Mode Structure of a Transparent Cathode Discharge

Hardiment, Tom; Bowden, M. D.

doi:10.1109/tps.2019.2919908

Cited by 5 publications

(5 citation statements)

References 20 publications

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“…In helium the axial and radial spatial elements are associated with distinct colours, with the hollow cathode and axial glow a bright green and the radial emission pale orange. Photographs showing spatial distributions of emission for some transitional states over this range can be found in our previous studies [1,2]. The colour variation results from emission at different principal wavelengths, that correspond with large respective cross sections for excitation by electrons and ions, indicating different sets of collisional processes in the two modes caused by electrons and heavy particles.…”

Section: Results and Analysismentioning

confidence: 66%

“…In figure 9(iv), the anode has dropped and turned relative to the cathode, which can be seen to cause a splitting effect for beams on the right of the image. In previous descriptions of these discharges [1,2] we noted characteristic emission occurring along the axial line between open cathode end and cham- ber wall, that in helium evolves from a bright green plume to a fainter narrow beam over pressures p = 15-5 Pa. This axial beam emission is quite faint for conditions illustrated in figure 9, and not particularly evident in the photographs.…”

Section: Beam Mode Emission Distributionmentioning

confidence: 62%

“…Before concentrating upon optical emission from the beam mode, we first summarise some general procedures and operating characteristics described in previous work [1,2].…”

Section: Results and Analysismentioning

confidence: 99%

“…We refer to the 'beam' mode because of a beam-like distribution of emission, that has been observed to remain similar in appearance over ranges of conditions in various gas species [1,2]. This is illustrated with photographs of beam mode discharges in our standard electrode arrangement in figure 9 (see also figures 1 and 2(i)).…”

Section: Beam Mode Emission Distributionmentioning

confidence: 95%

“…inertial electrostatic confinement (IEC) device with a coaxial arrangement of cylindrical wire-grid electrodes, in which a central cathode is biased to a high DC voltage. We have previously described [1,2] how the beam mode operates at pressures too low for a hollow cathode mode to sustain, and also how the principal colour of optical emission from the beam mode in helium indicates collisional processes that are caused significantly by energetic ions and neutrals. In this paper we shall further examine this unusual emission spectrum, and investigate how the beam-like form of the discharge relies upon physical properties of the experimental set-up.…”

Section: Introductionmentioning

confidence: 99%

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Optical emission from a ‘beam mode’ transparent cathode glow discharge

Hardiment

Bowden

2021

Plasma Sources Sci. Technol.

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We investigate optical emission from a low-pressure ‘beam mode’ inertial electrostatic confinement glow discharge, created using cylindrical grid electrodes, having cathode inside a grounded, concentric anode. Spectral line distributions were measured in helium from this and a hollow cathode mode, with four lines emitted from singlet and triplet states with n = 3 and L = P and D compared against simple models for impact excitation by electrons and by ions and neutrals, suggesting much beam mode emission is caused by fast neutrals, and a significant component also caused by electrons. Beam mode emission occurs in a pattern of radial lines, that pass through aligned electrode apertures and extend across the chamber. Shadows cast by the electrode wires indicate electrically-neutral, beam-like sources of excitation, that cross the electrode assembly from bright radial lines in the opposing inter-electrode space, and calculated potential distributions show lensing surfaces around the anode grid apertures, focussing for inward-drifting ions. These indicate the emission pattern is caused by radially-convergent ion beams, and co-linear beams of fast neutrals produced in these. Emission was also observed with various alterations made to the electrode arrangement: with the anode removed, no beams were observed; with the cathode apertures rotated out of phase with those of the anode, bright radial beams between the electrodes followed the distribution of anode apertures; similar beams appeared with the grid cathode replaced by a solid version. In these experiments, progressive obstruction of pathways through the cathode caused increasing reduction in the beam pattern of emission beyond the anode radius, and in discharge perveance at similar pressure and voltage. Beam-like emission was also observed for a parallel-planar configuration, in which a cathode grid was held between two identical anode grids. The beam mode is shown to be a convergent, anode-focussed ion beam discharge, distinct to the star mode described elsewhere.

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Section: Results and Analysismentioning

confidence: 66%

Section: Beam Mode Emission Distributionmentioning

confidence: 62%

“…Before concentrating upon optical emission from the beam mode, we first summarise some general procedures and operating characteristics described in previous work [1,2].…”

Section: Results and Analysismentioning

confidence: 99%

Section: Beam Mode Emission Distributionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Optical emission from a ‘beam mode’ transparent cathode glow discharge

Hardiment

Bowden

2021

Plasma Sources Sci. Technol.

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Influence of cathode grid geometry upon mode structure of a transparent cathode discharge

Hardiment

Bowden

2020

Physics of Plasmas

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We measured current–voltage and optical emission for self-sustained discharges obtained using two forms of cylindrical wire grid cathodes, having either an enclosed or an open end. Enclosure of the open end extended the low-pressure range for a “cathode-confined” or CC mode, from around 12.5 Pa to below 3.5 Pa, conditions at which a “beam” mode discharge otherwise occurs. The modification also caused a dark space to envelop the glow within the cathode, bridged by a bright emission resembling plume for the CC mode, and an electron beam for the beam mode. We explain these results by treating the CC mode as a hollow cathode discharge, for which only γ-electrons that suffer inelastic loss before escaping the cathode grid are significant. For the two cathodes, respective degrees of electron confinement possible for the different sheath configurations predict the low-pressure ranges, and the calculated values of cathode fall for self-sustenance by the hollow cathode effect agree approximately with the experimental voltages across a range of pressures. Plume- and beam-like forms of emission indicate inherently different electron energies, consistent with bulk transport across potential distributions characteristic to the mode. Where these features bridge the enclosed cathode boundary, this shows existence of an otherwise closed potential surface within the cathode, confirmed by the geometry of the plume-CC mode configuration, where the relationship between the main glow and plume interface surfaces indicates the arrangement to self-organize in a state of non-ambipolar current flow. Similarities in the mode structure reported elsewhere for related discharges indicates the findings to be relevant for these also.

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Paschen curves and current–voltage characteristics of large-area short glow discharge with different electrode structures

et al. 2020

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In this work, the Paschen curves and current–voltage characteristics of three large-area short glow discharge structures with grid and solid plate electrodes are studied. The study of the Paschen's curves reveals that Paschen's law is broken for all three investigated electrode structures. It is shown that the experimentally measured Paschen curves are well approximated with a modified Paschen's law. A comparison of the current–voltage characteristics of the short glow discharge in the three types of electrode structures reveals that the use of grid electrodes allows for the increase in the discharge current. The effects of the electrode gap, which were varied from 1 mm to 7 mm, on the Paschen curves and current–voltage characteristics of short glow discharges are also investigated.

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Mode Structure of a Transparent Cathode Discharge

Cited by 5 publications

References 20 publications

Optical emission from a ‘beam mode’ transparent cathode glow discharge

Optical emission from a ‘beam mode’ transparent cathode glow discharge

Influence of cathode grid geometry upon mode structure of a transparent cathode discharge

Paschen curves and current–voltage characteristics of large-area short glow discharge with different electrode structures

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