Magnetic Explosions

Physics- …, 2008

Recent experimental and theoretical investigations are reviewed concerning the generation of fast charged particles and superstrong magnetic fields in the interaction of ultrashort laser pulses with solid targets. The mechanisms of generating fast charged particles in superstrong light fields of laser radiation with intensities ranging from 10 17 to 10 21 W cm ±2 are considered. Electron acceleration due to vacuum heating, the ponderomotive potential, resonance absorption, the laserdriven wake field in the underdense part of plasma, cyclotron mechanism and some other mechanisms are thoroughly analyzed. Experimental data on the acceleration of protons and atomic ions by spatial charge fields on thin and thick solid targets are presented and theoretically interpreted. Particular attention is paid to the generation of superstrong quasistatic magnetic fields in laser plasmas and methods for measuring them under the action of various laser pulses of both femtoand picosecond durations. The possible formation of magnetic plasma configurations and magnetic plasma confinement are discussed.

Fusion Science and Technology, 2005

The results of <<MHD>> experiment with quasispherical Laser-produced Plasma Clouds (LPC) expanding into strong (Bâ â10 kG) and uniform magnetic field at KI-1 facility of ILP are presented. Main characteristics and the influence of non-MHD flute instability onto effectiveness of plasma-field interaction were studied especially for the purpose of plasma confinement and the direct conversion of its kinetic energy into

Physical review letters, 2002

We demonstrate ultrashort (6 ps), multi-Megagauss (27 MG) magnetic pulses generated upon interaction of an intense laser pulse (10 16 Wcm −2 , 100 fs) with a solid target. The temporal evolution of these giant fields generated near the high density critical layer is obtained with the highest resolution reported so far. Particle-in-cell simulations and phenomenological modeling is used to explain the results. The first direct observations of anomalously rapid damping of plasma shielding currents produced in response to the hot electron currents penetrating the bulk plasma are presented.

Matter and Radiation at Extremes, 2021

This paper was selected as an Editor's Pick ARTICLES YOU MAY BE INTERESTED IN Studies of laser-plasma interaction physics with low-density targets for direct-drive inertial confinement fusion on the Shenguang III prototype Matter and Radiation at Extremes 6, 025902 (2021);

Nature Physics, 2014

X-ray 1-3 and radio 4-6 observations of the supernova remnant Cassiopeia A reveal the presence of magnetic fields about 100 times stronger than those in the surrounding interstellar medium. Field coincident with the outer shock probably arises through a nonlinear feedback process involving cosmic rays 2,7,8 . The origin of the large magnetic field in the interior of the remnant is less clear but it is presumably stretched and amplified by turbulent motions. Turbulence may be generated by hydrodynamic instability at the contact discontinuity between the supernova ejecta and the circumstellar gas 9 . However, optical observations of Cassiopeia A indicate that the ejecta are interacting with a highly inhomogeneous, dense circumstellar cloud bank formed before the supernova explosion 10-12 . Here we investigate the possibility that turbulent amplification is induced when the outer shock overtakes dense clumps in the ambient medium . We report laboratory experiments that indicate the magnetic field is amplified when the shock interacts with a plastic grid. We show that our experimental results can explain the observed synchrotron emission in the interior of the remnant. The experiment also provides a laboratory example of magnetic field amplification by turbulence in plasmas, a physical process thought to occur in many astrophysical phenomena. High-resolution X-ray images and radio polarization maps of Cassiopeia A show two distinct strong magnetic field regions . Narrow X-ray filaments, a fraction of a parsec in width, are observed at the outer shock rim at a radius of about 2.5 pc. These structures are produced by synchrotron radiation from ultrarelativistic electrons (with teraelectronvolt energy) and can be explained by magnetic fields of the order of 100 µG or more 2,3 . The interior of the remnant contains a disordered shell (about 0.5 pc in width at a radius of 1.7 pc) of radio synchrotron emission by gigaelectronvolt electrons 4 . The inferred magnetic field in these radio knots is a few milligauss, about 100 times higher than expected from the standard shock compression of

