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Hantao Ji Princeton Plasma Physics Laboratory

Hantao Ji Princeton Plasma Physics Laboratory. Experimentalist Laboratory astrophysics Reconnection, angular momentum transport, dynamo effect… Center for Magnetic Self-organization (CMSO, a NSF Physics Frontier Center) Current main research projects (>~10%)

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Hantao Ji Princeton Plasma Physics Laboratory

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  1. Hantao JiPrinceton Plasma Physics Laboratory • Experimentalist • Laboratory astrophysics • Reconnection, angular momentum transport, dynamo effect… • Center for Magnetic Self-organization (CMSO, a NSF Physics Frontier Center) • Current main research projects (>~10%) • Magnetic Reconnection Experiment (MRX) • Magnetorotational Instability (MRI) liquid gallium experiment • Plasma MRI experiment • Free-surface liquid gallium experiment • Madison Symmetric Torus (MST) experiment • Field Reversed Configuration (FRC) experiment • National Spherical Torus experiment (NSTX) • Interests: • Collisionless shocks

  2. Magnetic Reconnection Magnetospheric plasma Laboratory plasmas Solar plasma More distant astrophysical plasmas

  3. Fundamental Physics Questions for Magnetic Reconnection • How does reconnection start? (The trigger problem) • Why reconnection is fast compared to classical theory? • How ions and electrons are heated or accelerated? • How to apply local reconnection physics to a large system? • …

  4. Magnetic Reconnection Experiment (MRX)

  5. Experimental Setup in MRX Well-controlled and diagnosed experiment

  6. Realization of Stable Current Sheet and Quasi-steady Reconnection

  7. Reconnection Rates Agree with a Generalized Sweet-Parker Model (Ji et al. PRL ‘98) • The model modified to take into account of • Measured enhanced resistivity • Compressibility • Higher pressure in downstream than upstream model

  8. Why Dissipation is Enhanced at Low Collisionalities? Turbulence or Hall effect Ji et al. PRL (‘04) Ren et al. PRL (‘05)

  9. Both Observed in Magnetospheric Reconnection (Mozer et al., PRL 2002) (Bale et al. ‘04) EM ES Q’field Polar Satellite

  10. Reconnection Rate Also Affected by System Size

  11. HH30 By HST Angular Momentum Transport in Accretion Disks • Many important processes happen in accretion disks: • Formation of stars and planets in proto-star systems • Mass transfer and energetic activity in binary stars • Release of energy (as luminous as 1015 of Sun) in quasars and AGNs • The Problem: why accretion is fast? Or equivalently why angular momentum outward transport is fast? • Two Candidate Mechanisms to Generate Turbulence • Hot disks: highly electrically conducting  Magnetorotational Instability (MRI) • Cold disks: perhaps insufficiently conducting for MRI, but essentially inviscid  nonlinear instability at large Reynolds #s

  12. Basic Idea: Magnetized Taylor-Couette Flow of Liquid Gallium • Centrifugal force balanced by pressure force from the outer wall • MRI destabilized with appropriate 1, 2 and Bz in a table-top size. • Identical dispersion relation as in accretion disks in incompressible limit Bz < 1T Ga Not tosimulate accretion disks, but to study basic physics

  13. Water Results: Negligible Transport Found in Quasi-Keplerian Flows Re based on inner cylinder Re based on outer cylinder

  14. No Signs of Turbulence up to Re=210^6 Split-ring cases • Large Reynolds stress detected if • Boundary conditions not optimum, or • Even with optimum boundary conditions, but at smaller Re’s • =(0.722.7)10-6, or <6.210-6 with 98% confidence, as compared to required ~103 •  unlikely larger at even larger Re’s, as in pipe flows and also by theoretical arguments (Lesur & Longaretti, 2005) RZ99 Ji et al, Nature 444, 343 (2006)

  15. Summary

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