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| {{Unreferenced|date=December 2009}}
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| Plasma that are excited by propagation of electromagnetic surface waves are called '''surface-wave-sustained'''. [[Surface wave]] plasma sources can be divided into two groups depending upon whether the plasma generates part of its own [[waveguide]] by [[ionisation]] or not. The former is called a [[self-guided plasma]]. The surface wave mode allows to generate uniform high-frequency-excited plasmas in volumes whose lateral dimensions extends over several wavelengths of the electromagnetic wave, e.g. for microwaves of 2.45 GHz in [[vacuum]] the [[wavelength]] amounts to 12.2 cm.
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| For a long time, [[microwave plasma|microwave]] [[plasma source]]s without magnetic field have not been considered suitable for the generation of high density plasmas. [[Electromagnetic wave]]s cannot propagate in [[over-dense plasma]]s. The wave is reflected at the plasma surface due to the [[skin effect]] and becomes an [[evanescent wave]]. Its penetration depth corresponds to the
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| [[skin depth]] <math>\delta</math>,
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| which can be approximated by
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| :<math>\delta \simeq | |
| c\,\big/\sqrt{\omega_{p_e}^2 - \omega^2}. </math>
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| The non-vanishing penetration depth of an evanescent wave opens an alternative way of heating a plasma: Instead of ''traversing'' the
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| plasma, the conductivity of the plasma enables the wave to propagate ''along'' the plasma surface. The wave energy is then transferred to the plasma by an [[evanescent wave]] which enters the plasma perpendicular to its surface and [[exponential decay|decays exponentially]] with the [[skin depth]]. 'Transfer mechanism allows to generate [[over-dense plasma]]s with electron densities beyond the critical density.
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| Surface-wave-sustained plasmas (SWP) can be operated in a large variety of recipient geometries. The pressure range accessible for surface-wave-excited plasmas depends on the process gas and the diameter of the recipient. The larger the chamber diameter, the lower the minimal pressure necessary for the SWP mode. Analogously, the maximal pressure where a stable SWP can be operated decreases with increasing diameter. The [[numerical modelling]] of SWPs is quite involved. The plasma is created by the [[electromagnetic wave]], but it also reflects and guides this same wave. Therefore, a truly [[self-consistent]] description is necessary.
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| {{DEFAULTSORT:Surface-Wave-Sustained Mode}}
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| [[Category:Waves in plasmas]]
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Revision as of 16:50, 8 February 2014
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