Continuous gas discharge plasma with 200 K electron temperature

Abstract

A very cold and collisional hot-filament discharge plasma is created in a vacuum chamber with an inner wall cooled by liquid nitrogen. The inner chamber ͑16.5 cm diameterϫ 30 cm͒ has two negatively biased tungsten filaments for plasma generation and a Langmuir probe on axis for diagnostic measurements. With the wall at 140 K, 0.5-16 mA filament emission, and 1.6 mTorr carbon monoxide as the working gas, probe data give electron temperatures of 17-28 meV ͑197-325 K͒ with corresponding densities of 10 8 -10 9 cm −3 . With He, Ar, H 2 , and N 2 at 140 K, the electron temperatures are Ͼ500 K. The lower electron temperature with CO is attributed to the asymmetric CO molecule having a larger cross section for electron excitation of rotational modes as a consequence of its dipole moment.

Plasma Parameters of a Gliding Arc Jet at Atmospheric Pressure Obtained by a Line-Ratio Method

“…But plasma parameters of the gliding arc in a non-equilibrium state are discussed only qualitatively or estimated indirectly by other parameters such as current density [16] . In a non-equilibrium state, plasma parameters can be measured by a Langmuir probe [17] , microwave interferometer [18] , laser Thomson scattering [19] and optical emission spectroscopy (OES) [20] . The OES technique, however, is a more appropriate method at atmospheric pressure due to its advantages of being non-intrusive, inexpensive and convenient.…”

Low-dimensional structures in a complex cryogenic plasma

“…In experiments, ultracold plasma was produced by photoionizing laser-cooled xenon atoms [5]. A hot-filament discharge plasma was created in a vacuum chamber with an inner wall cooled by liquid nitrogen [20]. We produced cryogenic plasma by applying high voltage between needles in a gas cooled by liquid helium [7,9] where the plasma disappeared in a few seconds in a gas with 4 K electron temperature, or by applying high voltage between needles in liquid helium [8], where plasma disappeared in microseconds.…”

“…while recent advances in cryogenic plasma challenge the basic understanding of plasmas [2][3][4][5][6].…”

A magnetized plasma with very low electron temperature

“…Under the optimal conditions for cold electrons, the electron temperature is 0.017 eV (198 K), the electron density is 1.8 × 10 8 cm −3 , the electron Debye length is 72 µm, the ion Debye length is 46 µm, the electron-ion collision frequency is 3.6 × 10 6 s −1 , and the electron cyclotron frequency is 5.8 × 10 8 s −1 . Comparable electron temperatures and densities had previously been achieved in a hot-filament discharge device without a magnetic field [8]. In both devices, the CO pressure required for cooling is several mTorr.…”

“…Recently, an unmagnetized hot-filament discharge plasma was created in which the electron temperature was sufficiently low for the electron-ion mean free path to be smaller than the dimensions of the device and also smaller than the electronneutral mean free path [8]. The low electron temperature was obtained by creating the plasma in CO gas cooled to 80 K. The neutral CO gas is an effective cooling agent for electrons because it has a dipole moment that decreases the mean free path for energy transfer.…”