Scaling laws for energetic ions from the commissioning of the new Los Alamos National Laboratory 200 TW Trident laser

Analysis of laser-proton acceleration experiments for development of empirical scaling laws

Numerous experiments on laser-driven proton acceleration in the MeV range have been performed with a large variety of laser parameters since its discovery around the year 2000. Both experiments and simulations have revealed that protons are accelerated up to a maximum cut-off energy during this process. Several attempts have been made to find a universal model for laser proton acceleration in the target normal sheath acceleration regime. While these models can qualitatively explain most experimental findings, they can hardly be used as predictive models, for example, for the energy cut-off of accelerated protons, as many of the underlying parameters are often unknown. Here we analyze experiments on laser proton acceleration in which scans of laser and target parameters were performed. We derive empirical scaling laws from these parameter scans and combine them in a scaling law for the proton energy cut-off that incorporates the laser pulse energy, the laser pulse duration, the focal spot radius, and the target thickness. Using these scaling laws, we give examples for predicting the proton energy cut-off and conversion efficiency for state-of-the-art laser systems.

Laser-accelerated particle beams for stress testing of materials

Laser-driven particle acceleration, obtained by irradiation of a solid target using an ultra-intense (I > 10¹⁸ W/cm²) short-pulse (duration <1 ps) laser, is a growing field of interest, in particular for its manifold potential applications in different domains. Here, we provide experimental evidence that laser-generated particles, in particular protons, can be used for stress testing materials and are particularly suited for identifying materials to be used in harsh conditions. We show that these laser-generated protons can produce, in a very short time scale, a strong mechanical and thermal damage, that, given the short irradiation time, does not allow for recovery of the material. We confirm this by analyzing changes in the mechanical, optical, electrical, and morphological properties of five materials of interest to be used in harsh conditions.

Recently, there has been significant progress on the application of laser-generated proton beams in material science. Here the authors demonstrate the benefit of employing such beams in stress testing different materials by examining their mechanical, optical, electrical, and morphological properties.

RADIOLOGICAL SAFETY ASSESSMENT FOR THE EXPERIMENTAL AREA OF A HYPER-INTENSE LASER WITH PEAK-POWER OF 1PW-CETAL

Ultra-high intensity lasers in use are connected with ionizing radiation sources that raise a real concern in relation to installations, personnel, population and environment protection. The shielding of target areas in these facilities has to be evaluated from the conceptual stage of the building design. The sizing of the protective concrete walls was determined using computer codes such as Fluka. For the experiments to be carried out in the facility of the Center for Advanced Laser Technologies (CETAL), both proton beams with the energy of 100 MeV and electron beams with 300 MeV energy were considered to calculate the dimensions of structural shielding and to establish technical solutions fulfilling the radiation protection constraints imposed by the National Commission for Nuclear Activities Control.

Relativistically induced transparency acceleration of light ions by an ultrashort laser pulse interacting with a heavy-ion-plasma density gradient

