Electron-induced secondary electron emission coefficient of lithium, tungsten and stainless steel surfaces exposed to low-pressure plasmas

Oyarzábal, E.; Martín-Rojo, A.B.; Tabarés, F.L.

doi:10.1016/j.jnucmat.2014.04.046

Cited by 23 publications

(12 citation statements)

References 23 publications

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“…These materials exhibit large wall velocities that are close to each other. This is consistent with the experimental data 7,25 . These materials have comparable SEE yields and first crossover energies (Table I).…”

Section: A Multipolar Experimentssupporting

confidence: 93%

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Plasma sheath material induced dependence due to secondary electron emission

et al. 2020

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Plasma sheaths in front of six different materials samples (BN, BNSiO 2 , Al 2 O 3 , SiO 2 , stainless steel and silicon) used in various experiments and devices (Hall thrusters, plasma discharge, microelectronics) are studied using the Laser Induced Fluorescence diagnostic. The specific Secondary Electron Emission (SEE) yield of each material is expected to induce differences in the sheath structure from one sample to another. The experiments are carried out in two different plasma discharges (multipolar device and ECR device), exhibiting distinct electron distribution functions: bi-maxwellian and maxwellian. The agreement between the two experiments is good and allow to classify the materials in a consistent way regarding their SEE yields. The multipolar experiments results are compared to a 1D kinetic sheath model and a 1D-1V kinetic sheath simulation code. The predictions of the model are discussed and are in good agreement with previous theory. The influence of the low energy impinging electrons on the SEE yield and emissive sheaths is investigated with the code.

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Section: A Multipolar Experimentssupporting

confidence: 93%

“…The last sample is a 1 cm squared piece of silicon (Si). The samples were chosen for their various SEE yields, 7 ; the steel's yield was experimentally obtained in plasma conditions 25 ; the SiO 2 and Si yields are theoretical 8 . The variations between the SEE yields can be shown by the first crossover energy, i.e.…”

Section: B Materials' Samplesmentioning

confidence: 99%

Plasma sheath material induced dependence due to secondary electron emission

et al. 2020

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“…Based on previous findings of anomalous high secondary electron emission (SEE) of lithium surfaces exposed to a plasma [33], experiments were performed to bias the LLL [34], a C limiter and a solid lithium electrode, in order to test heat handling characteristics and the impact of injected currents on plasma performance while inserting the biased elements rather deeply into the plasma edge, which is not possible with other materials. Spontaneous currents develop at the plasma periphery when a C and a Li limiter are inserted at the same radial location, as a consequence of the very different SEE coefficients of both materials.…”

Section: Power Exhaust Physicsmentioning

confidence: 99%

Transport, stability and plasma control studies in the TJ-II stellarator

Sánchez¹,

Alegre²,

Alonso³

et al. 2015

Nucl. Fusion

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The main TJ-II results since 2012 are presented in this overview. Impurity confinement is studied showing an isotopic dependence of impurity confinement time, asymmetries in parallel impurity flows in TJ-II ion-root plasmas and impurity density asymmetries within a flux surface. In addition, first observations of electrostatic potential variations within the same magnetic flux surface are presented. Evidence of the impact of three-dimensional magnetic structures on plasma confinement and L-H transitions is also presented. The leading role of the plasma turbulence is emphasized by the observed temporal ordering of the limit cycle oscillations at the L-I-H transition. Comparative studies between tokamaks and stellarators have provided direct experimental evidence for the importance of multi-scale physics to unravel the impact of the isotope effect on transport. Novel solutions for plasma facing components based on the recently installed Li-liquid limiters (LLLs) have been developed on TJ-II, showing the self-screening effect of evaporating liquid lithium, protecting plasma-facing components against heat loads, and tritium inventory control. Regarding plasma stability, magnetic well scan experiments show that traditional stability criteria, on which

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“…Previous investigations have measured and calculated the total SEE yield from smooth polycrystalline W as a function of incident energy [25][26][27][28][29][30][31][32][33][34][35][36] and angle. 36 However, quantitative values of the total SEE yield from W fuzz have not been obtained prior to the effort herein.…”

mentioning

confidence: 99%

Secondary electron emission from plasma-generated nanostructured tungsten fuzz

Patino

Raitses

Wirz

2016

Applied Physics Letters

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Recently, several researchers [e.g., Yang et al., Sci. Rep. 5, 10959 (2015)] have shown that tungsten fuzz can grow on a hot tungsten surface under bombardment by energetic helium ions in different plasma discharges and applications, including magnetic fusion devices with plasma facing tungsten components. This work reports the direct measurements of the total effective secondary electron emission (SEE) from tungsten fuzz. Using dedicated material surface diagnostics and in-situ characterization, we find two important results: (1) SEE values for tungsten fuzz are 40%-63% lower than for smooth tungsten and (2) the SEE values for tungsten fuzz are independent of the angle of the incident electron. The reduction in SEE from tungsten fuzz is most pronounced at high incident angles, which has important implications for many plasma devices since in a negative-going sheath the potential structure leads to relatively high incident angles for the electrons at the plasma confining walls. Overall, low SEE will create a relatively higher sheath potential difference that reduces plasma electron energy loss to the confining wall. Thus, the presence or self-generation in a plasma of a low SEE surface such as tungsten fuzz can be desirable for improved performance of many plasma devices. Published by AIP Publishing.

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Electron-induced secondary electron emission coefficient of lithium, tungsten and stainless steel surfaces exposed to low-pressure plasmas

Cited by 23 publications

References 23 publications

Plasma sheath material induced dependence due to secondary electron emission

Plasma sheath material induced dependence due to secondary electron emission

Transport, stability and plasma control studies in the TJ-II stellarator

Secondary electron emission from plasma-generated nanostructured tungsten fuzz

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