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Register a new userPracticality of magnetic compression for plasma density control
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Plasma densification through magnetic compression has been suggested for time-resolved control of the wave properties in plasma-based accelerators. Using particle in cell simulations with real mass ratio, the practicality of large magnetic compression on timescales shorter than the ion gyro-period is investigated. For compression times shorter than the transit time of a compressional Alfven wave across the plasma slab, results show the formation of two counter-propagating shock waves, leading to a highly non-uniform plasma density profile. Furthermore, the plasma slab displays large hydromagnetic like oscillations after the driving field has reached steady state. Peak compression is obtained when the two shocks collide in the mid-plane. At this instant, very large plasma heating is observed, and plasma $beta$ is estimated to be about $1$. Although these results point out a densification mechanism quite different and more complex than initially envisioned, these features could possibly be advantageous in particle accelerators.
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It is proposed a new method of compressing laser pulse by fast extending plasma gratings(FEPG), which is created by ionizing the hypersound wave generated by stimulated Brillouin scattering(SBS) in the background gas. Ionized by a short laser pulse, the phonon forms a light-velocity FEPG to fully reflect a resonant pump laser. As the reflecting surface moves with a light velocity, the reflected pulse is temporally overlapped and compressed. This regime is supported by the simulation results of a fully kinetic particle-in-cell(PIC) code Opic with a laser wavelength of 1um, displaying a pump pulse is compressed from 13ps to a few cycles(7.2fs), with an efficiency close to 80%. It is a promising method to produce critical laser powers due to several features: high efficiency without a linear stage, robustness to plasma instabilities, no seed and a wide range of pump intensity.
This paper presents the conceptual design of a high-voltage pulser intended to generate 30-T magnetic fields for magneto-inertial fusion experiments at the OMEGA facility. The pulser uses a custom capacitor bank and two externally triggered spark gaps to drive a multi-turn coil. This new high-voltage pulser is capable of storing 10 times more energy than the previous system, using a higher charge voltage (from 20 to 30 kV) and a larger capacitance (from 1 {mu}F to 5 {mu}F). Circuit simulations show that this pulser can deliver 100 kA into a 60-nH, 14-m{Omega} coil with a rise time of 1 {mu}s. For a coil with 2 turns with an average coil diameter of 7.8 mm, this current translates into a 32-T peak magnetic field at coil center. This is a factor of three increase in the peak magnetic field compared to the present generator magnetic field capabilities.
Production of antihydrogen atoms by mixing antiprotons with a cold, confined, positron plasma depends critically on parameters such as the plasma density and temperature. We discuss non-destructive measurements, based on a novel, real-time analysis of excited, low-order plasma modes, that provide comprehensive characterization of the positron plasma in the ATHENA antihydrogen apparatus. The plasma length, radius, density, and total particle number are obtained. Measurement and control of plasma temperature variations, and the application to antihydrogen production experiments are discussed.
We report the highest compression reached in laboratory plasmas using eight laser beams, E$_{laser}$$approx$12 kJ, $tau_{laser}$=2 ns in third harmonic on a CD$_2$ target at the ShenGuang-II Upgrade (SGII-Up) facility in Shanghai, China. We estimate the deuterium density $rho_D$= 2.0 $pm$ 0.9 kg/cm$^{3}$, and the average kinetic energy of the plasma ions less than 1 keV. The highest reached areal density $Lambda rho_{D}$=4.8 $pm$ 1.5 g/cm$^{2}$ was obtained from the measured ratio of the sequential ternary fusion reactions (dd$rightarrow$t+p and t+d$rightarrow$$alpha$+n) and the two body reaction fusions (dd$rightarrow$$^3$He+n). At such high densities, sequential ternary and also quaternary nuclear reactions become important as well (i.e. n(14.1 MeV) + $^{12}$C $rightarrow$ n+$^{12}$C* etc.) resulting in a shift of the neutron (and proton) kinetic energies from their birth values. The Down Scatter Ratio (DSR-quaternary nuclear reactions) method, i.e. the ratio of the 10-12MeV neutrons divided by the total number of 14.1MeV neutrons produced, confirms the high densities reported above. The estimated lifetime of the highly compressed plasma is 52 $pm$ 9 ps, much smaller than the lasers pulse duration.
Three-dimensional FLASH radiation-magnetohydrodynamics (radiation-MHD) modeling is carried out to study the hydrodynamics and magnetic fields in the shock-shear derived platform. Simulations indicate that fields of tens of Tesla can be generated via Biermann battery effect due to vortices and mix in the counter-propagating shock-induced shear layer. Synthetic proton radiography simulations using MPRAD and synthetic X-ray image simulations using SPECT3D are carried out to predict the observable features in the diagnostics. Quantifying the effects of magnetic fields in inertial confinement fusion (ICF) and high-energy-density (HED) plasmas represents frontier research that has far-reaching implications in basic and applied sciences.
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