Preplasma effects on the generation of high-energy protons in ultraintense laser interaction with foil targets

Abstract

It is shown that the intense quasistatic electric and magnetic fields self-generated near the axis of the laser-driven channel in an appropriately profiled preplasma during ultraintense laser interaction with a thin target can create dense relativistic electron bunches. The latter easily penetrate through the target and can greatly enhance the sheath field at the rear, resulting in significant increase in the laser-to-ion energy conversion efficiency and the maximum energy of the target normal sheath accelerated ions. Particle-in-cell simulations show that with a hydrogen targets a proton beam of peak energy ∼38 MeV and energy conversion efficiency ≥6.5% can be produced by a linearly polarized 5 × 1019 W/cm2 laser. An analytical model is also proposed and its results agree well with those of the simulations.

Laser-Driven Ion Acceleration from Plasma Micro-Channel Targets

“…In the past decade, a large amount of efforts have been dedicated to the research into the boost of ion beam energies, such as using undersense or near-critical density plasmas 19 20 45 , porous-structured-films 21 22 23 , and micro-tubes 25 26 . Most of these schemes are based on the improvement of the hot electron temperature.…”

“…For a simple planar target, J × B heating 16 or vacuum heating 17 dominates the hot-electron generation, while the obtained hot-electrons are usually k B T h < eϕ p and n h < n c , in which k B is the Boltzmann constant, eϕ p is the ponderomotive potential and n c is the critical plasma density 18 . Many methods such as placing suitable-scale preplasma 19 20 and employing nanosphere surface 21 22 23 or microcone 24 25 has been suggested to heat the electrons. Nevertheless, simultaneously great increase of n h and T h remains a challenging endeavor.…”

Laser-plasma proton acceleration with a combined gas-foil target

“…These include coating the foil with foams [2][3][4][5][6], nanospheres [7], micropillar arrays [8], microchannels [9] and even bacteria [10]. In another approach, the foil is pre-irradiated by a weaker pulse, creating a plasma density gradient which can be controlled by the delay between the main and pre-pulse [11][12][13][14][15][16][17][18][19][20]. These methods exhibit improved performance mainly due to enhanced laser absorption in the first near-critical density layer which eventually translates into higher ion energies.…”

Target normal sheath acceleration of protons using triple-layer target with long preplasma

“…In the presence of preplasma generated by the laser prepulse, the electrons in the preplasma are also accelerated and heated by the main laser pulse and can easily propagate through the target and enter the backside vacuum [23][24][25][26][27]. Similarly, a low-density or foam layer in front of the main target layer can enhance the density and energy of the hot electrons producing the sheath field behind the target [5,[28][29][30].…”