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Spontaneous onset of magnetic reconnection in toroidal plasma caused by breaking of 2D symmetry
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View: Figures


Image of FIG. 1.
FIG. 1.

(Color) Illustration of the poloidal magnetic field configurations applied in VTF. In (a), the poloidal field coils are located outside the vessel yielding an open cusp configuration where the field lines intersect the vacuum vessel walls. In (b), the closed cusp configuration is produced by in-vessel coils such that the field lines are confined in the experiment.

Image of FIG. 2.
FIG. 2.

(Color) (a) and (b) Measured contours of plasma current, and electrostatic potential during the initial phase of the forced reconnection pulse. Each column of subfigures corresponds to a snapshot in time as indicated at the top. (c) and (d) Total current in the x-line region as measured by a Rogowski coil in an open cusp hydrogen and argon discharge respectively. (e) Set of equations which can account for the oscillatory response observed in 2D reconnection as well as the exponentially growing reconnection rate in 3D reconnection events. (f) Plasma current recorded as a function of time in the x-line region at two separate toroidal locations during a 3D reconnection event in the closed cusp configuration. (g) The reconnection electric field pulses at the same toroidal cross sections considered in (f).

Image of FIG. 3.
FIG. 3.

(Color) (a) Illustration of the system of currents driven by time variations in φ. The ion-polarization currents j and field-aligned electron currents form closed current loops. (b) and (c) Experimental and theoretical toroidal current profiles driven by changes in φ.

Image of FIG. 4.
FIG. 4.

(Color) Measured contours of the plasma density and the reconnection rate. The measurements were obtained in a 55 μs time interval centered about a spontaneous reconnection event.

Image of FIG. 5.
FIG. 5.

(Color) (a) Inductive (reconnection) electric field measured at the mid-plane of the VTF at the onset of spontaneous reconnection. (b) q-profile for a typical VTF discharge; in the shared flux region yields spontaneous reconnection events. (c) Electrostatic in-plane potential measured at various toroidal cross-sections (as indicated by the red lines in (a)). In the region where the potential rotates with the magnetic field lines.

Image of FIG. 6.
FIG. 6.

(Color) (a) Potential model, φ fitted from the experimental data with the gray magnetic-field line, which passes by the x-line near the onset location (ϕ = 0). (b) divergence of ion polarization currents . (c) experimentally measured change in j || during the 8 μs leading up to peak reconnection. (d) integration of (b) along field lines which gives an asymmetric parallel current similar to that experimentally observed. (e) Measured reconnection electric field as a function of time. The early behavior is well approximated by an exponential fit with γ = 21 μs.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Spontaneous onset of magnetic reconnection in toroidal plasma caused by breaking of 2D symmetry