Experimental Study of Magnetic Reconnection and Dynamics of Plasma Flare Arc in MRX Masaaki Yamada

1. Experimental Study of Magnetic Reconnection and Dynamics of Plasma Flare Arc in MRX • Masaaki Yamada Center for Magnetic Self-organization PPPL, Princeton University August 3 2009 2009 SHINE Meeting at Nova Scotia In collaboration with E. Oz, J. Xie, D. Lecoanet and H. Ji

2. Recent Progress Experimental study of the reconnection layer on MRX => Fast reconnection in collsionless regime is determined by Hall effects except the e-diffusion regime • Two-scale diffusion region • Thickness of the electron diffusion layer > c/pe • MRX scaling in transition from MHD to 2-fluid regime • New results from our solar flare experiments

3. Experimental Setup and Formation of Current Sheet Experimentally measured flux evolution ne= 1-10 x1013 cm-3, Te~5-15 eV, B~100-500 G,

4. Rectangular shape Collisional regime:mfp < Slow reconnection No Q-P field Neutral sheet Shape in MRX Changes from “Rectangular S-P” type to “Double edge X” shape as collisionality is reduced X-type shape Collisionless regime: mfp > Fast reconnection Q-P field present <= Ma & Bhattacharjee ,’96

5. Fast Reconnection <=> Hall Effects => • Hall Effects create a large E field (except at X point) • e-i collisions ~ small • A major question => What is a scaling law w.r.t. collisionality

6. MRX Scaling:* vs (c/i)/ sp A linkage between space and lab on reconnection Breslau Hall MHD Nomalized by Spitz Yamada et al, PoP, 2006 MRX scaling shows a transition from the MHD to 2 fluid regime based on (c/pi)/ sp

7. Anatomy of MRX Scaling Collisional resistivity In the outside of the e-diffusion region, reconnecting field Ey is primarily determined by jHall xB:

8. MRX Scaling: eff linearly increases with mfp/L Hall effects: Next Step => Add guide field

9. Solar Flare Experiment on MRX Main Objectives (1) To determine stability conditions for a single flux rope as a function of field line twist, q, curvature, and the “strapping”field, (2) To evaluate the effects of line tying for flux rope plasma (3) To measure the magnetic energy transfer to the plasma during magnetic self-organization (eruption)

10. Experimental Setup MRX vacuum vessel Equilibrium Field flare electrodes ` ` Guide Field D a Magnetic probes Guide Field Coils Equilibrium Field Coils D: 2R FLARE Diameter a: Flare radius

11. Electrodes inside the MRX vacuum vessel Flare photos taken with a commercial Canon Powershot 100 µs exposure

12. Kink instability q<1 UNSTABLE • Bt = 0.36 kG Cathode q>1 STABLE • Bt = 1.06 kG Anode

13. Stability Condition for a Partial Arc • R=20, a =7 cm 180o • Electrode angle ~90o 1 • The data shows that the stability condition for a simple toroidal q value without line-tying effects describes the experimental data. • => line-tying effects?

14. Magnetic Relaxation is observed Taylor State:  ~ constant • Magnetic relaxation RFP toroidal plasmas

15. Summary • Hall effects facilitate fast reconnection in MRX • Transition from collisional MHD to two-fluid regime => changes the neutral sheet profile and the reconnection rate • A new scaling found on reconnection rate • A new experimental campaign has started to study the dynamics of solar flares (=> Oz, Poster)