| 1. |
- Ahmed, Hamad, et al.
(författare)
-
Experimental Observation of Thin-shell Instability in a Collisionless Plasma
- 2017
-
Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing (IOPP). - 2041-8205 .- 2041-8213. ; 834:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balance between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.
|
|
| 2. |
- Ahmed, Hamad, et al.
(författare)
-
Time-Resolved Characterization of the Formation of a Collisionless Shock
- 2013
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110:20
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the temporally and spatially resolved detection of the precursory stages that lead to the formation of an unmagnetized, supercritical collisionless shock in a laser-driven laboratory experiment. The measured evolution of the electrostatic potential associated with the shock unveils the transition from a current free double layer into a symmetric shock structure, stabilized by ion reflection at the shock front. Supported by a matching particle-in-cell simulation and theoretical considerations, we suggest that this process is analogous to ion reflection at supercritical collisionless shocks in supernova remnants.
|
|
| 3. |
- Dieckmann, Mark Eric, et al.
(författare)
-
The Weibel instability in a circular rarefaction wave
- 2012
-
Ingår i: Proceedings of the 39th European Physical Society Conference & 16th Int. Congress on Plasma Physics. ; , s. P1.176-1-P1.176-4
-
Konferensbidrag (refereegranskat)abstract
- Instabilities behind the front of a cylindrically expanding plasma have been investigated experimentally and with a particle-in-cell simulation. Tubelike filamentary structures form behind the front of a plasma created by irradiating wire targets with a ps-duration and intense ( 1019 W cm-2) laser pulse. These filaments exhibit coherent magnetic fields with a remarkable stability ( 103 / wp: plasma frequency). PIC simulations indicate that an instability driven by a thermal anisotropy of the electron population is the cause. This instability requires a plasma density gradient and hot electrons. It can thus contribute to the generation of strongsustained magnetic fields in astrophysical jets.
|
|
| 4. |
- Quinn, K., et al.
(författare)
-
Weibel-Induced Filamentation during an Ultrafast Laser-Driven Plasma Expansion
- 2012
-
Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007 .- 1079-7114. ; 108:13, s. 135001-
-
Tidskriftsartikel (refereegranskat)abstract
- The development of current instabilities behind the front of a cylindrically expanding plasma has been investigated experimentally via proton probing techniques. A multitude of tubelike filamentary structures is observed to form behind the front of a plasma created by irradiating solid-density wire targets with a high-intensity (I∼1019 W/cm2), picosecond-duration laser pulse. These filaments exhibit a remarkable degree of stability, persisting for several tens of picoseconds, and appear to be magnetized over a filament length corresponding to several filament radii. Particle-in-cell simulations indicate that their formation can be attributed to a Weibel instability driven by a thermal anisotropy of the electron population. We suggest that these results may have implications in astrophysical scenarios, particularly concerning the problem of the generation of strong, spatially extended and sustained magnetic fields in astrophysical jets.
|
|
| 5. |
- Sarri, Gianluca, et al.
(författare)
-
Dynamics of Self-Generated, Large Amplitude Magnetic Fields Following High-Intensity Laser Matter Interaction
- 2012
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 109:20, s. 205002-
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of magnetic fields with an amplitude of several tens of megagauss, generated at both sides of a solid target irradiated with a high-intensity (∼1019 W/cm2) picosecond laser pulse, has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and simple analytical modeling, may have implications for ion acceleration driven by the plasma sheath at the rear side of the target as well as for the laboratory study of self-collimated high-energy plasma jets.
|
|
| 6. |
- Sarri, Gianluca, et al.
(författare)
-
Observation and characterization of laser-driven phasespace electron holes
- 2010
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 17:1, s. 010701-
-
Tidskriftsartikel (refereegranskat)abstract
- The direct observation and full characterization of a phase space electron hole (EH) generated during laser-matter interaction is presented. This structure, propagating in a tenuous, nonmagnetized plasma, has been detected via proton radiography during the irradiation with a ns laser pulse (I21014 W/cm2) of a gold hohlraum. This technique has allowed the simultaneous detection of propagation velocity, potential, and electron density spatial profile across the EH with fine spatial and temporal resolution allowing a detailed comparison with theoretical and numerical models.
|
|
