# Presentation: 526702

## Experimental Study Plans of MRX for 

**Two-Fluid Physics of Magnetic Reconnection  **

**Masaaki Yamada**

***August 12 2005***
*** ***

## Outline

**-   Highlight the recent measurements of two-fluid effects seen in MRX and compare them with space observations**
**2 fluid effects observed in local reconnection physics studies to date**
**Current sheet profiles with high resolution (********x ~ c/********pe****)**
**    ****[=> Harris sheet + Quadrupole]**
**Hall Effects [Out-of-plane quadrupole field+Fluctuations]**
**    **_**How to make a combined pictures**_
**Pressure tensor term **
**Comparison with space observations**
**Polar satellite results with out of plane quadrupole field**

## Two competing models to explain fast local reconnection 

**Dedicated lab experiments [LLPD(****EMHD****), MRX, SSX, TS-3, VTF etc.]**

- Generalized Sweet-Parker model

- Petschek-type Model

## A wide array of magnetic probes allow reconstruction of the reconnecting current sheet

- Profile of the neutral sheet has been measured;
-  ~ 0.4 c/pi.

- New fine structure probe
- 71 channels

## A force balance observed in the MRX shows an effect of Hall  MHD term

- A force balance in incoming (x) direction would give;
- 	Jy x Bz = px
- or  [p + Bz2]/20 ~ const.

- Generalized Ohm’s law:

- Phys. Plasmas, v. 7, 1781 (2000)

## Hall term should play a major role in force balance in y direction (Breslau)

- =210-3;	=10-2;		c/pi=2.27710-2

*E* + *v*  *B*

*(j*  *B)/n**e**e*

***j*

- =

- +

## Very Fast Electron Flow

- =210-3;	=10-2;		c/pi=2.27710-2

- flux contours

- separatrix

- ion flow

- electron flow

- symmetry axes

- Max ion speed is 1.084 vA at
-  (.464, 0) and (.735, 0).

- Max electron speed is 3.302 vA at
-  (.562, 0) and (.631, 0).

- Breslau

## Out-of-plane Quadrupole has been predicted by numerical simulations

- By

- Bz

- x/di

- From Drake et al.

- Bz

- By

- By

##  cpi 

- 5 cm

-  cpi
- ≈ 2-10 cm.
-  cpe
- ≈ .5-2.5 mm.

- 1.25 mm

## Toroidal quadupole field is found in off axis locations demonstrating 2 Fluid MHD effects

- Probe at
- z = -7 cm

- Probe at
- z = +7 cm

**Fine Structure Probe [∆ =1mm]**

- R

## 2-D display of Hall toroidal field contours (in colors)with reconnecting field vectors( x=4cm,  z=1cm)  

- Movie is available

## Experimentally measured 3-D field line features in MRX

- Manifestation of Hall effects in MRX
- Electrons would pull magnetic field lines with their flow

## Measured Off-Center Reconnecting Magnetic Field and simulation result

- Bz

-  r/di

## Self-made quadru-pole field size versus fill pressure Collisions reduce the Hall effects

- Bz is the shoulder value of reconnecting field.

## Hall Term is dominant in most of the reconnection experiments  

- Generalized Ohm’s law

- >> 1

**MRX scaling of reconnection rate**
**w.r.t. Normalized ion skin depth**

**How do 2-fluid effects come into play?**

- Breslau

## Measured resistivity scales with regard to system size

- Recent observation from Kuritsyn et al,   d  L

| System |  L (cm) | B (G) | di= c/pi(cm) | sp (cm) | di/ sp |
| --- | --- | --- | --- | --- | --- |
| MRX/TS-3/SSX | 10  | 100-500 | 1-5 | 0.1-5 | .2-100 |
| RFP/Tokamak |       30/100 |   103/ 104 |       10 | 0.1 | 100 |
| Magnetosphere |         109 |  10-3 |       107 | 104 | 1000 |
| Solar flare  |         109 |      100 |       104 | 102 | 100 |
| ISM | 1018 |  10-6 |      107 | 1010 | 0.001 |
|      Proto-star                   di/ s >> 1                          |  |  |  |  |  |

**Linkage between space and lab scales on reconnection**

- Indicates importance of 2-fluid effects

## Push reconnection (merging) experiment in MRX

- Push reconnection involves toroidal (out-of-plane) field.
- 	→ Two cases of counter helicity exist.
- 		Counter helicity	・・・・	Normal ’+-’
- 					Flipped ‘-+’

## Flux plots (‘Normal’ counter helicity)

- Bt<Br

- Bt~Br

- X-point is pushed in when strong Bt comes.

## Flux plots (‘Flipped’ counter helicity)

- Bt<Br

- Bt~Br

- X-point is pushed out when strong Bt comes.

## Interpretation of this phenomena(a) deference of X-point position @250sec 

- A simple two fluids model in which field line is frozen in
- electron fluids explains these observations well.

## Is flux plot reliable?

- Direct evidence may be preferable because flux plot is somewhat artificial.

- 1d probe measurement shows a good agreement with the model
- (or flux plot).

## 1d plot signal during merging

- Same trend is observed during merging, although reproducibility and axisymmetry are not good (flux plot is not available).
-  (These shots were taken by Alex for IDSP measurement.)
- Here, 290sec is the time when radial ion flow becomes largest for ‘Normal’ case.

## New measurement – push probe

- New push probe may bring detailed shape of current  sheet (V- or ^-shape) or quadrupole structure  in early reconnection phase.
- +
- ・Existing 1d probe
- ・Chord-averaged
-   spectroscopy or IDSP
- may be enough to verify or modify the two fluid model?