Ignition phase of a pulsed microwave-excited oxygen plasma

Brockhaus, A.; Behle, St.; Georg, Andreas; Engemann, J.

doi:10.1051/jp4:1998725

Cited by 3 publications

(2 citation statements)

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“…Approximately 4 µs later a much brighter emission of Ar * and Ar + is visible on one side of the discharge chamber. We observed that the ignition point is always located at that side of the discharge chamber where the movable plunger of the SLAN matching network is mounted, independent of gas type or pressure [33]. After the ignition an azimuthal and radial extension of Ar * can be seen.…”

Section: Ignition Phase the First Detectable Emission Ofmentioning

confidence: 78%

Time-resolved investigations of pulsed microwave excited plasmas

Behle

Brockhaus

Engemann

2000

Plasma Sources Sci. Technol.

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Pulsed microwave excited (2.45 GHz) argon plasmas generated by a slot antenna type plasma source are investigated by various diagnostic tools. Through the combined use of time-resolved planar optical emission spectroscopy (TPOES), microwave interferometry (MWI) and Langmuir probes the temporal behaviour of the electron density, n e (t), and effective electron temperature, T e (t), for the pulse frequency range of 0.2-20 kHz are measured. Additionally, from TPOES maps of Ar * and Ar + , the qualitative spatially and time-resolved electron temperature distribution is derived. The n e (t) and T e (t) rise and decay times are almost constant throughout the examined frequency range. A n e (t) rise time of 1 ms and a decay time of 0.6 ms is derived from probe and MWI data at 5 Pa. A T e (t) rise time between 5 and 10 µs and a decay time between 50 µs and 80 µs is derived from TPOES and probe measurements at 5 Pa. The maximum time-averaged electron density, ne , at 5 Pa is obtained at a pulse frequency f of 200 Hz. With increasing pressure and power the pulse frequency f at which a maximum of ne is reached decreases to f ≈ 50 Hz. The temporal n e (t) and T e (t) behaviour for the investigated pressure range is described by a simple set of equations based on the 'Global Model' of pulsed plasmas. It can be concluded that the electron loss rate ν loss controls both the rise and decay times of n e (t). The ν loss is in the first order a function of the plasma system dimensions and geometry. The decay of T e (t) depends on ν loss and the losses due to inelastic scattering.

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Section: Ignition Phase the First Detectable Emission Ofmentioning

confidence: 78%

Time-resolved investigations of pulsed microwave excited plasmas

Behle

Brockhaus

Engemann

2000

Plasma Sources Sci. Technol.

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“…The authors described how the high electric field at breakdown leads to an enhancement of the ionisation frequency, and therefore to an increase of the electron density compared to continuous mode operation [28]. Spatial analysis of the plasma ignition in a circular radiative slotted waveguide reactor showed that, even when the electron density is nearly uniform at the steady state, the discharge ignites in very specific places [29]. In contrast to the many studies of pulsed RF plasmas, systematic time resolved investigations of pulse-modulated microwave discharges, in particular concerning properties of the electron component, are relatively uncommon.…”

Section: Introductionmentioning

confidence: 99%

Langmuir probe diagnostic studies of pulsed hydrogen plasmas in planar microwave reactors

Rousseau

Teboul²,

Lang

et al. 2002

Journal of Applied Physics

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Langmuir probe techniques have been used to study time and spatially resolved electron densities and electron temperatures in pulse-modulated hydrogen discharges in two different planar microwave reactors (f microwave = 2.45 GHz, t pulse = 1 ms). The reactors are (i) a standingwave radiative slotted waveguide reactor and (ii) a modified travelling-wave radiative slotted waveguide reactor, which generate relatively large plasmas over areas from about 350 cm 2 to 500 cm 2 . The plasma properties of these reactor types are of particular interest as they have been used for basic research and for plasma processing, e.g. for surface treatment and layer deposition. In the present study the pressures and microwave powers in the reactors were varied between 33 and 55 Pa and 600 and 3600 W, respectively. In regions with high electromagnetic fields shielded Langmuir probes were used to avoid disturbances of the probe characteristic. Close to the microwave windows of the reactors both the electron density and the electron temperature showed strong inhomogeneities. In the standing-wave reactor the inhomogeneity was found to be spatially modulated by the position of the slots. The maximum value of the electron temperature was about 10 eV and the electron density varied between 0.2 and 14×10 11 cm -3 . The steady state electron temperature in a discharge pulse was reached within a few tens of microseconds whereas the electron density needed some hundreds of microseconds to reach a steady state. Depending on the reactor the electron density reached a maximum between 80 and 200 µs after the beginning of the pulse.2

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