1. Flows and Instabilities Associated with an Extremely Narrow Current Sheet Presented by Stephen Vincena April 20, 2004 University of Maryland Second Workshop on Thin Current Sheets Collaborators: Walter Gekelman and Patrick Pribyl University of California, Los Angeles Large Plasma Device Laboratory DOE/NSF Basic Plasma Science Facility

2. Cathode discharge plasma Highly Ionized plasmas n ≈ 3 x 10 12 /cm 3 Reproducible, 1Hz operation > 4-month cathode lifetime Up to 3.5kG DC Magnetic Field on axis Plasma column up to 2000R ci across diameter Over 450 Access ports, with 50 ball joints Computer Controlled Data Acquisition Microwave Interferometers Laser-Induced Fluorescence Large variety of probes Now a national user facility http://plasma.physics.ucla.edu/ Overview of the experimental device

3. Electron current sheet generation with ‘Slot’ Cu plate: Length: 18cm=0.6  i, 45  e or  i Width: 1.9cm, 5  e or  i Thickness: 0.15, 0.4  e or  i, 13  e Glass-covered Copper rod 3/8” stainless Steel shaft epoxy

4. Probes: 3-axis, differentially wound magnetic induction probes for fluctuating magnetic fields. Langmuir probes biased to collection ion saturation current yields (assuming Te fixed) density fluctuations when calibrated with a microwave interferometer. Multi-sided Langmuir probes (Mach probes) for ion flow. Example: 1.2mm 4-sided mach probe Tungsten faces

5. Fixed magnetic probe Current sheet antenna  x =2mm Movable flow probe Fixed flow probe Transistor switch capacitors Current = 70A Voltage = 75 V He, B=500G…1.5 kG Photograph T shutter = 1  s View down axis of machine Geometry and Philosophy of data collection

6. Electron current drawn by slot Amperes/10 t/ (L/vA), L=20m

7. y (cm) x (cm) Mach number +0.05 -0.25 Movie of Parallel Ion Flow in a Perpendicular Plane R ci = 4.1 mm  = 3.8 mm y x z, B This movie is available at http://plasma.physics.ucla.edu/bap sf/vincena/umd04/movie1.avi http://plasma.physics.ucla.edu/bap sf/vincena/umd04/movie1.avi

8. Time of peak flow y (cm) x (cm) Mach number +0.05 -0.25 T=690  sec Parallel Ion Flow in a Perpendicular Plane R ci = 4.1 mm  = 3.8 mm

9. Parallel Ion Flow in a Perpendicular Plane y (cm) x (cm) Mach number +0.05 -0.25 T=1000  sec Time during spontaneous fluctuations

10. Peak parallel ion flow at times of maximum density gradient Fluctuations (Drift-Alfven waves) and peak current associated with relatively filled-in density profiles->cross-field transport x/  i Density (/cc)

11. Parallel Ion Flow in a Perpendicular Plane y (cm) x (cm) Mach number +0.05 -0.25 T=1000  sec Time during spontaneous fluctuations Correlation Measurements are Made in this Region

12. Density Fluctuations Due to Drift Waves +10 -10 Frequency: 0.2Fci y (cm) x (cm) This movie is available at http://plasma.physics.ucla.edu/bapsf/vinc ena/umd04/movie2.avi http://plasma.physics.ucla.edu/bapsf/vinc ena/umd04/movie2.avi

13. x/  i Density Parallel ion flow (V z /C s ) Perpendicular ion flow (V y /C s ) M-par M-perp #/cc

15. Time Series (Bx) FFT frequency (Hz) arb units x=0, y=0 (center) He, B = 500 G 3 axis magnetic probe inside current sheet Spontaneous fluctuations

16. Coherency Spectrum x (cm) m : movable probe f = fixed probe  z =2.24 m

17. First glimpse of electron solitary structures ? 1 Ghz amplifier Probe tip 12  X 27  To 4 GHz digitizer

18. Summary & Future work Observed strong parallel ion flows associated with a thin electron current sheet This flow is periodically disrupted by the formation of steep density gradients and the onset of drift wave turbulence. Building 3D mm-scale mach probe. Independently measure perpendicular ion flow using laser-induced fluorescence. Developing micro-scale electric field probes to study fine-scale (Debeye-length) electron structures (electron phase space holes) within the current sheet. Quantitative, scaled comparisons with drift wave theory and numerical predictions.