On the study of hydrodynamic instabilities in the presence of background magnetic fields in high-energy-density plasmas

Blast-wave-driven hydrodynamic instabilities are studied in the presence of a background B-field through experiments and simulations in the high-energy-density(HED)physics regime.In experiments conducted at the Laboratoire pour l’utilisation des lasers intenses(LULI),a laserdriven shock-tube platform was used to generate a hydrodynamically unstable interface with a prescribed sinusoidal surface perturbation,and short-pulse x-ray radiography was used to characterize the instability growth with and without a 10-T B-field.The LULI experiments were modeled in FLASH using resistive and ideal magnetohydrodynamics(MHD),and comparing the experiments and simulations suggests that the Spitzer model implemented in FLASH is necessary and sufficient for modeling these planar systems.These results suggest insufficient amplification of the seed B-field,due to resistive diffusion,to alter the hydrodynamic behavior.Although the ideal-MHD simulations did not represent the experiments accurately,they suggest that similar HED systems with dynamic plasma-β(=2μ_(0)ρv^(2)/B^(2))values of less than∼100 can reduce the growth of blast-wave-driven Rayleigh–Taylor instabilities.These findings validate the resistive-MHD FLASH modeling that is being used to design future experiments for studying B-field effects in HED plasmas.

miniSCIDOM: a scintillator-based tomograph for volumetric dose reconstruction of single laser-driven proton bunches

Laser plasma accelerators(LPAs)enable the generation of intense and short proton bunches on a micrometre scale,thus offering new experimental capabilities to research fields such as ultra-high dose rate radiobiology or material analysis.Being spectrally broadband,laser-accelerated proton bunches allow for tailored volumetric dose deposition in a sample via single bunches to excite or probe specific sample properties.The rising number of such experiments indicates a need for diagnostics providing spatially resolved characterization of dose distributions with volumes of approximately 1 cm^(3) for single proton bunches to allow for fast online feedback.Here we present the scintillator-based miniSCIDOM detector for online single-bunch tomographic reconstruction of dose distributions in volumes of up to approximately 1 cm^(3).The detector achieves a spatial resolution below 500μm and a sensitivity of 100 mGy.The detector performance is tested at a proton therapy cyclotron and an LPA proton source.The experiments’primary focus is the characterization of the scintillator’s ionization quenching behaviour.

Short-pulse laser-driven x-ray radiography

We have developed a new radiography setup with a short-pulse laser-driven x-ray source. Using a radiography axis perpendicular to both long- and short-pulse lasers allowed optimizing the incident angle of the short-pulse laser on the x-ray source target. The setup has been tested with various x-ray source target materials and different laser wavelengths.Signal to noise ratios are presented as well as achieved spatial resolutions. The high quality of our technique is illustrated on a plasma flow radiograph obtained during a laboratory astrophysics experiment on POLARs.

OCTOPOD:single-bunch tomography for angular-spectral characterization of laser-driven protons

Laser-plasma accelerated(LPA)proton bunches are now applied for research fields ranging from ultra-high-dose-rate radiobiology to material science.Yet,the capabilities to characterize the spectrally and angularly broad LPA bunches lag behind the rapidly evolving applications.The OCTOPOD translates the angularly resolved spectral characterization of LPA proton bunches into the spatially resolved detection of the volumetric dose distribution deposited in a liquid scintillator.Up to 24 multi-pinhole arrays record projections of the scintillation light distribution and allow for tomographic reconstruction of the volumetric dose deposition pattern,from which proton spectra may be retrieved.Applying the OCTOPOD at a cyclotron,we show the reliable retrieval of various spatial dose deposition patterns and detector sensitivity over a broad dose range.Moreover,the OCTOPOD was installed at an LPA proton source,providing real-time data on proton acceleration performance and attesting the system optimal performance in the harsh laser-plasma environment.

Three-dimensional acoustic monitoring of laser-accelerated protons in the focus of a pulsed-power solenoid lens

The acoustic pulse emitted from the Bragg peak of a laser-accelerated proton bunch focused into water has recently enabled the reconstruction of the bunch energy distribution.By adding three ultrasonic transducers and implementing a fast data analysis of the filtered raw signals,I-BEAT(Ion-Bunch Energy Acoustic Tracing)3D now provides the mean bunch energy and absolute lateral bunch position in real-time and for individual bunches.Relative changes in energy spread and lateral bunch size can also be monitored.Our experiments at DRACO with proton bunch energies between 10 and 30 MeV reveal sub-MeV and sub-mm resolution.In addition to this 3D bunch information,the signal strength correlates also with the absolute bunch particle number.