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IEE Proceedings - Science, Measurement and Technology

Volume 141, Issue 2, March 1994

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Volume 141, Issue 2

March 1994

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Editorial: Diagnosis and measurement of electrrical discharges

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    • Laser-induced plasmas and resonance ionisation spectroscopies
      Diagnostics of DC-pulse SiH4 plasmas using laser-induced fluorescence and optical emission spectroscopy
      • Author(s): T. Nakano ; T. Hokaya ; Y. Murooka ; Y. Ichikawa ; H. Sakai
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 89 –93
      • DOI:  10.1049/ip-smt:19949980
      • Type: Article
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      • p. 89 –93 (5)
        Plasmas produced with short-pulse power show promise for deposition of hydrogenated amorphous silicon films (a-Si:H). For high electron temperature and density compared to those in continuously excited plasmas, the reactants for a-Si:H deposition can be produced efficiently in the pulse plasmas. In the afterglows, the average energy of ions impinging on the substrate is expected to be low, allowing one to grow less-damaged films through reactions of long-lifetime reactants such as SiH3. To optimise the pulse plasmas for the a-Si:H deposition process, it is necessary to understand the production and transport of the reactants in connection with the plasma structure. DC-pulse plasmas through pure SiH4 and SiH4/H2 mixtures are diagnosed by laser-induced fluorescence. The spatial profiles of SiH radicals are measured to investigate the plasma structure. Optical emission spectroscopy and the time-resolved Langmuir probe measurement are also conducted to characterise the plasma in terms of electron density and temperature. In a DC-pulse plasma through hydrogen, the electron density reaches approximately 1011 cm-3 one to two orders of magnitude higher than the electron densities in conventional radio-frequence (RF) plasmas. For a SiH4/CF4 mixture, CF4 molecules are dissociated in the DC-pulse plasmas for the high energy electrons produced in the initial stage of plasma production. By contrast, they are scarcely decomposed in continuous RF plasmas. The spatial profiles of SiH density for the DC-pulse plasmas in pure SiH4 suggest that the discharge has no positive column and that SiH radicals are produced mostly in the negative glow.
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      Spectroscopic and image intensified investigations of RF plasmas in H2 and CH4 mixtures
      • Author(s): H. Itoh ; Y. Takeyama ; M. Ikeda ; K. Satoh ; Y. Nakao ; H. Tagashira
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 95 –98
      • DOI:  10.1049/ip-smt:19949923
      • Type: Article
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      • p. 95 –98 (4)
        A computer-aided spectroscopic investigation system by means of an image processing technique has been developed for diagnosing various processing plasmas. This system, which is composed of a monochromator, two image intensifiers, a CCD camera and a personal computer, is characterised by the introduction of a digital signal processor and spatial filtering treatment of image data for fast image operations. The spectroscopic system is used to diagnose RF plasmas in H2 and CH4 mixtures and in pure H2. The results show that this system enables a spatiotemporally resolved optical emission spectra from plasmas to be obtained. It is found that the spatial and temporal resolutions are, respectively, 50 µm and 800 ns throughout the experiment, and that the needed operating time for detection of one spatial profile of the selected spectrum is 70 s.
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      Chromatic monitoring for the processing of materials with plasmas
      • Author(s): P.C. Russell ; I. Khandaker ; E. Glavas ; D. Alston ; .V. Smith ; G.R. Jones
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 99 –104
      • DOI:  10.1049/ip-smt:19949850
      • Type: Article
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      • p. 99 –104 (6)
        A non-invasive monitoring system for material-processing plasmas has been developed based on chromatic modulation. The monitor consists of two parts, one for monitoring the emission spectra of plasmas and the second for monitoring the thickness of films on semiconductors during etching or deposition. These chromatic systems offer significant speed advantages over equivalent spectroscopic techniques. Both systems have been tested on a variety of plasma chambers and typical results from both systems are presented. Chromatic monitoring provides rapid feedback on the state of a plasma and on film thickness, providing the possibility for real-time monitoring and control of the plasma state. Further enhancement of the chromatic technique allows two dimensional monitoring of the plasma, providing information on its uniformity.
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      Use of an ion energy analyser-mass spectrometer to measure ion kinetic-energy distributions from RF discharges in argon-helium gas mixtures
      • Author(s): J.K. Olthoff ; R.J. Van Brunt ; S.B. Radovanov ; J.A. Rees
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 105 –110
      • DOI:  10.1049/ip-smt:19949920
      • Type: Article
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      • p. 105 –110 (6)
        A mass spectrometer equipped with an electrostatic ion energy analyser has been used to measure the kinetic-energy distributions of ions sampled through an orifice in the grounded electrode of a parallel-plate radio-frequency (RF) discharge cell. Kinetic-energy distributions are presented for Ar+, Ar2+, Ar++, He+, and ArHe+ sampled from argon-helium plasmas with helium concentrations ranging from 0-95 mole percent, applied peak-to-peak RF voltages of 200 V, and gas pressures of 13.3 Pa. Variations in the ion kinetic-energy distributions and ion fluxes observed for different gas mixtures demonstrate the ability of this diagnostic technique to monitor plasma conditions and to investigate the ion kinetic processes occurring in the system.
