Direct measurement of ion and electron flux ratio at their respective sheath-edges and absence of the electron Bohm criterion effects

Jin, Chenyao; Yip, Chi-Shung; Zhang, Wei; Jiang, Di; Xu, G. S.

doi:10.1088/1361-6595/ac9b8d

Cited by 5 publications

(5 citation statements)

References 60 publications

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“…They analyzed each I-V trace and obtained variation of the saturation current with the changes of A L /A S . They concluded that (A L /A S ) crit,Ar is ∼180 for argon plasma, as shown in figure 4, which is consistent with the conventional theory prediction that ions enter the ion sheath with the ion Bohm criterion and electrons enter the electron sheath randomly at electron thermal velocity, given that (A L /A S ) crit = (m i /(2.3m e )) 1/2 [23].…”

Section: Experimental Studies On the Area Limitation Of The Langmuir ...supporting

confidence: 77%

“…Yip et al discovered that even when the ratio of the area of the Langmuir probe area to the chamber wall area A L /A S is less than or near (m i /(2.3m e )) 1/2 as predicted by conventional theory, a small virtual cathode can still form near the probe, affecting the I-V curve and leading to a significant error of ∼30% in electron temperature measurement [35]. Jin et al later conducted experiments in Diagnostics Test Source II (DTS-II) [23,36], as shown in figure 3(a), in argon plasma and scanned A L /A S of an ADLP ranging from 15-365 with the 2 mm diameter small probe A S unchanged and the diameter of large probe A L varying from 8-40 mm. The plasma parameters were measured by a single Langmuir probe biased with respect to the grounded chamber wall and the ADLP is floating and its two probe tips were biased with respect to each other, as shown in figures 3(b) and (c).…”

Section: Experimental Studies On the Area Limitation Of The Langmuir ...mentioning

confidence: 98%

“…Recently, a series of theoretical studies proposed an electron presheath and electron Bohm criterion so that electrons do not enter an electron sheath with a random thermal flux, but instead with a fluid velocity known as the electron Bohm speed [21,22]. Experimental studies aimed at testing the effects of this electron Bohm criterion instead revealed other mechanisms that affect the design limitation of the Langmuir probe area [23]. These will be discussed in detail in the following sections.…”

Section: Principle Of the Langmuir Probementioning

confidence: 99%

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Presheath formation and area design limit satellite-based Langmuir probes

Jin

Yip

Sun

et al. 2023

Plasma Sci. Technol.

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In this article, the effect of finite conductive surface area of a satellite on the use of satellite-based Langmuir probes is reviewed in light of the basic theory of asymmetric double Langmuir probes (ADLPs). Recent theoretical and experimental works have discussed electron sheath/presheath formation and the electron Bohm criterion along with their implications on the satellite-based Langmuir probes. The effects predicted by the latest theory of electron Bohm criterion were not experimentally observed and the experimental result remains supportive of a critical area ratio (AL/AS)crit = (mi/(2.3me))1/2 between the probe area AS and the satellite area AL as conventionally believed. A satellite-based Langmuir probe must satisfy this criterion to physically act as a single Langmuir probe. However, experimental investigations also found that high-energy electrons adversely affect (AL/AS)crit and a Langmuir probe’s signal quality by giving additional electron current to AL. With these results, a series of limitations of maximum probe area are derived when designing satellite-based Langmuir probes, with consideration of both mission what the satellite aims and plasma where the satellite-based probe works. This series of proposed measures is expected to only partially alleviate the effect of the inadequate satellite surface area on the application of satellite-based Langmuir probes. Using a larger satellite to carry a Langmuir probe remains the most viable means to obtain precise space plasma parameters.

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Section: Experimental Studies On the Area Limitation Of The Langmuir ...supporting

confidence: 77%

Section: Experimental Studies On the Area Limitation Of The Langmuir ...mentioning

confidence: 98%

Section: Principle Of the Langmuir Probementioning

confidence: 99%

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Presheath formation and area design limit satellite-based Langmuir probes

Jin

Yip

Sun

et al. 2023

Plasma Sci. Technol.