The relativistically induced transparency acceleration (RITA) scheme of proton and ion acceleration using laser-plasma interactions is introduced, modeled, and compared to the existing schemes. Protons are accelerated with femtosecond relativistic pulses to produce quasimonoenergetic bunches with controllable peak energy. The RITA scheme works by a relativistic laser inducing transparency [Akhiezer and Polovin, Zh. Eksp. Teor. Fiz 30, 915 (1956); Kaw and Dawson, Phys. Fluids 13, 472 (1970); Max and Perkins, Phys. Rev. Lett. 27, 1342 (1971)] to densities higher than the cold-electron critical density, while the background heavy ions are stationary. The rising laser pulse creates a traveling acceleration structure at the relativistic critical density by ponderomotively [Lindl and Kaw, Phys. Fluids 14, 371 (1971); Silva et al., Phys. Rev. E 59, 2273 (1999)] driving a local electron density inflation, creating an electron snowplow and a co-propagating electrostatic potential. The snowplow advances with a velocity determined by the rate of the rise of the laser's intensity envelope and the heavy-ion-plasma density gradient scale length. The rising laser is incrementally rendered transparent to higher densities such that the relativistic-electron plasma frequency is resonant with the laser frequency. In the snowplow frame, trace density protons reflect off the electrostatic potential and get snowplowed, while the heavier background ions are relatively unperturbed. Quasimonoenergetic bunches of velocity equal to twice the snowplow velocity can be obtained and tuned by controlling the snowplow velocity using laser-plasma parameters. An analytical model for the proton energy as a function of laser intensity, rise time, and plasma density gradient is developed and compared to 1D and 2D PIC OSIRIS [Fonseca et al., Lect. Note Comput. Sci. 2331, 342 (2002)] simulations. We model the acceleration of protons to GeV energies with tens-of-femtoseconds laser pulses of a few petawatts. The scaling of proton energy with laser power compares favorably to other mechanisms for ultrashort pulses [Schreiber et al., Phys. Rev. Lett. 97, 045005 (2006); Esirkepov et al., Phys. Rev. Lett. 92, 175003 (2004); Silva et al., Phys. Rev. Lett. 92, 015002 (2004); Fiuza et al., Phys. Rev. Lett. 109, 215001 (2012)].

Enhanced proton acceleration by an ultrashort laser interaction with structured dynamic plasma targets

We experimentally demonstrate a notably enhanced acceleration of protons to high energy by relatively modest ultrashort laser pulses and structured dynamical plasma targets. Realized by special deposition of snow targets on sapphire substrates and using carefully planned prepulses, high proton yields emitted in a narrow solid angle with energy above 21 MeV were detected from a 5 TW laser. Our simulations predict that using the proposed scheme protons can be accelerated to energies above 150 MeV by 100 TW laser systems.

Measurements of the highest acceleration gradient for ions produced with a long laser pulse

Ultrafast plasma light ion streams have been produced using the 300 ps, kJ-class iodine laser, operating at PALS Centre in Prague. Ion detection was performed through standard ion collectors (IC) in time-of-flight configuration (TOF), shielded by thin metallic absorbers. This new diagnostics technique has been theoretically studied and experimentally tested in order to cut the long photopeak contribution and to analyze the ultrafast particle signal. Processing the obtained experimental IC-TOF data, including deconvolution processes of the TOF signals, UV/soft-x-ray photopeak absorption, and ion transmission calculations for different metallic filters, is shown. Mainly amorphous carbon (graphite) targets have been irradiated in order to limit the maximum number of ion charge states and to focus our study on demonstrating the validity of the proposed investigation technique. Maximum ion energy and acceleration gradient estimations as a function of the laser energy and focal spot diameter are reported.

High-energy, high-resolution x-ray imaging on the Trident short-pulse laser facility

With the completion of the Trident laser facility upgrade, 200 TW high-energy laser pulses are now capable of producing x-ray pulses with energies in the range of 15-40 keV, which will be used for high-spatial resolution radiography. A diagnostic suite is being developed on the laser system to investigate and characterize the x-ray emission from high-Z targets. This includes charge coupled device based single-photon counters, imaging plates, a high-energy electronic imager, spectral diagnostics, and optical and x-ray spot size diagnostics. We describe recent x-ray results from a commissioning campaign as well as describe the development and design of a high-energy spectrometer. X-ray radiographs taken at 22 keV with a spatial resolution of 25 mum are a first demonstration on this facility of high-energy, high-spatial resolution capability.

A novel backscatter focus diagnostic for the TRIDENT 200 TW laser

Here we present the first direct focal spot images and analysis of an ultrahigh intensity short-pulse laser focus (>5x10(19) W/cm(2)) on target. Such a focal spot characterization is typically done previous to the shot with a low-power alignment beam using equivalent plane imaging techniques. The resulting intensity of the shot is then inferred from these results. We report on the development of a backscatter focus diagnostic, which enables imaging of the on-target full-power focal spot.