Laboratory simulations of astrophysical jets and solar coronal loops: new results

An experimental program underway at Caltech has produced plasmas where the shape is neither xed by the vacuum chamber nor xed by an external coil set, but instead is determined by self-organization. The plasma dynamics is highly reproducible and so can be studied in considerable detail even though the morphology of the plasma is both complex and time-dependent. A surprising result has been the observation that self-collimating MHD-driven plasma jets are ubiquitous and play a fundamental role in the self-organization. The jets can be considered lab-scale simulations of astrophysical jets and in addition are intimately related to solar coronal loops. The jets are driven by the combination of the axial component of the J B force and the axial pressure gradient resulting from the non-uniform pinch force associated with the ared axial current density. Behavior is consistent with a model showing that collimation results from axial non-uniformity of the jet velocity. In particular, ow stagnation in the jet frame compresses frozen-in azimuthal magnetic ux, squeezes together toroidal magnetic eld lines, thereby amplifying the embedded toroidal magnetic eld, enhancing the pinch force, and hence causing collimation of the jet.