1. Multiscale Turbulence excited by a pulsed current sheet Walter Gekelman,Stephen Vincena, Patrick Pribyl, Brett Jacobs, Eric Lawrence (UCLA Department of Physics and Astronomy), Paul Kintner (Cornell University,Dept. of Engineering) Franklin Chiang (UCLA Dept of Engineering) Noam Katz (Physics Dept, MIT)

2. Narrow Current sheets occur in many situations Current sheet Ion flow Reconnection experiment Current sheet

3. Cathode discharge plasma Highly Ionized plasmas n ≈ 3 x 10 12 /cm 3 Reproducible, 1Hz operation > 4-month cathode lifetime Up to 2.5kG 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 Operates as a national user facility http://plasma.physics.ucla.edu/ Overview of the experimental device

5. Orientation Making a Narrow Current Channel

7. 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 data collection

8. Density Density Perturbation as seen with Laser Induced Fluorescence

9. Electric Field Probes Challenge; They must be Debye scale in size In space (auroral ionosphere) D is 1- 10 m In LAPD D is 30 microns

10. E Field Probe: Constructed at UCLA MEM’s lab

11. Bond Pads Probe Tips E Field Probe

12. E probe and air-cooled circuit box

13. Circuit diagram (1 probe) Drives 50 Ohm cable

14. Electric field in current channel

15. Field Components

16. Spectra E perp

17. Spectra E parallel

18. Wavelet Analysis E Perpendicular to Background Magnetic Field f ce /2 f pi -in

19. Wavelet Analysis E Parallel to Background Magnetic Field Enhanced HF

20. Probe in electron beam (low density <10 9 cm -3 plasma) B0B0 LaB 6 emitter 3 mm dia 4 tip microprobe e-beam Background Plasma

21. Higher Frequencies- Langmuir Waves The probe response was less than 2 GHz- in a separate experiment at lower density we searched for electron solitary structures. They are Debye scale size entities which move as fast as v te

22. Spiky turbulence Voltage (Volts) Time (ns) V=4X10 7 cm/s V the = 1X10 8 cm/s

24. Conditional Averaging

25. Key issues raised in this experiment 1)Are low frequency phenomena (e.g. Drift Alfvén waves, flows) coupled to high frequency phenomena (lower hybrid, whistlers and Langmuir waves)? 2)What is the electron distribution function f(r,v,t) ? 3)What is the electron (high frequency) physics in a magnetoplasma?

26. Velocity Analyzer Grid Area (Cross Section) Collector electrode (~.2 μm) Polyimide (~15 μm) Repel (~.2μm) Shield (~.2μm) Silicon Substrate

27. Design Parameters Angle of Acceptance (desire less than 10 deg): –2 µm hole, total thickness 30 µm  half angle = 3.82 deg –2.5 µm hole, total thickness 30 µm  half angle = 4.76 deg Exposed area –160x160 array of 4 μm 2 holes, 4 µm between holes. –1 mm x 1 mm head  10.24% open area Current being carried –Expected current density: 1000 mA/cm 2  1x10 -5 mA/μm 2 –160 * 160 * 4 * 1E-5 = 1.024 mA (maximum collected) Gap closing force –For g = 15 µm @ 25 V: F ≈ 10 µN