Schematic of the Swarthmore Spheromak experiment showing the orientation of a single spheromak and six of the twelve magnetic probes (the other six are installed in the poloidal plane orthogonal to the one shown). The flux conserver is in diameter and in length. The dipole trapping coil (split) is at the midplane. The poloidal flux surfaces shown within the flux conserver are computed using the EQLFE Grad-Shafronov equilibrium solver.
Global magnetic structure of the dipole trapped spheromak. Five views of the data are shown: two orthogonal projections (top row), three projections (bottom row) at . For comparison, the full data (a) and the axisymmetric component (b) are both shown.
(Color) The average energy in the component (solid lines) exceeds the average energy of the components (dashed lines) for the lifetime of the configuration. The east, midplane, and west are color coded red, green, and blue, respectively.
Ratio of the to 0 mode energies for various currents in the midplane coils. A mostly axisymmetric configuration forms only for total current (solid); final states are dominantly for zero current (dashed) and for or more in the midplane coils (not shown).
Typical line shape (a) at and the time dependence of the line intensity (b), line shift (c), and linewidth (d). The data points in (c) and (d) indicate the results of Gaussian fits to the line shapes, while the solid line indicates values computed from the first and second moments of the line shapes.
Ion temperature averaged over ten externally identical shots for a view chord along a diameter (squares) and for a view chord with impact parameter at (triangles). The latter view chord is insensitive to the expected open flux region and intercepts all of the expected closed flux region.
Impact parameter dependence of flow (a) and ion temperature (b) at two times, when the ion temperature is greatest and during decay of the equilibrium. Data at each chord are averaged over ten externally identical shots and over a window.
Abel inverted emissivity profiles (solid line with shaded error band) at and at . The measured dependence of line strength on impact parameter (data), as well as the Abel integral of the emissivity profile (dashed line), are overlayed for reference.
Radial profiles of (a) and (b). Data are shown for the east, midplane, and west probe locations. The midplane equilibrium model calculations (green) for (long dashed) and (solid) are similar and agree with measurements at large . For reference, the dotted lines indicate the Bessel function model for a spheromak in a cylindrical flux conserver with zero vacuum field.
Radial profile for the broad current profile equilibrium. The shaded region indicates where there are no closed flux surfaces.
Results of 3D MHD simulations. The time evolution of plasma kinetic energy for different Fourier harmonics show decay of the initial perturbation, and demonstrate the stability of the dipole-trapped spheromak configuration with respect to the interchange modes, the tilt mode, as well as co-interchange modes.
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