Understanding the impact of insulating and conducting endplate boundary conditions on turbulence in CSDX through nonlocal simulations

Vaezi, Payam; Holland, C.; Thakur, Saikat Chakraborty; Tynan, G. R.

doi:10.1063/1.4980843

Cited by 11 publications

(5 citation statements)

References 38 publications

(51 reference statements)

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“…We should note that magnitude of electron temperature fluctuations is larger in the systematic uncertainty scan of density profile, mainly due to the increase in drift-wave instability with a more steepened profile and larger energy transfer from density fluctuations to electron temperature fluctuations through the adiabatic response. 15 Furthermore, we find that the plasma potential and electron temperature fluctuations have non-zero phase shift. Figure 10(b) shows power-weighted plasma potentialelectron temperature cross-phase fð/;T e Þ.…”

Section: B Floating Potential/ Fmentioning

confidence: 78%

“…We have introduced a nonlocal cold ions fluid set of equations to describe the physics of drift-wave turbulence in CSDX in an earlier publication. 15 The model evolves fluctuations of densityñ, vorticityX ¼ r ? Á ðn 0 r ?/ Þ, and electron temperatureT e , in the presence of an axially uniform background density profile, n 0 (r), and electron temperature profile, T e 0 ðrÞ, where the tilde superscript denotes the fluctuation part and 0 subscript denotes the equilibrium part of the quantities.…”

Section: Experimental Uncertaintiesmentioning

confidence: 99%

“…This work follows up on an earlier verification and physics study of CSDX simulations under different boundary conditions of insulating and conducting end plates at a fixed magnetic field. 15 The simulations in this paper used the experimental profiles and parameters of CSDX experimental with insulating endplates from Thakur et al 16 as the inputs to the model. The first key point that is addressed in this paper is the classification and linear sensitivity analysis of input parameter uncertainties to reduce the number of uncertainties needed for simulation runs (also known as uncertainty dimensionality reduction in uncertainty quantification literature).…”

Section: Introductionmentioning

confidence: 99%

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Validation study of a drift-wave turbulence model for CSDX linear plasma device

et al. 2017

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Section: B Floating Potential/ Fmentioning

confidence: 78%

Section: Experimental Uncertaintiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Validation study of a drift-wave turbulence model for CSDX linear plasma device

et al. 2017

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“…To compare with previous measurements of the instability in Aanesland et al [39], an insulating glass plate is positioned on the upstream side of the source chamber, illustrated in Figure 1 by a light blue section at Z = −31 cm. The presence of an insulating backplate ensures that all walls in the source region are floating, enforcing an insulated boundary condition upstream [41,42] leading to enhanced electron fluxes downstream. A pumping system consisting of a turbomolecular and rotary pump is used to maintain a base chamber pressure of 5 × 10 −6 Torr.…”

Section: Description Of the Experimental Setupmentioning

confidence: 99%

Characterization and Control of an Ion-Acoustic Plasma Instability Downstream of a Diverging Magnetic Nozzle

et al. 2020

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The study and control of resonant instabilities in magnetized plasmas is of fundamental interest over a wide range of applications from industrially relevant plasmas to plasma sources for spacecraft propulsion. In this work electrostatic probes were employed to measure a 4-20 kHz instability in the ion saturation current downstream of an electric double layer (DL) in an expanding helicon plasma source. The amplitude and frequency of the instability were found to vary in inverse proportion to the operating argon gas pressure (0.2-0.6 mTorr) and in direct proportion to the applied rf power (100-600 W) and applied solenoid current (3-8 A). A spatially resolved characterization of the maximum instability amplitude determined two radial maxima, corresponding to the locations of most positive radial ion density gradient. Control and inhibition of the instability were achieved through the application of a kHz voltage amplitude modulation to the 13.56 MHz radio-frequency (rf) power supplied to the helicon antenna. Through the application of voltage amplitude modulations in the frequency range 2-12 kHz the instability was reduced by up to 65%, exhibiting a greater reduction at higher applied modulation frequencies. This effect is described through a variation in the radial ion density gradient via asymmetrically attenuated ion acoustic density perturbations induced by the applied voltage modulation. The application of voltage amplitude modulations has been demonstrated as a potential control mechanism for density gradient driven instabilities in magnetized plasmas.

