Bob Merlino University of Iowa N. D’Angelo, B. Kustom, D. Susczynsky, S. Cartier, J. Willig

1. Laboratory studies of the effects of electron and ion neutral collisions on electrostatic plasma waves Bob Merlino University of Iowa N. D’Angelo, B. Kustom, D. Susczynsky, S. Cartier, J. Willig APS DPP Orlando, FL 2002

2. Outline • The Farley-Buneman Instability • The electrostatic ion-cyclotron instability • The D’Angelo Instability ( Kelvin Helmholtz, parallel velocity shear instability)

4. Auroral Electrojet • Large horizontal currentsthat flow in the D and Eregions of the ionosphere • Remarkable for theirstrength and persistence • Responsible for type Iirregularities observed by radar backscatter

5. Equitorial Electrojet • currents driven by E  B drifts • ions held back since • electrons drift since • if ve > Cs longitudinal plasma waves grow that travel  to B

7. Laboratory Experiment on the Farley Buneman Instability

8. E E Farley Buneman –results Spectrum of oscillations

9. Electrostatic Ion Cyclotron Waves Lab Space

10. Current Oscillations due to EIC Instability

11. EIC waves in the diffuse aurora • Oxygen-cyclotron emissions detected on sounding rocket (Bering, 1983) down to altitudes of 120 km. • EIC fluctuations seen in the aurora (Martelli et al). • At these altitudes the ion neutral collision frequency exceeds the oxygen cyclotron frequency. At what level of collisionality will EICwaves be quenched ?

12. Collisional EIC Waves For EIC waves driven by parallel electron currents, analysis* shows that ion collisions are stabilizing (damping) but electroncollisions can be destabilizing (growth) *Satyanarayana, Chaturvedi, Keskinen, Huba, Ossakow (JGR ’85)

13. The Q Machine gas button n ~ 108 – 1010 cm-3 Te = Ti = 0.2 eV

14. Effect of ion-neutral collisions fin = 80 kHz amplitude vs pressure frequency vs pressure

15. Effect of m+/mn ratio Experiments done with K+ and Cs+ ions inneutral gases- He, Ne, Ar, Kr, and Xe For each ion/neutral pair the neutral gas pressure at which wave damping by ion collisions begins to dominate, Pmax is determined by i = Nv, where  is the efficiency of momentum transfer per collision  = 2/(1 + m+/mn).

16. Collisional EICI - Conclusions • EIC waves driven by parallel electron currrents continue to be excited even for ion-neutral collision frequencies: • EICI in the bottomside ionosphere could be a source of transversely accelerated heavy ions which eventually travel to higheraltitudes (magnetospheric heavy ions).

17. y x B The D’Angelo Instability*(Kelvin-Helmholtz in fluid dynamics) cloud rollup vi KH in a plasma: PVSI *also known as the arallel velocity shear instability - PVSI

18. PVSI in Earth’s Polar Cuspand comet tails • Ions flow into the polar cusp along magnetic field lines. • Shear in the ion flow has been observed. • KH turbulence may cause particles to diffuse acrossB • Similar wave motion may occur in comet tailsdue to shear between cometary ions and solar wind

19. Collisional PVSI • F region observations of intense velocity shear and es waves near auroral arcs. • Irregularity scales sizes ( ) down to m’s. • Frequencies < in - ‘collisonal modes’ • Basu & Coppi (BC) (1988) propose collisional PVSI with instability threshold

20. B Shear regions Experiment on collisional PVSI Experiments performed in a double-ended Q machine, using a K+ plasma

21. V PVSI – Experimental Results radial electric potential measurements fluctuation spectrum fluctuation amplitude

22. Collisional damping of PVSI 50% neutral gas pressure (Torr)

23. 1 10 102 103 104 105 Collisional PVSI- comparison with BC theory instability condition: here Te = Ti, so define T then T > 1 for PVSI

24. Conclusions • We have studied the effects of electron and ion-neutral collisions on various electrostatic plasma modes. • Collisions can have decisive consequences for both the excitation and damping of plasma instabilities.