UAH The Spinning Terrella Experiment Lab Analog for

UAH The Spinning Terrella Experiment: Lab Analog for Earth's Magnetosphere Robert Sheldon 1, Eric Reynolds 2 1 National Space Science and Technology Center, 2 West Virginia University May 30, 2001

Why do we need global pix? UAH �Chapman & Ferraro [1932] wanted the neutral plasma from the sun to produce a "ring current" as it envoloped the Earth. This current was needed to explain Dst. But they didn't know how. �Alfven tried electric fields [1952? ] and failed. �Finally Fred Singer [1957] realized that dipoles trap charged particles which carry a current via the grad-B drift. �If they had taken Birkeland's apparatus [1910] and applied a 400 V DC bias, this is what they would have seen:

Ring Current in the Lab 1) N & e 2) Saturated 3) -400 VDC 4) 0. 5 Tesla 5)10 -200 m. T UAH

UAH Spinning Terrella Experiment �Bell jar, oil roughing pump, HV power supply, Nd-B ceramic magnet �Needle valve used to control the pressure from 10 -400 m. Torr �Langmuir � 2 ports �Webcam �~$10 k

The Distorted Dipole -But the Earth is NOT a simple dipole, it is distorted by the Solar Wind. - The SW acts as a "superconductor" which prevents B-normal across the separatrix. -This is equivalent to an "image" dipole from elementary electrostatics. -Chapman 32, and Parker 61 simulated this distortion as an image dipole "reflected" by the magnetopause. UAH

UAH The Double Dipole M'sphere � Chapman & Ferraro 1932 � Parker 1961 used the double dipole model to explain geomagnetic storms �Laboratory plasmas can easily be set up which are topologically equivalent to Earth's M'sphere �any space effects are topological, no M microphysical Global dynamics and imaging is easily � accomplished

2 Terrella �Two Nd-B-Fe magnets, on alumina standoffs. �We vary the orientation of the magnets, the aspect ratio of the magnets, and the voltage of the magnets. �Glow discharges at 10 -200 m. Torr = m. f. p 0. 3 - 6 mm �The smallest dimension of the glow is 1 -10 mfp UAH

Parallel Dipoles @ High P UAH -High latitude minimum, and Shabansky orbits -Bistable distributions - Quadrupolar regions of magnetosphere are important for trapping and feeding dipole.

Parallel Dipoles @ Low P -Assymetries are caused by 2 -dipoles. -Possibly due to separatrix of grad-B and Ex. B drifts. -This leads to closed orbits that do not encircle the central magnet, "banana orbits", which only occur at narrow range of Voltages at low pressure -Region between the dipoles has compressed fields & appears brighter UAH

Plasma Entry @ Cusps UAH -One magnet grounded, other biassed -Plasma generated by electrons on one magnet, feed into other trapping field due to diffusion though "x-line" -Like northward Bz, this feeding happens at the cusps -The cusps themselves hold the plasma long enough to glow, "Sheldon orbits"

Anti-Parallel Merging UAH -Left magnet grounded, right magnet w/ increasing bias -X-line plasma merging -Isotropization at min-B

Quadrupoles and Merging UAH -Balanced voltages -Appearance of trapped plasma above and below the null point. - These orbits are quadrupolar trapped (drifting around a minima) -Is there a Earth analog?

Aurora & Substorm UAH -Left magnet biassed +10 -60 V -Aurora appears above magnet, and with ion colors -Substorm!

Conclusions (//) UAH �We can learn a great deal from laboratory analogs of the Earth's magnetosphere. Terrella experiments are not just history! �Separation of charge species observed in the lab, suggesting space-charge and field-aligned potentials are possible at Earth. (See poster) �Quadrupole trapping appears in anti-merging geometries, supporting Sheldon-Shabansky orbits �Cusps appear to be entry location for plasma, supporting "sash" theories �"Banana" orbits appear important for narrow voltage regimes --is this a feature in storm development?

Conclusions (anti-//) UAH �Merging X-line geometry is entry point for plasma, supporting reconnection theories �Isotropization of the population is observed at Xline as well, with consequences for the footpoint. �"Balanced" voltages at 2 -dipole X-line generates a unique quadrupolar trap. Is there any evidence for this trap in space plasmas? �Substorm like features can be generated in the laboratory. Can we use these auroral dynamics to probe parent population?

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