Physics of Plasmas

Physics of Plasmas, 2012

We present experiments on the Trident laser facility at Los Alamos National Laboratory which demonstrate key elements in the production of laser-driven, magnetized, laboratory-scaled astrophysical collisionless shocks. These include the creation of a novel magnetic piston to couple laser energy to a background plasma and the generation of a collisionless shock precursor. We also observe evidence of decoupling between a laser-driven fast ion population and a background plasma, in contrast to the coupling of laser-ablated slow ions with background ions through the magnetic piston. 2D hybrid simulations further support these developments and show the coupling of the slow to ambient ions, the formation of a magnetic and density compression pulses consistent with a collisionless shock, and the decoupling of the fast ions. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4736846]

Physics Reports, 1982

Introduction 3 10. Shock structure and ionization relaxation 45 2. Formulation of the problem. Basic equations 5 11. Formation of a magnetic structure of a GD shock pro-3. Magnetic structures of ionizing shock waves 10 pagating across the magnetic field 48 4. Evolutionarity conditions and the number of boundary 12. Magnetic structures of normal ionizing shock waves 54 conditions for ionizing shock waves 19 13. Self-similar piston problem 59 5. Precursor ionization. Ionization stability 26 14. Plasma heating in normal ionizing shock waves 64 6. The additional relation and magnetic structures of shock 15. Normal ionizing shock waves. Numerical simulation of waves 31 flow ahead of a conducting piston 72 7. Limiting regimes 34 16. Switch-off shock waves 79 8. Transverse shock waves (qualitative theory) 37 References 83 9. Shock structure of a transverse ionizing shock wave 41

Plasma and Fusion Research, 2009

This review covers recent developments in multi-hundred-TW femtosecond laser systems and progress in intense laser-plasma interactions at the Institute of Physics, Chinese Academy of Sciences. The peak power of the institute's Xtreme Light III (XL-III) laser system has been upgraded from 350 to 725 TW, and the system used to observe the lateral transport of fast electrons due to magnetic and electrostatic fields at target surfaces. The surface fields cause fast-electron beams to be emitted along the front and rear target surfaces. Confinement and guiding of fast-electron propagation is demonstrated with wire-or wedge-shaped targets. Longitudinal transport is detected by optical and ion emission. Numerical simulations show that quasi-monoenergetic ion beams can be generated by collisionless electrostatic shock acceleration and phase-stable acceleration with a circularly polarized laser field. A new mechanism for high-power THz emission with plasmas as media is proposed; it can be used to obtain a single-cycle THz emission. The conversion efficiency from laser energy to K α X-ray emission in a laser-copper target interaction is increased to 10 −4 using high-contrast laser pulses.

2013

Laboratory generation of strong magnetic fields opens new frontiers in plasma and beam physics, astro-and solar-physics, materials science, and atomic and molecular physics. Although kilotesla magnetic fields have already been produced by magnetic flux compression using an imploding metal tube or plasma shell, accessibility at multiple points and better controlled shapes of the field are desirable. Here we have generated kilotesla magnetic fields using a capacitor-coil target, in which two nickel disks are connected by a U-turn coil. A magnetic flux density of 1.5 kT was measured using the Faraday effect 650 mm away from the coil, when the capacitor was driven by two beams from the GEKKO-XII laser (at 1 kJ (total), 1.3 ns, 0.53 or 1 mm, and 5 3 10 16 W/cm 2 ). L aboratory generation of strong, shaped magnetic fields offers a new experimental test bed to study plasma and beam physics 1 , astro-2 and solar-physics 3,4 , materials science 5 , and atomic and molecular physics 6 . In fastignition laser fusion research, collimation of a relativistic electron beam by an axial magnetic field is a key scheme to increase the coupling efficiency between the laser and the core 7 . Magnetic field reconnection 3,4 and collisionless shock generation 1 in a plasma subject to a strong magnetic field are also current research objectives.