RESUMEN
A small RF signal is applied to the anode of a low pressure (P ≤ 200 mTorr), low temperature (T e ≤ 3 eV) direct current (DC) glow discharge operating at an electron density of n e â¼ 106 cm-3. The discharge is modeled as a collection of capacitive, resistive, and inductive circuit elements that have resonances at particular frequencies, much like an RLC circuit. The location of these resonances in frequency space provides information about the plasma parameters. In this work, an electrode that is used to sustain a DC glow discharge is also used to probe the impedance of the discharge. The benefit of this approach is that it is not necessary to insert a physical probe that could introduce perturbations or contaminate the discharge. Experiments were performed to demonstrate this non-invasive impedance probing method for extracting the plasma discharge density at various neutral gas pressures and discharge voltages and currents from changes to the input impedance of the anode. Comparisons between densities extracted with this method and Langmuir probe measurements showed overall good agreement.
RESUMEN
We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 × 10(-6) times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59°), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth's plasma environment.
RESUMEN
An array of highly miniaturized electrostatic lenses is shown to be a viable replacement for meshes or screens in a retarding potential analyzer (RPA) where mechanical ruggedness or the ability to intercept large currents of energetic particles is desirable. Data from a prototype device are presented cross-calibrated with a traditional planar RPA indicating how the so-called microarray configuration avoids energy-dependent transparency (either reduced or enhanced) associated with meshes or screens while providing accurate energy analysis with reasonable energy resolution. In contrast, another ruggedized configuration employing a screen is presented, showing the severity of energy-dependent enhanced transparency, verified by numerical simulation.
RESUMEN
The Auburn Linear EXperiment for Instability Studies (ALEXIS) is a laboratory plasma physics experiment used to study spatially inhomogeneous flows in a magnetized cylindrical plasma column that are driven by crossed electric (E) and magnetic (B) fields. ALEXIS was recently upgraded to include a small, secondary plasma source for a new dual source, interpenetrating plasma experiment. Using two plasma sources allows for highly localized electric fields to be made at the boundary of the two plasmas, inducing strong E × B velocity shear in the plasma, which can give rise to a regime of instabilities that have not previously been studied in ALEXIS. The dual plasma configuration makes it possible to have independent control over the velocity shear and the density gradient. This paper discusses the recent addition of the secondary plasma source to ALEXIS, as well as the plasma diagnostics used to measure electric fields and electron densities.
RESUMEN
Laboratory observations of electromagnetic ion-cyclotron waves generated by a localized transverse dc electric field are reported. Experiments indicate that these waves result from a strong E×B flow inhomogeneity in a mildly collisional plasma with subcritical magnetic field-aligned current. The wave amplitude scales with the magnitude of the applied radial dc electric field. The electromagnetic signatures become stronger with increasing plasma ß, and the radial extent of the power is larger than that of the electrostatic counterpart. Near-Earth space weather implications of the results are discussed.