Single and double probes are simple and common tools for plasma measurements. In the case of nonstationary plasmas, the values of the plasma density obtained with these tools may differ significantly from the correct values measured, e.g., by microwave methods. The reason for such discrepancy could be the Bohm criterion failure during the plasma transition to the steady state. Indeed, the Bohm criterion, which is commonly used as a boundary condition at the plasma-sheath edge, directly determines the ion saturation current to the probe surface. The transition-time duration is studied and explained quantitatively for various plasmas produced by a version of a ferroinductor-coupled plasma source, which has its magnetic core fully immersed in the plasma. Corresponding conversion factors for probe measurements have been evaluated. Also, the influence of a certain amount of “hot” non-Maxwellian electrons on probe characteristics has been investigated.
Surface plasmon-polaritons can be efficiently excited on a plasma-vacuum interface by an electromagnetic wave when a subwavelength diffraction grating is placed in front of the plasma boundary. The excitation efficiency depends strongly on the wave frequency (or plasma density, when the frequency is fixed) and polarization.We show both experimentally and theoretically that this sensitivity can be essentially suppressed. A non-zero angle of incidence and an axially-symmetric diffraction grating ensure near-total absorption of the incident wave in a broad range of wave frequencies (or plasma densities, when the frequency is fixed). Direct detection of surface plasmon-polaritons has been achieved for the first time using a miniature antenna imbedded in the plasma. A new absorption mechanism which is not associated with surface plasma waves excitation is revealed.
We describe the phenomenon of plasma uniformity enhancement in the recently developed simple version of the ferromagnetic inductor coupled plasma source in which a single thin ferromagnetic core having a large diameter (ferroinductor) was fully immersed in plasma. The plasma appeared due to the gas discharge driven by a comparatively low ac voltage ( 350 V) applied to the primary winding of this core. Under certain circumstances the plasma nonuniformity did not exceed a few per cent in the radial direction as well as in the axial direction while the plasma density reached almost 10 13 cm −3 . A qualitative explanation of such uniformity enhancement is suggested.
An experimental study of the recently developed version of the ferromagnetic inductively coupled plasma source has shown that under certain circumstances its input impedance becomes almost independent of the delivered rf driving power and (therefore) of the produced plasma density. This plasma source consists of a large ferromagnetic core, which is fully immersed in plasma. This core is surrounded by a primary winding and plasma appears due to gas discharge driven by an rf voltage applied to this primary winding. We have found values of parameters which determine the input impedance in such an “independent” regime and derived a quantitative theory which is in good agreement with the measured impedance values.
A study of how hydrostatic pressure of up to 13 kbar affects the superconducting transition and electrical resistivity of D-intercalated 2H-NbSe2 samples, in a temperature range of 4.2–50 K. It is shown that the growth of Tc in the intercalated samples cannot be associated solely with the suppression of the charge density wave (CDW). For a more complete explanation of the effect of increasing Tc, it is necessary to account for changes in the density of the electron states at the Fermi level, not associated with CDW, and also changes in the constants of the electron-phonon coupling, caused by the pressure.
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