Browsing by Author "Sharma, Sarveshwar"

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Effect of Reconstruction Scheme on the Plasma Fluid Modeling With Original and Reformulated Ion-Related Modeling Equations Using HLL Flux Scheme
(2019-02-01)
Chen, Kuan-Lin
;
Tseng, Meng-Fan
;
Gu, Bi-Ren
;
Sharma, Sarveshwar
;
Wu, Jong-Shinn
In this paper, we would like to investigate the effect of spatial reconstruction schemes on the plasma fluid model with original and reformulated ion-related modeling equations by using the Harten-Lax-van Leer (HLL) flux scheme. The results based on the 1-D fluid model equations for electropositive plasma show that the appearance of unphysical oscillations near-sheath edges strongly depends on the reconstruction schemes (e.g., kappa = 1/2, 1/3, and first-order scheme) when the original ion equations utilize the incorrect ion sound speed. The unphysical oscillations disappear no matter what the spatial reconstruction scheme is applied if the reformulated ion equations with correct ion sound speed are used instead. For electronegative plasma, the kappa reconstruction scheme causes numerical instability when using either the incorrect or correct numerical ion sound speed, but the min-mod reconstruction scheme does not. The numerical results show that for either electropositive or electronegative discharges, both the second-order HLL scheme with min-mod reconstruction and the first-order HLL schemes can produce stable solution, while the accuracy of the former is slightly better than the later. Finally, some examples with an extension to the 2-D-axisymmetric electropositive and electronegative plasmas are demonstrated.
Electric field filamentation and higher harmonic generation in very high frequency capacitive discharges
(2019-09-04)
Sharma, Sarveshwar
;
Sirse, N.
;
Sen, A.
;
Wu, J. S.
;
Turner, M. M.
The effects of the discharge voltage on the formation and nature of electric field transients in a symmetric, collisionless, very high frequency, capacitively coupled plasma are studied using a self-consistent particle-in-cell (PIC) simulation code. At a driving frequency of 60 MHz and 5 mTorr of argon gas pressure, the discharge voltage is varied from 10 V to 150 V for a fixed discharge gap. It is observed that an increase in the discharge voltage causes filamentation in the electric field transients and to create multiple higher harmonics in the bulk plasma. Correspondingly, higher harmonics, up to 7th harmonic, in the discharge current are also observed. The power in the higher harmonics increases with a rise in the discharge voltage. The plasma density continues to increase with the discharge voltage but in a nonlinear manner, whereas, the bulk electron temperature decreases. Meanwhile, the electron energy distribution function evolves from a Maxwellian at lower discharge voltages to a bi-Maxwellian at higher discharge voltages.