Experimental Studies of the Hall Effect in MRX

Experimental Studies of the Hall Effect in MRX

Y. Ren, S. Gerhardt , A. Kuritsyn, H. Ji, R. Kulsrud, M. Yamada

Princeton Plasma Physics Laboratory

Outline

• The Hall effect in numerical simulation and space observations.

• Experimental study of the Hall effects during magnetic reconnection in the MRX.

• Summary

Magnetic Reconnection in Space and Laboratory

Two Models to Fast Magnetic Reconnection

Generalized Sweet-Parker model with anomalous resistivity.

Two-fluid MHD model in which electrons and ions decouple within the scale of order c/pi

and the reconnection rate is enhanced by the dispersive nature of the whistler wave.

The Hall Effects During Reconnection Shown in 2D Simulations

The out-of-plane magnetic field is generated during reconnection.

P. L. Pritchett, JGR 2001

Different motions of ions and electrons show the decoupling of them, thus generating the in-plane Hall current and the out-of-plane magnetic field.

Space observation showing signs of the Hall effects

The out-of-plane magnetic field.

F.S. Mozer et al., P.R.L. 2002

Can the Hall effects be observed in a laboratory plasma?

MRX-Upgraded

Experimental Setup

90-channel Probe Array Scan( R=1cm, Z=4cm)

Y. Ren et al., PRL 2005

Comparison with numerical simulation (I)

4.8 c/pi

0.9 c/pi

Pritchett, JGR , 2001

Fine structure probe array

• A magnetic probe array with spatial resolution up to 1.25 mm and 71 channels is used to search for the signs of the Hall effects.

Fine structure probe

The Construction of the Fine Structure Probe (I)

The coils are hand-winded with 48 AWG magnet wire to 160 turns and approximately 1mm in diameter and 2 mm in length.

D. Cylinder

The small coils are glued to an alumina rod.

The Construction of the Fine Structure Probe (II)

Aluminized mylar is used to provide electrostatic shielding. The 3dB point of the frequency response is about 1MHz.

Fine structure probe

The probe location• The fine structure probe is inserted in the radial direction in the MRX

at two locations, Z=7cm and Z=-7cm, are extensively studied.71-channel magnetic probe array

The toroidal field reversal is found in both locations

(1)

(2)

(3)

Comparison with numerical simulation (II)

71-channel probe location Pritchett, JGR , 2001

1.8 c/pi

(1)

VZe/VA» 0.7

(underestimate VZe)

(2) Ve/VA» 1.2 in numerical simulation

Electron

Ion

The Effect of collisionality on the Hall Effect

Working gas: D2

Quadrupole field in Argon Plasma

pic ~14 cm, assuming Z=1Fill pressure 2.1 mTor.

~0.3, ~90ZHall BB mfp

Summary

• The Hall effects are observed during magnetic reconnection in MRX. Good agreement is found between experiment and simulation.

• The future goal is to study the relation between the Hall effect and fluctuations and to study the quadrupole field with fine magnetic probe array.