in the absence of a background magnetic field, which can modulate the density of the ions. It is thus the only wave mode that can sustain an electrostatic shock [1][2][3][4][5][6][7][8] in a collisionless unmagnetized plasma unless the collision speed is high enough to yield a partially magnetic shock [9,10]. The density gradient at the electrostatic shock drives an ambipolar electric field, which puts the downstream region behind the shock on a higher positive potential than the upstream region ahead of it.…”

“…The therefrom resulting compression of the plasma sustains the density gradient. Self-consistent and steady-state solutions of an ion acoustic wave that steepened into an electrostatic shock exist, provided that the speed of the upstream plasma measured in the shock frame does not exceed a few times the ion acoustic speed [8].…”

Laser acceleration of protons using multi-ion plasma gaseous targets

“…In this paper, we demonstrate by two-dimensional (2D) particle-in-cell (PIC) simulation that a quasimonoenergetic proton beam can be obtained using a long acceleration time, where the signatures of RPA, SCR, TNSA, and shock acceleration [38,39] can all be observed. We discuss advantages and disadvantages with different target thicknesses and densities, and then finally compare the proton energy evolution between the simulation results and our theoretical model and show that RPA and SCR are two main effects in the acceleration process.…”