Excessive Balmer line broadening in a plane cathode abnormal glow discharge in hydrogen

Abstract

Results of a Doppler spectroscopy study of the hydrogen Balmer alpha line in an abnormal glow discharge operated in pure hydrogen are reported. Measurements of line shapes are performed side-on to the discharge axis in a low electric field region of negative glow. The excessive Balmer alpha broadening is detected and its presence and linewidth is related to the collisions of fast hydrogen atoms with molecular hydrogen. The collision model enabled also an estimation of effective cross section data from the Balmer alpha axial intensity decay curves. Large excessive Balmer alpha line broadening in pure hydrogen and its dependence upon the direction of observation with respect to the electric field is in contradiction to the resonance transfer model, proposed byMills et al. in several publications [see, e.g., IEEE Trans. Plasma Sci. 31, 338 (2003)].

Collisional kinetics of non-uniform electric field, low-pressure, direct-current discharges in H2

“…For the purposes of this paper the negative glow and the Faraday dark space are lumped together as a region of zero electric field [10]. This figure shows the approximate electrode configuration including a planar cathode and anode [11,12], a planar cathode and a ring anode [11], a planar cathode and a hollow anode [9], a hollow cathode(s) and ring anode(s) [13,14], or a cathode and anode constructed of wire grids [15]. The model places a planar anode at some representative position between the entrance to the hollow anode or the plane of the ring anode and the wall beyond these positions.…”

“…The model will eventually need a better numerical treatment with more realistic geometries and using realistic differential collision cross sections. Thus far, only results using very approximate differential cross sections are available [8,9].…”

Spectroscopic investigation of wave driven microwave plasmas

“…Anomalous, even extreme, hydrogen line broadening was found in a number of mixed discharge plasmas excited via direct current ͑dc͒ or radio frequency ͑rf͒ electric fields. [1][2][3][4][5] The Balmer line spectra emitted by these discharges have typical multimode behavior, with widely broadened "wings" ͑"fast" hydrogen͒ and a sharp top ͑"slow" hydrogen͒. The results have usually been explained in terms of Doppler shift and broadening due to the acceleration of charges ͑such as H + , H 2 + , and H 3 + ions͒ in the high dc electric fields present in the sheath regions of these discharges.…”

Comment on “Water bath calorimetric study of excess heat generation in resonant transfer plasmas” [J. Appl. Phys. 96, 3095 (2004)]

“…[19][20][21] The excess H ␣ line broadening from dc glow discharges in gas mixtures, such as Ar-H 2 , has been explained using the latest sheath-collision model in which the energy source is the applied voltage. 20,22 Reference 1 cites Mills et al 3 as evidence that the sheath-collision model fails and that the RT model of hot H atom production is required. Arguments for the sheath-collision interpretation that are contrary to Mills' claims 3,5,8 include: ͑a͒ The maximum observed 19,20,23 Doppler shifts are consistent with the discharge voltage; ͑b͒ both redshifts and blueshifts are predicted from gas and surface scattering of fast H atoms, with the asymmetry depending on the direction of observation relative to the electric field; [22][23][24] ͑c͒ excess H ␣ broadening is observed 16,23 for non-RT mixtures of Ne-H 2 and Kr-H 2 ; and ͑d͒ the observed excess broadening for excited H atoms leaving the cathode can be dominant or very small, depending on the cathode material.…”

“…20,22 Reference 1 cites Mills et al 3 as evidence that the sheath-collision model fails and that the RT model of hot H atom production is required. Arguments for the sheath-collision interpretation that are contrary to Mills' claims 3,5,8 include: ͑a͒ The maximum observed 19,20,23 Doppler shifts are consistent with the discharge voltage; ͑b͒ both redshifts and blueshifts are predicted from gas and surface scattering of fast H atoms, with the asymmetry depending on the direction of observation relative to the electric field; [22][23][24] ͑c͒ excess H ␣ broadening is observed 16,23 for non-RT mixtures of Ne-H 2 and Kr-H 2 ; and ͑d͒ the observed excess broadening for excited H atoms leaving the cathode can be dominant or very small, depending on the cathode material. 19,20,22 The linearity with the current of the fast excited H atom emission from pure H 2 and H 2 -Ar mixtures in dc drift tubes 19,25 for ϳ10 −7 A/cm 2 and in glow discharges 20 for ϳ10 −2 A/cm 2 is strong evidence against the production of the fast H atoms by Mills' RT process, 2 with its quadratic dependence on electron current.…”