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“…The axial boundary conditions modified radial currents and drastically changed fluctuation characteristics [74,75]. In addition, spectral sidebands, markers of parametrically driven fluctuations, have been observed in electrostatic fluctuation spectra at different RF frequencies [72].…”

Section: The Helicon Dispersion Relationmentioning

confidence: 99%

Three-Dimensional Multispecies Distribution Functions in a Plasma Boundary With an Oblique Magnetic Field

Thompson¹

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The physics of a weakly magnetized boundary region are investigated by immersing a 76.2 mm diameter stainless steel disk in a helicon plasma. The velocity distributions of ions and neutral particles are mapped in the boundary region, created in 3.6 mTorr argon gas, 650 W RF power, and magnetic field B = 0.06 T, where the magnetic field lines obliquely intersect the wall (α = 16 •). These distributions are mapped using laser induced fluorescence in three spatial (3D) and three velocity (3V) dimensions, and reveal that models neglecting any one of the velocity components omit important components of the flow field. Electrostatic probe measurements are presented and establish a typical helicon plasma discharge with electron temperature T e ≈ 4.2 eV and density n ≈ 5.5 × 10 17 m −3. In addition to the observed ion temperature, T i ≈ 0.37 eV, these measurements indicate a plasma in which the electrons are highly magnetized (the ratio of the electron cyclotron frequency to the electron collision frequency is ω ce /ν e = 2.9 × 10 3) and the ions are weakly collisional (the ratio of the ion cyclotron frequency to the ion collision frequency is ω ci /ν i = 0.5 ± 0.3). Ion drift velocity measurements are presented in the E × B direction and are compared to predictions from measured plasma potential gradients. Ion flow fields are compared to predictions from collisional fluid simulations and particle-in-cell models. These models require collisions to reproduce the ion drifts well. Neutral particle distributions are observed to be in thermal equilibrium with the chamber walls (T n ≈ 0.028 eV) and essentially non-flowing on average. Charge exchange population fractions are expected to be O(10 −2), and are too small to be resolved, but are excluded to the 5% level. "O me! O life!... of the questions of these recurring; Of the endless trains of the faithless-of cities fill'd with the foolish; Of myself forever reproaching myself, (for who more foolish than I, and who more faithless?) Of eyes that vainly crave the light-of the objects mean-of the struggle ever renew'd; Of the poor results of all-of the plodding and sordid crowds I see around me; Of the empty and useless years of the rest-with the rest me intertwined; The question, O me! so sad, recurring-What good amid these, O me, O life? Answer. That you are here-that life exists, and identity; That the powerful play goes on, and you may contribute a verse." Walt Whitman, Leaves of Grass (1892) v I want to first express my gratitude for the support of my advisor, Earl Scime, who smoothed my way to WVU and who for the last two and half years has trusted me with his lab probably more than he had reason to. He has answered annoying questions at 7 am and after midnight and was available for lunch almost every day I've been in Morgantown. That kind of face-to-face relationship building is exceptional and not lost on me. He is a mentor and a friend.

show abstract

Understanding the impact of insulating and conducting endplate boundary conditions on turbulence in CSDX through nonlocal simulations

Cited by 11 publications

References 38 publications

Validation study of a drift-wave turbulence model for CSDX linear plasma device

Validation study of a drift-wave turbulence model for CSDX linear plasma device

Characterization and Control of an Ion-Acoustic Plasma Instability Downstream of a Diverging Magnetic Nozzle

Three-Dimensional Multispecies Distribution Functions in a Plasma Boundary With an Oblique Magnetic Field

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