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Collisionless Plasma Flow in External Magnetic Field

Collisionless Plasma Flow in External Magnetic Field. University of Nevada, Reno. 1D-PIC SIMULATION PARAMETER. Plasma fully ionized hydrogen plasma length : 4 mm collision frequency : ν ce = 2x 10 8 1/sec flow velocity u sw =4x10 7 cm/s External Magnetic Field profile :

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Collisionless Plasma Flow in External Magnetic Field

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  1. Collisionless Plasma Flow in External Magnetic Field • University of Nevada, Reno

  2. 1D-PIC SIMULATION PARAMETER • Plasma • fully ionized hydrogen • plasma length : 4 mm • collision frequency : νce = 2x 108 1/sec • flow velocity usw=4x107 cm/s • External Magnetic Field • profile : • electron gyrofrequency : ωce = 1.76 x 1011 rad/sec @ B = 10 kG • electron gyroradius : re = 16 μm @ B = 10 kG • ion gyroradius : ri = usw/ωci = 0.42cm @ B = 10 kG Computational Parameter mesh size : Δx = 1.426 μm time step : Δt = 4.65 fs total simulation time : 20 ns

  3. TIME EVOLUTION OF ION DENSITY

  4. MAGNETIC FIELD IS PARTIALLY NEUTRALIZED BY SELF-INDUCED FIELD Negative B-field is excited by electrons circular motion at the plasma expansion front.

  5. NEGATIVE ELECTROSTATIC FIELD IS EXCITED AT PLASMA FRONT Ion Expansion Front Since electrons are magnetized, ions go ahead and make a negative sheath field at the plasma front.

  6. ELECTRONS ARE ACCELERATED BY NEGATIVE SHEATH FIELD AND DO CIRCULAR MOTION Figure : Electron phase plot X-px (left) & X-py (right) at t=9.3ns

  7. IONS ARE DECELERATED BY NEGATIVE SHEATH FIELD Figure : Ion phase plot X-Px at 4.6 ns (left) and 9.3 ns (right).

  8. ENERGY SPECTRA SHOW IONS LOSE ENERGY AND ELECTRONS ARE HEATED ~ Flow velocity Te~1.2keV (Initial Te ~ 400eV) Low energy ions increases. Figure : Energy spectrum at t=9.3ns.

  9. SUMMARY OF WHAT’S GOING ON (Assumed the ion energy equals to the sheath potential ) (Assumed the effective collision frequency is the electron cyclotron frequency ) Ions are stopped when they transfer half of their own energy to the electrons Y. Sentoku, K. Mima, P. Kaw, and K. Nishikawa, Phys. Rev. Lett. 90 (2003) 155001

  10. IONS START FLOWING BACKWARD AFTER 10 NSEC

  11. 2D-PIC PARAMETERS Density is normalized by n0=2x1016 ccm ne=2x1016 ccm Te=5keV usw=8x108 (0.0267c) Plasma = 1.8mm x 0.72mm External B-field (Z-direction) 100kG@x=0 - 500kG@x=5.4mm ωce=1.8x1012 rad/sec @B=100kG re=20μm@B=100kG Δx=3.6μm Lx=7.1mm, Ly=1.8mm 200kG

  12. TIME EVOLUTION OF ION DENSITY t=120 ps t=240 ps t=360 ps

  13. TIME EVOLUTION OF ELECTRON DENSITY t=120 ps t=240 ps t=360 ps

  14. FIELD STRUCTURE AT T=60ps Bz = 0.0002 ~20kG Bz @ t=60ps Ex = 0.0002 ~5.8 V/m Ex @ t=60ps Ey @ t=60ps

  15. FIELD STRUCTURE AT T=175ps Bz @ t=175ps Ex @ t=175ps Ey @ t=175ps

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