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

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

Experimental Setup and Formation of Current Sheet Experimentally measured flux evolution n e = 1-10 x10 13 cm -3, T e ~5-15 eV, B~ G,

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

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

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

Anatomy of MRX Scaling In the outside of the e- diffusion region, reconnecting field E y is primarily determined by j Hall xB: Collisional resistivity

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

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) Solar Flare Experiment on MRX

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

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

STABLE UNSTABLE Cathode Anode B t = 1.06 kG q<1 q>1 Kink instability B t = 0.36 kG

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

Magnetic Relaxation is observed Taylor State:  ~ constant  Magnetic relaxation RFP toroidal plasmas

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)