Neutral gas density depletion due to neutral gas heating and pressure balance in an inductively coupled plasma

Abstract

The spatial distribution of neutral gas temperature and total pressure have been measured for pure N 2 , He/5%N 2 and Ar/5%N 2 in an inductively coupled plasma (ICP) reactor, and a significant rise in the neutral gas temperature has been observed. When thermal transpiration is used to correct total pressure measurements, the total pressure remains constant regardless of the plasma condition. Neutral pressure is depleted due to the pressure balance when the plasma pressure (mainly electron pressure) becomes comparable to the neutral pressure in high density plasma. Since the neutral gas follows the ideal gas law, the neutral gas density profile was obtained from the neutral gas temperature and the corrected neutral pressure measurements. The results show that the neutral gas density at the centre of the plasma chamber (factor of 2-4×) decreases significantly in the presence of a plasma discharge. Significant spatial variation in neutral gas uniformity occurs in such plasmas due to neutral gas heating and pressure balance.

Direct measurements of neutral density depletion by two-photon absorption laser-induced fluorescence spectroscopy

“…Finally, the neutral density has been recently obtained from the total neutral pressure measured by a manometer in combination with optical measurements of the rotational neutral temperature and significant neutral depletion was measured coincidental with neutral gas heating. 11 In this letter, we present measurements of neutral gas depletion obtained by direct measurement of the ground state neutral gas density. The neutral gas density ͑xenon atoms͒ is obtained by spatially resolved laser induced fluorescence spectroscopy with two-photon excitation ͑TALIF͒.…”

“…A number of experimental studies in high density magnetized plasmas have suggested significant neutral gas heating with temperatures in agreement with the above estimate. 3,11,16 Secondly, one should incorporate the magnetic pressure in the overall pressure balance.…”

Observations of neutral depletion and plasma acceleration in a flowing high-power argon helicon plasma

“…1 Direct measurements of neutral pressure with probes along the axis of an argon helicon plasma showed significant neutral depletion in the center of the discharge. 8 Additionally, computational simulations have been performed to model neutral transport and depletion. 3 Miljak et al observed a density maximum in a high-power, double-antenna helicon discharge attributed to neutral depletion.…”

Effect of helium on spatial plasma parameters in low pressure argon-helium plasma

“…Gas heating is an important issue in the analysis of plasma behavior, and it has been studied elsewhere. 22,23 When an electron experiences the momentum transfer collision with a neutral atom, the electron losses only small amount of its kinetic energy in proportion to their mass ratio. Due to the light mass of helium, the helium gas is heated better by the electrons through the momentum transfer collision.…”