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NO6.00002 Laboratory observations of self-excited dust acoustic shock waves

This study explores the formation and characteristics of self-excited dust acoustic shock waves in a laboratory setting, shedding light on nonlinear wave phenomena and their potential applications. The findings may have implications for phenomena in Saturn's rings and dust molecular clouds. The experiment setup involved a DC glow discharge plasma, with kaolin powder of micron size, and parameters such as Te ≈ 2-3eV, Ti ≈ 0.03eV, and plasma density of ~1014 – 1015m-3. By analyzing the shock amplitude and thickness, the study reveals insights into dust-neutral collisions, dust charge variation effects, and dissipation mechanisms in nonlinear waves. The experiments evidenced the formation and speed of shock waves, providing crucial data for understanding and modeling such phenomena in plasma environments.

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NO6.00002 Laboratory observations of self-excited dust acoustic shock waves

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  1. 51st Annual Meeting of the APS Division of Plasma Physics Atlanta, GA Nov. 2-6, 2009 NO6.00002Laboratory observations of self-excited dust acoustic shock waves R. L. Merlino, J. R. Heinrich, and S.-H. Kim University of Iowa Supported by the U. S. Department of Energy

  2. Linear acoustic waves • Small amplitude, compressional waves obey the linearized continuity and momentum equations • n and u are the perturbed densityand fluid velocity • Solutions: n(x  cst) u(x  cst)

  3. Nonlinear acoustic waves • Solution of these equations, which apply to sound and IA waves (Montgomery 1967) show that compressive pulses steepen as they propagate, as first shown by Stokes (1848) and Poisson (1808). • Now, u and  are not functions of (x  cst), but are functions of [x  (cs + u)t], so that the wave speed depends on wave amplitude. • Nonlinear wave steepening  SHOCKS

  4. t0 t1 t2 t3 Amplitude Position Pulse steepening • A stationary shock is formed if the nonlinearlity is balanced by dissipation • For sound waves, viscosity limits the • shock width

  5. Importance of DASW • Unusual features in Saturn’s rings may be due to dust acoustic waves • DASW may provide trigger to initiate the condensation of small dust grains into larger ones in dust molecular clouds • Since DASW can be imaged with fast video cameras, they may be used as a model system for nonlinear acoustic wave phenomena

  6. side view Plasma Nd:YAG Laser Anode y B x Cylindrical Lens Dust Tray PC Digital Camera top view B x z Experiment •  DC glow discharge plasma •  P ~ 100 mtorr, argon • kaolin powder • size ~ 1 micron •  Te ~ 2-3 eV, Ti ~ 0.03 eV •  plasma density • ~ 1014 – 1015 m-3

  7. No Slit 1 cm slit Slit position 1 Slit position 2 y z Effect of Slit anode 1 cm

  8. SLIT POSITION 1

  9. Confluence of 2 nonlinear DAWs • With slit in position 1, we observed one DAW overtake and consume a slower moving DAW. • This is a characteristic of nonlinear waves.

  10. SLIT POSITION 2

  11. Formation of DA shock waves • When the slit was moved to a position farther from the anode, the nonlinear pulses steepened into shock waves • The pulse evolution was followed with a 500 fps video camera • The scattered light intensity (~ density) is shown at 2 times separated by 6 ms.

  12. Average intensity Formation of DASW Shock Speed: Vs  74 mm/s Estimated DA speed: Cda  60 – 85 mm/s  Vs/Cda ~ 1 (Mach 1)

  13. ndust Position (mm) Theory: Eliasson & ShuklaPhys. Rev. E 69, 067401 (2004) • Nonstationary solutions of fully nonlinear nondispersive DAWs in a dusty plasma

  14. Shock amplitude and thickness • Amplitude falls off roughly linearly with distance • For cylindrical shock, amplitude ~ r 1/2 • Faster falloff may indicate presence of dissipation • Dust-neutral collision frequency ~ 50 s1 • mean-free path ~ 0.05 –1 mm, depending on Td

  15. Limiting shock thickness • Due to dust-neutral collisions • Strong coupling effects(Mamun and Cairns, PRE 79, 055401, 2009) • thickness d ~ nd / Vs, where nd is the dust kinematic viscosity • Kaw and Sen (POP 5, 3552, 1998) givend 20 mm2/s •  d  0.3 mm • Gupta et al (PRE 63, 046406, 2001)suggest that nonadiabatic dust charge variation could provide a collisionless dissipation mechanism

  16. Conclusions

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