Heavy ion beams generated by conventional RF-driven accelerators are commonly used in nuclear and particle physics. They have also found application in materials research, high energy-density physics and other domains. Heavy ion beams can also be generated by laser-driven ion accelerators, which are considered to be a promising alternative or supplement to RF-driven accelerators. However, to produce in these accelerators ion beams with the GeV or multi-GeV ion energies desired in most applications, multi-PW short-pulse laser drivers and ultra-relativistic laser intensities (~ 1023 W/cm2 or higher) are required. Multi-PW lasers capable of producing femtosecond pulses with ultra-relativistic intensities are currently being built, in particular, as part of the pan-European Extreme Light Infrastructure (ELI) project. The acceleration of heavy ions at ultra-relativistic laser intensities is, however, a poorly explored research field and requires extensive and detailed studies. In this paper, the results of numerical investigations of the acceleration of heavy (Pb) ions from a thin (0.1 um) lead target irradiated by a circularly polarized 30-fs, multi-PW laser pulse with intensity of 1023 W/cm2 are presented. The numerical simulations were performed using fully electromagnetic, multi-dimensional (2D3V) particle-in-cell code PICDOM, which includes, in particular, the dynamic ionization of the irradiated target and the accelerated ions. It was found that although the ion beam accelerated by the laser pulse contains more than 50 ion species with the charge state z ranging from z = 25 to z = 80, almost all of the energy of the beam (over 90% of the beam energy) is accumulated in ions with z = 72. Among all the accelerated ions, these ions have the highest both mean and peak energy, which values reach 14,6 GeV and 70,4 GeV, respectively. At a small distance from the target (<50 um), the intensity of the ion beam with z = 72 exceeds 1020 W/cm2 , and the duration of the ion pulse lies in the sub-picosecond range. Such intensities and durations of heavy ion beams are unachievable in currently operating RF-driven accelerators. The demonstrated laserdriven ion beams can thus open the door to new areas of research and applications not available for conventional accelerators.
The Extreme Light Infrastructure (ELI) is a large-scale pan-European project currently being implemented in three European countries. It uses cutting-edge laser technologies to build multi-PW lasers capable of generating femtosecond light pulses of ultra-relativistic intensities (~ 1023 – 1024 W/cm2 ), unattainable so far. Such light pulses can accelerate ions to high energies and produce collimated ion beams with unique features that have the potential to be applied in various fields of scientific research, as well as in technological and medical developments. In this paper, the results of numerical studies on the acceleration of heavy (thorium) ions driven by a femtosecond multi-PW laser pulse of ultrarelativistic intensity, performed with the use of a multi-dimensional (2D3V) particle-in cell code, are presented. It is shown that ultra-intense sub-picosecond multi-GeV heavy ion beams with a beam intensity much higher (by a factor of ~ 102 ) and with ion pulse durations much shorter (by a factor of ~ 104 ) than presently achievable in conventional RFdriven accelerators can be produced at laser intensities of 1023 W/cm2 predicted for the ELI lasers. Such ion beams can open the door to new areas of research in nuclear and high energy-density physics, and possibly in other scientific domains.
The paper reports the results of two-dimensional particle-in-cell simulations of proton beam acceleration at the interactions of a 130-fs laser pulse of intensity from the range of 1021 – 1023 W/cm2, predicted for the Extreme Light Infrastructure (ELI) lasers currently built in Europe, with a thin hydrocarbon (CH) target. A special attention is paid to the effect of the laser pulse intensity and polarization (linear - LP, circular - CP) as well as the target thickness on the proton energy spectrum, the proton beam spatial distribution and the proton pulse shape and intensity. It is shown that for the highest, ultra-relativistic intensities (~ 1023 W/cm2) the effect of laser polarization on the proton beam parameters is relatively weak and for both polarizations quasi-monoenergetic proton beams of the mean proton energy ~ 2 GeV and δE/E ≈ 0.3 for LP and δE/E ≈ 0.2 for CP are generated from the 0.1-μm CH target. At short distances from the irradiated target (< 50 um), the proton pulse is very short (< 20 fs), and the proton beam intensities reach extremely high values > 1021 W/cm2, which are much higher than those attainable in conventional accelerators. Such proton beams can open the door for new areas of research in high energy-density physics and nuclear physics as well as can also prove useful for applications in materials research e.g. as a tool for high-resolution proton radiography.
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