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Radial Velocity Profiles and Magnetic Field Probes for Hypervelocity Plasma Deflagration Jets

Radial Velocity Profiles and Magnetic Field Probes for Hypervelocity Plasma Deflagration Jets

Thursday, May 24, 2018 at 1:00 pm
LINC 444
Jesse Rodriguez

The fundamental physics of turbulence in plasmas is not well understood. Recent studies of the plasma deflagration accelerator in the High Temperature Gasdynamics Lab at Stanford University have demonstrated the presence of small scale instabilities that limit the lifetime of the Z pinch and are not reproduced by coaxial plasma accelerator simulations. To provide more data to inform these simulations, a radial profile of axial velocity was measured. Magnetic field probes were designed to produce well-behaved results at high frequencies, enabling the use of techniques like wavelet decomposition to identify the fastest-growing instabilities in the flow.

The velocity measurement produced a radial profile of axial velocity that was consistent with prior experimental data and reproduced key features of the simulations. The core of the jet was shown to travel uniformly at an axial velocity of 92 +/-5 km/s out to a radial position of 5 mm, and the shear flow around the jet rose to ~120 km/s at 10 mm. An impurity emission line (Fe I) was used to generate the velocity profile and thus the experiment may have failed to capture features tied specifically to the physical characteristics of the plasma species. The magnetic field probe project produced prototypes that measure axial, azimuthal, and radial field variation. A calibration procedure for the probes was designed and demonstrated. The calibration curve shows the onset of resonances at ~10 MHz, calling for improvements to achieve the desired maximum operating frequency of 100 MHz. The calibration curve also suggests that the probe will produce a signal of order ~1 V during operation, showing that the selected circuit components are sufficient for detection of the fine structure of the magnetic field.