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      Linear-geometry electric-field probe for DC corona measurements
      Characterising the discharge development due to surface contamination in GIS using the UHF technique
      Spectroscopic observation of high breaking capacity fuse arcs
      • Author(s): L.A.V. Cheim  and  A.F. Howe
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 123 –128
      • DOI:  10.1049/ip-smt:19949922
      • Type: Article
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      • p. 123 –128 (6)
        The complex nature of arcing phenomena In high breaking capacity fuses has made arc modelling and simulation extremely difficult. This paper describes an experimental spectroscopic technique to continuously investigate arc parameters, such as temperature, in this type of fuse. Arc probing was achieved by the use of an optical fibre and the spectroscopy consisted of the continuous acquisition of plasma emissions of radiation by an opto-electronic system. Using quantum-mechanics expressions for the computation of the results, the arc temperature was estimated to be about 20 000 K, which agrees with previous research. There was little variation of temperature with time. This information is of great value for those developing dynamic representations of fuse arcs.
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      Low-power optical current measurement system employing a hybrid transmitter
      • Author(s): N.A. Pilling ; R. Holmes ; G.R. Jones
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 129 –134
      • DOI:  10.1049/ip-smt:19949754
      • Type: Article
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      • p. 129 –134 (6)
        A high-performance current measurement system has been developed for use in power systems. Active electronic components are sited in a transmitter on the power line, with power for these components being derived from the line via a current transformer(CT). Measurement information is transmitted to the remote receiver by an optical fibre, which provides electrical isolation from the line and immunity to the electromagnetic interference commonly present in such installations. The optical fibre also allows the transmitter to be sited up to kilometres from the receiver. A current transformer is used to derive measurement signal proportional to the line current. The active circuit, in conjunction with a pulsed frequency modulation optical transmission system, achieves new standards of performance for low power consumption. Thus the transmitter will operate from line currents of less than 1 A. The CTs used in the transmitter are subject to different design criteria from those used in conventional CTs, and particular attention is paid to optimised designs for both types of CT.
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      Simple heat flux density probe for industrial plasmas
      Diagnostic techniques for atmospheric streamer discharges
      • Author(s): Y.L.M. Creyghton ; E.M. van Veldhuizen ; W.R. Rutgers
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 141 –147
      • DOI:  10.1049/ip-smt:19941017
      • Type: Article
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      • p. 141 –147 (7)
        Fast electrical and optical diagnostics are required for the analysis of atmospheric streamer discharges. This is illustrated for the case of positive streamer corona produced along wire electrodes by high voltage pulses with rise times of tens of nanoseconds. Electrical measurements with a high time resolution reveal the energy input in two discharge phases (primary and secondary streamer). The discharge structure is visualised using a gated image intensifier. The number of streamers per unit length of anode wire and the streamer diameter are determined. The streamer velocity is measured with a time-of-flight method using two optical fibres. Time-resolved spectroscopic measurements of the intensity ratio of N2+ and N2 emission lines reveal that the average electron energy in the primary streamer phase is significantly higher than in the subsequent secondary streamer. The neutral gas temperature in the discharge is determined from the rotational structure of an N2 emission line and is only slightly above the background gas temperature. Schlieren photographs visualise the heat dissipated in residual streamer channels.
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      Metal vapour densities in a pseudospark switch
      • Author(s): G. Lins  and  W. Hartmann
      • Source: IEE Proceedings - Science, Measurement and Technology, Volume 141, Issue 2, p. 148 –152
      • DOI:  10.1049/ip-smt:19949921
      • Type: Article
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      • p. 148 –152 (5)
        A pseudospark switch with a cathode made of a composite material containing 95% of tungsten and small amounts of iron, copper, and nickel was subjected to current pulses of 12 kA in amplitude and 1.6 µs duration. Laser-induced fluorescence was used to measure the contribution of each metal to the number density of neutral vapour released by the pseudospark discharge. The vapour composition differed considerably from the composition of the cathode material. In particular, the maximum copper vapour density amounted to 1.5 *1018 m-3 while the maximum tungsten density was as low as 2 *1017 m-3. It is concluded that the loss of copper from the electrode material may result in disintegration of the electrode material after sufficient number of discharges. Hence low-melting additions to the cathodes of pseudospark switches should be avoided. A comparison of the ratios of the vapour densities of the constituents of the cathode material with the corresponding ratios of the equilibrium vapour pressures revealed that there are regions of extremely high (T>5000 K) and comparatively low (T approximately=1500 K) temperature on the cathode. This adds evidence to the view that the electron emission at the cathode of pseudosparks occurs from individual microscopic emission sites rather than from a surface heated homogeneously to a uniform temperature.
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