Experimental study of energy conversion/transport process during magnetic reconnection in flux tube merging experiments

Abstract:

Here we present recent progress of our experimental study of energy conversion/transport process of magnetic reconnection in our flux tube merging experiments. The driven magnetic reconnection in fusion related high energy facilities demonstrated ion heating in ~0.1keV regime in TS-3, ~1keV both for ions and electrons in MAST and the record is updated to 2.3keV in ST40 based on ΔT_i ∝ B_rec² scaling of reconnection heating. Electrons are typically heated locally (smaller scale length than ion skin depth) around the X-point, while ions are globally heated in the downstream region of outflow jet. Both ion and electron temperature are typically equilibrated in collisional time scale, while each characteristic heating profile is clearly observed in a faster time scale than ion-electron energy relaxation time. Especially, recent U-Tokyo experiment in TS-6 enables detailed full-2D in-situ measurement of both magnetic field and ion temperature profile using ultra high resolution ion Doppler tomography which could resolve detailed structure in gyro-scale (ρ_i~10mm) and clear heating characteristics have been revealed by the advanced plasma diagnostics. During magnetic reconnection, blob-like structure is initially formed in the diffusion region, then is ejected toward downstream and finally forms clear double-peak profile at the end of merging process. The hot spots are typically on the field lines of reconnected flux and transported toward field line direction which is connected to global region surrounding the inflow flux tubes. The ratio of parallel/perpendicular heat conduction is strongly affected by the weight of guide field (gyro frequency) as in κⁱ_///κⁱ_⊥ ~ 2(ω_ciτ_ii)²>>1 and characteristic double-ring structure which surrounds the two merging flux tubes appears through the reconnection process. Such key highlights of recent clear results and achievements from our experimental study will be presented in the conference.