We describe electron temperature measurements in the SSX MHD wind tunnel using two different methods. First, we estimate Te along a chord by measuring the ratio of the CIII 97.7 nm to CIV 155 nm line intensities using a vacuum ultraviolet monochrometer. Second, we record a biasing scan to a double Langmuir probe to obtain a local measurement of Te. The aim of these studies is to increase the Taylor state lifetime, primarily by increasing the electron temperature. Also, a model is proposed to predict magnetic lifetime of relaxed states and is found of predict the lifetime satisfactorily. Furthermore, we find that proton cooling can be explained by equilibration with the electrons.
We describe ion and electron temperature measurements in the Swarthmore Spheromak Experiment (SSX) MHD wind tunnel with the goal of understanding limitations on the lifetime of our Taylor-state plasma. A simple model based on the equilibrium eigenvalue and Spitzer resistivity predicted the lifetime satisfactorily during the first phase of the plasma evolution. We measured an average T e along a chord by taking the ratio of the C I I I 97.7 nm to C I V 155 nm line intensities using a vacuum ultraviolet (VUV) monochromator. We also recorded local measurements of T e and n e using a double Langmuir probe in order to inform our interpretation of the VUV data. Our results indicated that the plasma decayed inductively during a large part of the evolution. Ion Doppler spectroscopy measurements suggested that ions cooled more slowly than would be expected from thermal equilibration with the electrons, which maintained a constant temperature throughout the lifetime of the plasma.
We describe experiments and simulations of dynamical merging with two Taylor state plasmas in the SSX device. Taylor states are formed by magnetized plasma guns at opposite ends of the device. We have performed experiments with Taylor states of either sense of magnetic helicity (right-handed twist or left-handed twist). We present results of both counter-helicity merging (one side left-handed, the other right-handed) and co-helicity merging (both sides left-handed). Experiments show significant ion heating, consistent with magnetic reconnection. Magnetohydrodynamic simulations of these experiments reveal the structure of the final relaxed, merged state.
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