Generation Of Heavy Ion Beams Research Articles

Generation of heavy ion beams using femtosecond laser pulses in the target normal sheath acceleration and radiation pressure acceleration regimes

Theoretical study of heavy ion acceleration from sub-micron gold foils irradiated by a short pulse laser is presented. Using two dimensional particle-in-cell simulations, the time history of the laser pulse is examined in order to get insight into the laser energy deposition and ion acceleration process. For laser pulses with intensity 3×1021 W/cm2, duration 32 fs, focal spot size 5 μm, and energy 27 J, the calculated reflection, transmission, and coupling coefficients from a 20 nm foil are 80%, 5%, and 15%, respectively. The conversion efficiency into gold ions is 8%. Two highly collimated counter-propagating ion beams have been identified. The forward accelerated gold ions have average and maximum charge-to-mass ratio of 0.25 and 0.3, respectively, maximum normalized energy 25 MeV/nucleon, and flux 2×1011 ions/sr. An analytical model was used to determine a range of foil thicknesses suitable for acceleration of gold ions in the radiation pressure acceleration regime and the onset of the target normal sheath acceleration regime. The numerical simulations and analytical model point to at least four technical challenges hindering the heavy ion acceleration: low charge-to-mass ratio, limited number of ions amenable to acceleration, delayed acceleration, and high reflectivity of the plasma. Finally, a regime suitable for heavy ion acceleration has been identified in an alternative approach by analyzing the energy absorption and distribution among participating species and scaling of conversion efficiency, maximum energy, and flux with laser intensity.

The radiation reaction effects in the ultra-intense and ultra-short laser foil interaction regime

The extreme laser intensity, IL>1023 W/cm2, will be made possible by Extreme Light Infrastructure. Such an ultra-intense and ultra-short laser pulse promises to promote laser-matter interaction into the exotic quantum-electro-dynamical regime. Electrons quivering in such a strong laser pulse experience a radiation reaction (RR) friction force by radiating high frequency photons. These extreme intensities will also make possible acceleration of heavy ions in new regimes. In this paper, the heavy ion beam generation based on ultra-intense and ultra-short laser foil interaction is systematically studied. Three-dimensional particle-in-cell simulations which include an energy conserving electrodynamics model for RR force and the corresponding γ-photons emission have been used. The energy partition into electrons, ions, and photons has been investigated in relation to efficient generation of heavy ion beams by linearly and circularly polarized (LP and CP) laser and for different foil thicknesses. It is found that the CP and LP cases each have an optimal foil thickness for efficient ion beam generation; the RR force has a stronger effect upon laser coupling to an opaque foil target for an LP laser than a CP laser; and the emitted photons are proven to be an efficient source of γ-ray emission with the peak frequency as high as 106∼108 times the laser frequency.

Laser Accelerated, High Quality Ion Beams

Intense beams of protons and heavy ions have been observed in ultra-intense laser-solid interaction experiments. Thereby, a considerable fraction of the laser energy is transferred to collimated beams of energetic ions (e.g. up to 50 MeV protons; 100 MeV fluorine), which makes these beams highly interesting for various applications. Experimental results indicate very short pulse duration and an excellent beam quality, leading to beam intensities in the TW range. To characterize the beam quality and its dependence on laser parameters and target conditions we performed experiments at several high-power laser systems. We found a strong dependence on the target rear surface conditions allowing to tailor the ion beam by an appropriate target design. We also succeeded in the generation of heavy ion beams by suppressing the proton amount at the target surface.

The generation of high-quality, intense ion beams by ultra-intense lasers

Intense beams of protons and heavy ions have been observed in ultra-intense laser–solid interaction experiments. Thereby, a considerable fraction of the laser energy is transferred to collimated beams of energetic ions (e.g. up to 50 MeV protons; 100 MeV fluorine), which makes these beams highly interesting for various applications. Experimental results indicate a very short-pulse duration and an excellent beam quality, leading to beam intensities in the TW range. To characterize the beam quality and its dependence on laser parameters and target conditions we performed experiments using the 100 TW laser system at Laboratoire pour l'Utilisation des Lasers Intenses at the Ecole Polytechnique, France, with focused intensities exceeding 1019 W cm−2. We found a strong dependence on the target rear surface conditions allowing to tailor the ion beam by an appropriate target design. We also succeeded in the generation of heavy ion beams by suppressing the proton amount at the target surface. We will present recent experimental results demonstrating a transverse beam emittance far superior to the accelerator based ion beams. Finally, we will discuss the prospect of laser accelerated ion beams as new diagnostics in laser–solid interaction experiments. Special fields of interest are proton radiography, electric field imaging, and relativistic electron transport inside the target.

Low energy ion modification of thin films

This paper presents some of the uses of broad beams of low energy (< 500 eV) ions for modifying surfaces and thin films physically and chemically. We discuss bombardment-induced variation in the index of refraction of thin films with applications in integrated optics, variation of etch profiles using biased masks, and generation of heavy ion beams. ZrO x F y films were made by depositing ZrF 4 with a coincident oxygen ion flux. The index of refraction can be increased by 0.12 without increasing waveguide losses beyond 8 dB/cm, with ion energy being the primary determinant of index variation, and ion flux having the largest effect on losses. The second modification technique focuses on the use of local fields at the substrate to alter the path of incoming ions. Using voltage biased metal masks, we have been able to alter the sputter-etch profile of thin films. The experimental results are compared with calculated etch profiles; changes in the etch angle of up to 20° have been observed. We describe preliminary work on the generation and use of C 60 and metal ions as bombarding particles.