Ultra-intense MeV photon and neutron beams are indispensable tools in many research fields such as nuclear, atomic and material science as well as in medical and biophysical applications. For ...applications in laboratory nuclear astrophysics, neutron fluxes in excess of 10
n/(cm
s) are required. Such ultra-high fluxes are unattainable with existing conventional reactor- and accelerator-based facilities. Currently discussed concepts for generating high-flux neutron beams are based on ultra-high power multi-petawatt lasers operating around 10
W/cm
intensities. Here, we present an efficient concept for generating γ and neutron beams based on enhanced production of direct laser-accelerated electrons in relativistic laser interactions with a long-scale near critical density plasma at 10
W/cm
intensity. Experimental insights in the laser-driven generation of ultra-intense, well-directed multi-MeV beams of photons more than 10
ph/sr and an ultra-high intense neutron source with greater than 6 × 10
neutrons per shot are presented. More than 1.4% laser-to-gamma conversion efficiency above 10 MeV and 0.05% laser-to-neutron conversion efficiency were recorded, already at moderate relativistic laser intensities and ps pulse duration. This approach promises a strong boost of the diagnostic potential of existing kJ PW laser systems used for Inertial Confinement Fusion (ICF) research.
We report on enhanced laser driven electron beam generation in the multi MeV energy range that promises a tremendous increase of the diagnostic potential of high energy sub-PW and PW-class laser ...systems. In the experiment, an intense sub-picosecond laser pulse of ∼1019 Wcm−2 intensity propagates through a plasma of near critical electron density (NCD) and drives the direct laser acceleration (DLA) of plasma electrons. Low-density polymer foams were used for the production of hydrodynamically stable long-scale NCD-plasmas. Measurements show that relativistic electrons generated in the DLA-process propagate within a half angle of 12 ± 1° to the laser axis. Inside this divergence cone, an effective electron temperature of 10-13 MeV and a maximum of the electron energy of 100 MeV were reached. The high laser energy conversion efficiency into electrons with energies above 2 MeV achieved 23% with a total charge approaching 1 μC. For application purposes, we used the nuclear activation method to characterize the MeV bremsstrahlung spectrum produced in the interaction of the high-current relativistic electrons with high-Z samples and measured top yields of gamma-driven nuclear reactions. The optimization of the high-Z target geometry predicts an ultra-high MeV photon number of ∼1012 per shot at moderate relativistic laser intensity of 1019 Wcm−2. A good agreement between the experimental data and the results of the 3D-PIC and GEANT4-simulations was demonstrated.
A technique for measuring the spatial heterogeneity of the light yield of a proton radiography scintillator has been developed. It is based on the recording of digital images formed during the ...passage of a proton beam through a scintillator and the approximation of the intensity distribution in the beam cross section by a two-dimensional Gaussian-like function. The results of the spatial calibration of the light yield of a lutetium silicate scintillator obtained using a magneto-optical proton microscope PUMA are presented. It is shown that accounting of the spatial heterogeneity of the scintillator makes it possible to describe the transverse beam intensity at each point of the proton radiographic image with a mean accuracy of about 0.7%. Experimental data on fluctuations in the position of the beam center, its size, and shape in the scintillator plane of PUMA microscope were obtained. The proposed technique eliminates optical artifacts in the radiographic image caused by operation of the optical recording system and artifacts caused by the electron-optical shutter, provided that the signal is proportional to the intensity of the beam. It also eliminates or strongly suppresses optical artifacts in radiographic images due to changes in the efficiency of a charge-coupled digital camera.
The upcoming experiments on heating targets using intense beams of heavy ions to be carried out within the scope of the FAIR (Facility for Antiproton and Ion Research) project require measuring the ...profile of the beam on the target to estimate the optimal energy uptake by materials exposed and to interpret accurately experimental results. We propose a method to diagnose the transverse distribution of intensity of ions through registering X-rays generated by the target as a result of the incident ion beam. The numerical code Geant4 is used to develop and design a full-scale experimental model to proceed with simulating X-ray diagnostics of the ion beam. The UNILAC accelerator (GSI, Germany) is used to validate the method proposed and compare it with the results of simulation. An Au
+26
ion beam (energy of 11.4 MeV/a.m.u.) is passed through a copper target 10 μm thick. The X-ray image of the target is formed on a CsI scintillator using a pinhole camera. The image is recorded using a digital sCMOS camera having a brightness amplifier.
In accelerator physics, the method of absorption filters is used for measurements of the energy spectrum of electrons with energy above 100 keV. In this paper, we present a modification of the method ...to measure the delta-like spectrum of electron beams based on fitting by statistical distributions the initial experimental data and the results of simulation of the beam transmission through the filters. The method developed is much more accurate and stable than the original one and is consistent with the direct measurements by a magnetic spectrometer.
The interaction of a heavy-ion beam with matter is a fundamental problem of plasma physics and high-energy density in matter physics. The paper presents the results of experimental studies of energy ...losses of Fe
+2
ions with an energy of 100 keV/u in a hydrogen plasma. The experimental data of plasma free electron stopping power are compared with theoretical models.
A method for reconstruction of the volume density distribution in dynamic targets from their proton radiography image is considered. The reconstruction can be carried out using the inverse Abel ...transform under the assumption that the studied object and processes have radial symmetry. To increase the accuracy of reconstructed data, algorithms for correction of basic types of distortions of proton radiography images are proposed. The results of processing experimental data obtained on proton radiography facilities PUMA at ITEP and PRIOR at GSI are presented.
A digital model of a grazing-incidence X-ray spectrograph and methods for reconstruction of soft X-ray spectra of a Z-pinch plasma at the Angara-5-1 facility in the 2–40 nm range have been developed. ...The main problems hindering reliable qualitative and quantitative reconstruction of the initial Z-pinch X-ray spectra are the superposition of signals from different diffraction orders and the complex form of the device instrumental function. Two techniques for reconstructing the spectrum are presented. In the first one, a digital model of the spectrograph was developed in the Geant4 Monte Carlo simulation toolkit, taking into account the geometry of the experiment and the processes of interaction of X-ray radiation with a diffraction grating. In this model, taking into account the specific shape of the groove profile of the diffraction grating and the differential method for solving the diffraction problem, the X-ray intensity distribution in different diffraction orders depending on the wavelength is calculated. Using the developed model of the spectrograph, its instrumental function was calculated. The second technique does not use a specific grating groove shape, but, based on the analysis of calibration spectrograms, it constructs a dispersion relation and allows one to reconstruct the spectrum. At the end of the work, the results of reconstruction by the first and second techniques are compared and fairly good agreement between the spectra obtained by different techniques is shown.
Information about charged particles emitted by plasma of high-current discharges is of interest both from the point of view of understanding the fundamental processes occurring in pulsed plasma and ...for applied problems. Compact magnetic spectrometers based on permanent magnets make it possible to measure the flux of charged particles from a plasma under conditions of strong electromagnetic noise. Imaging plates (IP) are one of the most commonly used types of detectors for detecting charged particles in laser-plasma and electric-discharge experiments. This paper presents the results of calibration of the BAS-MS IP when detecting electrons and the BAS-TR IP when detecting helium and tungsten ions. Calibration dependences of the sensitivity of the BAS-MS IP for electrons in the energy range of 0.65–50 MeV and the sensitivity of the BAS-TR IP for tungsten ions in the energy range from 20 eV to 650 keV are obtained, taking into account the angles of incidence of particles on the detector.
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