An emissive probe with a rhenium filament for measuring plasma potential in a radio frequency oxygen plasma

Wilson, Ellis; Jeong, Jongtae; Hershkowitz, N.

doi:10.1063/1.1469674

Cited by 9 publications

(7 citation statements)

References 17 publications

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“…Tungsten is an unsuitable choice for an emissive probe if oxygen is present in the plasma [62]. A heated tungsten wire will rapidly oxidize in an oxygen-rich environment and tungsten oxide is many orders of magnitude less conductive than pure tungsten.…”

Section: Methodsmentioning

confidence: 99%

Emissive probes

Sheehan¹,

Hershkowitz²

2011

Plasma Sources Sci. Technol.

199

211

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For over 80 years emissive probes have been used to measure plasma potential and a wide variety of methods for interpreting probe data now exists. Constructions, heating methods and measurement techniques are reviewed in detail and their various strengths and limitations are compared. Additionally, several novel uses for emissive probes, such as measuring electron temperature are presented. This review also includes tables of recommendations for emissive probe design given the type of plasma and desired measurements.

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Section: Methodsmentioning

confidence: 99%

Emissive probes

Sheehan¹,

Hershkowitz²

2011

Plasma Sources Sci. Technol.

199

211

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“…Emissive probes are used for direct measurements of the plasma potential and its fluctuations in various types of plasmas -e. g. [1,2,3]. These quantities cannot be directly obtained by "cold" (i. e. non-emissive) Langmuir probes.…”

Section: Introductionmentioning

confidence: 96%

Experimental investigation of the change of the electron saturation current of a dc-heated emissive probe

et al. 2006

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We report on experimental investigations of the change of the electron saturation current of a dc-heated emissive probe with the probe heating current. According to the simple theory of the emissive probe, the electron saturation current should not be affected by emission. However, in many experiments a variation of the electron saturation current with the emission current was observed. We consider two possible reasons for such variations: (a) the influence of the space charge around the probe shaft, (b) the change of the work function of the probe surface material due to heating. We tried to find sufficient experimental evidence for supporting one or the other (or both) of these two explanations. We used two different types of plasma to validate the results: a cylindrical magnetron plasma and the non-magnetized plasma of a DP machine. From our experiments follows that the electron saturation current of the emissive probe is affected by the space charge effect as well as it depends on the probe wire material. : 52.25.Xz, 52.70.Ds PACS

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“…Another important, however, indirect method was later described by Smith et al [39] who argued that the inflection point of an emissive probe characteristic, at moderate emission current, yields a more precise measure for the plasma potential. Later on, eminent contributions to the plasma diagnosis with emissive probes were made especially by Hershkowitz and his group [40][41][42][43][44][45][46][47][48][49][50]. Other papers were devoted mainly to the experimental and theoretical principles of emissive probes [19,21,[33][34][35][36].…”

Section: Electron Emissive Probes (Eep) 21 Basics Of Electron Emissive Probes (Eep)mentioning

confidence: 99%

Plasma potential probes for hot plasmas

et al. 2019

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Plasma probes are well established diagnostic tools. They are not complicated, relatively easy to construct and to handle. The easiest and fastest accessible parameter is their floating potential. However, the floating potential of a cold probe is not very significant. Much more important and relevant is the plasma potential. But in most types of plasmas, consisting mainly of electrons and only positive ions, the floating potential is more negative than the plasma potential by a factor proportional to the electron temperature. Obviously this is due to the much higher mobility of the electrons. We present a review on probes whose floating potential is close to or ideally equal to the plasma potential. Such probes we name Plasma Potential Probes (PPP) and they can either be Electron Emissive Probes (EEP) or so-called Electron Screening Probes (EPS). These probes make it possible to measure the plasma potential directly and thus with high temporal resolution. An EEP compensates the plasma electron current by an electron emission current from the probe into the plasma, thereby rendering the current-voltage characteristic symmetric with respect to the plasma potential and shifting the floating potential towards the plasma potential. Only the simplest case of an EEP floating exactly on the plasma potential is discussed here in which case no sheath is present around the probe. An ESP, principally operable only in strong magnetic fields, screens off most of the plasma electron current from the probe collector, taking advantage of the fact that the gyro radius of electrons is usually much smaller than that of the ions. Also in this case we obtain a symmetric current-voltage characteristic and a shift of the probe's floating potential towards the plasma potential. We have developed strong and robust EEPs and two types of ESPs, called BUnker Probes (BUP), for the use in the Scrape-Off Layer (SOL) of Medium-Size Tokamaks (MST), and other types of strongly magnetized hot plasmas. These probes are presented in detail.

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An emissive probe with a rhenium filament for measuring plasma potential in a radio frequency oxygen plasma

Cited by 9 publications

References 17 publications

Emissive probes

Emissive probes

Experimental investigation of the change of the electron saturation current of a dc-heated emissive probe

Plasma potential probes for hot plasmas

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