Effect of plasma temperature on electrostatic shock generation and ion acceleration by laser

Abstract

The effect of plasma temperature on electrostatic shock generated by a circularly polarized laser pulse in overdense plasma is studied by particle-in-cell simulation. Ion reflection and transmission in the collisionless electrostatic shock (CES) are investigated analytically. As the initial ion temperature is varied, a distinct transition from the laser-driven piston scenario with all ions being reflected to the CES scenario with partial ion reflection is found. The results show that at low but finite temperatures the ions are much more accelerated than if they were cold.

Ultrafast collisional ion heating by electrostatic shocks

“…The spread in P x is larger and the number of protons reflected far less, in scenario a and d when the thermal dissipation mechanism is activated by the presence of the two ion species and the collisions between them. The greater number of protons passing through the shock is consistent with higher proton temperatures 31 . In contrast, panels b, c, e and f show the ion acceleration dissipation mechanism of CES clearly, with a double-layer structure and significant acceleration of protons.…”

“…Rapid heating of the ions proceeds via dynamical friction between the two species of ion. The higher temperature of the lighter ion species in the material with two different ion species causes a greater proportion of the lighter ion species to pass through the shock 31 , rather than be reflected, significantly changing the CES energy deposition into the target.…”

Ion acceleration by superintense laser-plasma interaction

“…The energies were actually higher than expected taking the vacuum laser intensity, suggesting that selffocusing in the underdense region could have increased the intensity in the plasma. We notice that Palmer et al (2011) reported on "protons accelerated by a radiation pressure driven shock", similarly to several authors who refer to HB or "piston" acceleration in thick targets as acceleration in the electrostatic shock sustained by the laser pressure at the front surface Zhang et al, 2009Zhang et al, , 2007b. In the context of ion acceleration by laser, we prefer to reserve the term "shock" for the regime described in Sec.IV.B which implies the generation of a "true" electrostatic shock wave, able to propagate into the plasma bulk and drive a ion acceleration there.…”

Enhanced ion acceleration in the ultra-intense laser driven magnetized collisionless shocks

“…Laser-driven ion acceleration is one of the most active research fields in the laser-plasma physics due to its advantage in accelerating ions to very high (multi-MeV) energies over sub-millimeter distances [1,2]. To date, several ion acceleration mechanisms have been proposed and observed experimentally, which include the target normal sheath acceleration [3][4][5][6][7], break-out afterburner [8][9][10][11], radiation pressure acceleration [12][13][14][15][16][17][18], collisionless shock acceleration (CSA) [19][20][21][22][23][24][25][26][27][28][29], etc. Recently, the CSA mechanism has attracted much attention due to its potential in generating monoenergetic ion beams in the μm-scale plasma targets, which is important for their applications in both science and medicine, such as the cancer therapy [30], proton radiography [31], and fast ignition inertial-confinement-fusion (ICF) [32].…”