Sprecher
Beschreibung
Kinetic plasma instabilities such as two-stream [1], filamentation [2] and Weibel [3] instabilities arising from anisotropic electron velocity distributions (EVDs) involve in many scenarios, for instance, electron beam transport in plasmas [4-5], collisionless shocks [6], laser-created colliding plasmas [7-8] and instability mediated gamma ray flashes [9]. These instabilities have been extensively investigated in theory and simulations yet there have been only a handful direct laboratory verifications of these instabilities due to the lack of a suitable platform that would allow initialization of known EVDs. Here we demonstrate a relatively simple laboratory platform that utilizes optical field ionized plasmas which have anisotropic EVDs for studying kinetic plasma instabilities. We show that when high-density plasmas (1018-1019 cm-3) are formed by sequentially ionizing both helium electrons using a circularly polarized (CP) laser, the streaming and filamentation instabilities grow and saturate in ~one ps and decay as a result of collisionless phase space diffusion and particle trapping. Thereafter a Weibel instability starts to grow in the plasma. The polarization dependent frequency and growth rates of these kinetic instabilities, measured using Thomson scattering of a probe laser, agree well with the kinetic theory and simulations.
References
[1] T. H. Stix, “Waves in Plasmas”, Springer Science & Business Media, 1992.
[2] B. D. Fried, “Mechanism for Instability of Transverse Plasma Waves”, Phys. Fluids. 2, 337 (1959).
[3] E. S. Weibel, “Spontaneously Growing Transverse Waves in a Plasma Due to an Anisotropic Velocity Distribution”, Phys. Rev. Lett. 2, 83 (1959).
[4] B. Allen et al., Experimental Study of Current Filamentation Instability. Phys. Rev. Lett. 109, 185007 (2012).
[5] C. M. Huntington et al., Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows. Nat. Phys. 11, 173–176 (2015).
[6] F. Fiuza, R. A. Fonseca, J. Tonge, W. B. Mori, L. O. Silva, Weibel-Instability-Mediated Collisionless Shocks in the Laboratory with Ultraintense Lasers. Phys. Rev. Lett. 108, 235004 (2012).
[7] W. Fox et al., Filamentation Instability of Counterstreaming Laser-Driven Plasmas. Phys. Rev. Lett. 111, 225002 (2013).
[8] C. M. Huntington et al., Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows. Nat. Phys. 11, 173–176 (2015).
[9] A. Benedetti, M. Tamburini, C. H. Keitel, Giant collimated gamma-ray flashes. Nat. Photonics. 12, 319–323 (2018).
| Working group | Laser-driven electron acceleration |
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