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Electron scale magnetic reconnection in a laser produced plasma

Electron scale magnetic reconnection in a laser produced plasma. Yasuhiro Kuramitsu ILE, Osaka University HEDLA2012 Tallahassee, FL, April 30- May 4, 2012.

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Electron scale magnetic reconnection in a laser produced plasma

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  1. Electron scale magnetic reconnection in a laser produced plasma • Yasuhiro Kuramitsu • ILE, Osaka University • HEDLA2012 • Tallahassee, FL, April 30- May 4, 2012

  2. Y. Kuramitsu1, T. Moritaka1, Y. Sakawa1, T. Morita1, T. Ide2, K. Nishio3, C. D. Gregory4, J. N. Waugh5, B. Loupias4, G. Gregori6, M. Koenig4, N. Woolsey5, T. Sano1, K. Tomita7, K. Uchino7, M. Hoshino8, and H. Takabe1 1 Institute of Laser Engineering, Osaka University 2 Graduate School of Engineering, Osaka University 3 Graduate School of Science, Osaka University 4 Laboratoire pour l'Utilisation des Lasers Intenses, Ecole Polytechnique, France 5 Department of Physics, University of York, UK 6 Department of Physics, University of Oxford, UK 7 Interdisciplinary Graduate School of Engineering Sciences, Kyushu University 8 Department of Earth and Planetary Science, University of Tokyo

  3. Outline • Jet formation in the presence of a weak magnetic field • Reconnection governed by electron dynamics

  4. Astrophysical jet Factors believed to affect collimation: • Ambient medium • Radiative cooling • Magnetic fields

  5. Laboratory simulation of astrophysical jet • Shigemori+ 2000 PRE, Mizuta+ 2002 ApJ • effect of radiative cooling • Remington, Drake and Ryutov, RMP, 2006 • review of recent studies in laboratory astrophysics • Loupias et al., PRL, 2007 • measurement of scaling parameters • Gregory+ 2008 ApJ, Gregory+ 2008 PPCF, Waugh+ 2009 Ap&SS • effect of ambient gas • Kuramitsu+ 2009 ApJL • effect of ambient plasma • Effect of magnetic field to be done

  6. GXII 4 beams, 500 J, 500 ps offsets 200 - 300 μm for directional expansion Single CH plane target 10 μm External magnetic field a permanent magnet ~ 0.7 T at the surface 0.3 T at laser position perpendicular to the plasma axis Target environment: vacuum Jet formation in the presence of an external magnetic field

  7. Without an external magnetic field With an external magnetic field B Main laser Main laser Thin CH plane Thin CH plane Interferograms Collimation observed only when B exist.

  8. Plasma parameters • plasma velocity vi ~ 500 km/s • magnetic field B ~ 0.3 T • electron density ne = Zni ~ 1019 cm-3 • dynamic plasma beta nimivi2/(B2/μ0) ~ 1.1x105 • Such a weak field affects the plasma propagation. • ion gyroradius ~ 32 mm • larger than our system size of ~ 10 mm • electron gyroradius ~ 9.5 μm • electrons are magnetized

  9. Lathrop and Forest, July 2011 Physics Today Possible mechanism • Field distortion by strong dynamic pressure resulting in local parallel field.

  10. Lathrop and Forest, July 2011 Physics Today Possible mechanism + + + + + + - - - - - + - - - - - - - - - - + + + + + + + • Charge separation due to the electron trapping by the field. • E field across the distorted B field

  11. - + Possible mechanism Space charge JxB force + = ⨂ B J JxB force • ExB drift only for electrons • Current formation, JxB enhances the collimation • J generates B field, enhancing the distortion • Positive feedback

  12. Particle-in-Cell simulation • Plasma Injection +Vx • Injection velocity > thermal speed • Vx/Vte = 2.2 , Vx/Vti = 11 • High beta value • β = 484 • External magnetic field +By • perpendicular to plasma injection • spatially uniform • Numerical parameters • ~ 108 particles • (1024×1024) uniform grid By Vx B = 1 Vx

  13. Particle-in-Cell simulation Induced magnetic field (C) induced current density (A) charge density Ex By Vx ES field (D) collimation in deformed field (e-) (B) perpendicular flow field-aligned electron flow Jz e, i electron perpendicular E×B motion Total magnetic field

  14. Electron dynamics governs the global structure! • One interesting application is reconnection.

  15. ⨂ Ambient plasma External pressure + = Reconnection? • Adding an ambient plasma enhances the field distortion and plasma collimation by the external pressure. • Thinning the structure may result in reconnection.

  16. External B and P B reconnection site plasmoid Main laser Thin CH plane Ambient plasma Experiment (preliminary) self emission 35 ns

  17. elongated plasma plasmoid Experiment (preliminary) self emission optical pyrometry • separation velocity ∆ v ~ 26 km/s • initial Alfvén velocity cA0 ~ 1.5 km/s • If B and n are enhanced by x12 and x2, then cA ~ ∆ v/2 plasmoid

  18. Summary • Jet formation in the presence of a weak perpendicular magnetic field • First experimental evidence of electron dynamics governing the global structure • Electron scale reconnection

  19. Particle-in-Cell simulation ion and electron densities in Log sale & Magnetic filed

  20. Particle-in-Cell simulation • Plasma Injection +Vx • Injection velocity > thermal speed • Vx/Vte = 2.2 , Vx/Vti = 11 • High beta value • β = 24.1 (finite B case) • External magnetic field +By • perpendicular to plasma injection • spatially uniform • Numerical parameters • ~ 108 particles • (1024×1024) uniform grid By Vx B = 1 Vx

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