Plasma flow processes within magnetic nozzle configurations

The acceleration of plasma flow from a static source through confining and guiding expansion magnetic fields has been studied experimentally and numerically. Plasma with 1016 cm3 and 20 eV produced in a 50-cm-long coil with 3.81-cm-radius discharge tube was confined within 23 kG magnetic fields. The transient flow from the ends was studied with spectroscopy, Thomson scattering, pressure probes, and magnetic probes. The flow was axisymmetric, with a throat being formed near the end of the coil, and flow became supersonic in the expanding "magnetic nozzle" geometry. Axial variations of electron density, temperature, and plasma radius were measured. From reduced data, velocity was seen to increase in the flow direction, choking at sonic and magnetic cusp speeds following several microseconds of transients. A two-dimensional MHD numerical model which included all flow and dissipative effects was developed. With a radial parabolic profile of electron density, variation of properties in the axial direction was predicted. Generally, the flow was influenced by electromagnetic interaction and did not behave isentropically. In comparison of the computational predictions with experimentidentified nonclassical transport, electrical resistivity (and conductivity) did follow classical behavior but electron thermal transport was enhanced by a factor as much as 11 times that of classical behavior.