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“…Figure 3 shows the resultant effective electron temperature T eff obtained by analyzing simulated I-V traces of the ADLP and the EDLP with a typical bi-temperature Maxwellian EEDF analysis method [14,23,[33][34][35][36][37], benchmarked with the real T eff adapted in these computations. It can be shown that even when I L,is > I S,es , i.e.…”

Section: Adlp and Edlpmentioning

confidence: 99%

“…As micro-satellites become increasingly popular in space-probing missions, the area of single Langmuir probes to be installed in these satellites is expected to be limited with increasing severity. The use of symmetric DLPs instead of single Langmuir probes has been adapted in some satellite designs to mitigate this problem [12,13], but the signal quality of DLPs is limited by their ion saturation current [14], and they often have issues resolving an accurate EEDF in the presence of energetic electrons [23].…”

Section: Introductionmentioning

confidence: 99%

A self-balanced electron-emissive double Langmuir probe drawing no electron loss from its diagnosed plasma

Yip,

Jin,

Zhang

et al. 2023

Plasma Sources Sci. Technol.

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In this work, a new form of double Langmuir probe system, an Emissive Double Langmuir probe (EDLP), which connects a collecting probe tip and an electron emitting probe tip to form a double Langmuir probe system, has been proposed as a replacement of the currently more common asymmetric double Langmuir probes (ADLP). The EDLP was both computationally and experimentally investigated in this work. Using an emissive probe to provide an emission current IE to balance the electron collection current IC,e, the EDLP can obtain a full I-V trace when IE,TL > IC,es and be used in a similar manner with a single Langmuir probe except the EDLP, as with the ADLP, does not measure the local plasma potential. IE,TL >> IC,es can be realized on an EDLP without needing the much larger ion collection area required by the ADLP, and at IE,TL ~ 2IC,es the relative error between the EDLP and a single Langmuir probe is ~15% due to SCL effects, which is better than that of the ADLP at ~30% under similar conditions. The performance of an EDLP depends on whether its electron emission current sufficiently offsets its electron collecting current, making it particularly fitted for scenarios where plasma density is low but a large probe is difficult to employ due to limited balancing ion current. This makes the EDLP potentially useful on satellites which operates in very low temperature plasmas with a limited ion loss area to balance a Langmuir probe’s electron collecting current. With the advances of highly emitting materials, EDLPs are expected to significantly remove design barriers of Langmuir probes on satellites.

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Effects of high energy electrons on electron temperature measurements of asymmetric double Langmuir probes

et al. 2023

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In this work, electron temperature was measured with both the asymmetric double Langmuir probe (ADLP) and the single Langmuir probe to investigate the reliability of the ADLP on the electron temperature measurement in multi-temperature Maxwellian plasmas. A series of I–V traces of the ADLP were obtained at various plasma conditions with different area ratios and analyzed with different methods including conventional ADLP analysis and two-temperature Maxwellian fitting with results measured by a single planar Langmuir probe analyzed with three-temperature Maxwellian fitting as reference. The measured Te of the ADLP is found to reflect that of the temperature of the degraded primary electrons when the area ratio of the probe tips is close to ∼16 and approaches the real effective electron temperature as the area ratio increases to a value of ∼30% higher than that measured by a single Langmuir probe, which occurs even when the area ratio is higher than the flux ratio of electrons and ions entering their respective sheaths. This effect is consistent with the distortion effect of Langmuir probe I–V traces caused by the presence of hotter electron species, which was computationally reconstructed and agreed well with the experimental observations. This result implies that an area ratio, possibly ∼20 times much larger than what was conventionally assumed, is needed for an ADLP to be reliably treated as a single Langmuir probe in practical settings, where electron energy distribution functions of plasmas are generally expected to be multi-temperature Maxwellian. This effect is also analogous to the current balance between a single Langmuir probe and the device wall, implying that this effect would also affect the application of the single Langmuir probe in plasmas, where the ion loss to the device wall can be reduced, such as plasmas in miniaturized devices, strong magnetic fields, or a highly ion-neutral collisional environment.

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Direct measurement of ion and electron flux ratio at their respective sheath-edges and absence of the electron Bohm criterion effects

Cited by 5 publications

References 60 publications

Presheath formation and area design limit satellite-based Langmuir probes

Presheath formation and area design limit satellite-based Langmuir probes

A self-balanced electron-emissive double Langmuir probe drawing no electron loss from its diagnosed plasma

Effects of high energy electrons on electron temperature measurements of asymmetric double Langmuir probes

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