arXiv subjects

L. M. Awasthi

Publications and source records attributed to L. M. Awasthi.

3 recordsLinked to original sources

arXiv2019

ETG Turbulence Induced Energy flux in the Large Laboratory Plasma

The Large Volume Plasma Device (LVPD) has successfully demonstrated excitation of Electron Temperature Gradient (ETG) driven turbulence in finite plasma beta condition , where the threshold condition for ETG turbulence is satisfied. The observed mode follows wave-vector scaling and frequency ordering of ETG turbulence. Simultaneous measurement of fluctuations in electron temperature, $δT_e $, plasma density, $δn_e $ and potential,$δV_f $ are obtained. Strong negative correlation with correlation coefficients $ C_{δn_e δϕ_f}\sim -0.8 $ and $ C_{δT_e δϕ}\sim -0.9 $ are observed between density and potential and temperature and potential fluctuations, respectively. These correlated density, temperature and potential fluctuations lead to generation of turbulent heat flux. The measured heat flux is compared with theoretically estimated heat flux from ETG model equations. The experimental result shows that net heat flux is directed radially outward.

physics.plasm-ph↗

arXiv2019

Observation of Electromagnetic Fluctuation Induced Particle Transport in ETG Dominated Large Laboratory Plasma

The Large Volume Plasma device(LVPD), a cylindrically shaped, linear plasma device of dimension( $ϕ=2m $, $ L =3m $) have successfully demonstrated the excitation of Electron Temperature Gradient(ETG) turbulence[ Mattoo et al.,[1]]. The observed ETG turbulence shows significant power between $ω\sim (25-90 krad/s )> Ω_{ci}(= 8 krad/s )$, corresponding to the wavenumber, $ k_y ρ_e ~ (0.1- 0.2)$ where, $ Ω_{ci}$ and $ρ_e(=5 mm ) $, ion cyclotron frequency and electron Larmor radius, respectively. The observed frequency and wave number matches well with theoretical estimates corresponding to Whistler-ETG mode. We investigated electromagnetic (EM) fluctuations induced plasma transport in high beta ( $ β\sim 0.01 - 0.4 $ ) ETG mode suitable plasma in LVPD. The radial electromagnetic (EM) electron (ion) flux ( $ Γ^{e,i}_{em} $) results primarily from the correlation between fluctuations of parallel electron current ($δJ_{\parallel ,e,i}$ ) and radial magnetic field ($ δB_r $ ). The electromagnetic particle flux is observed to be much smaller than the electrostatic particle flux,$ Γ_{em}\approx 10^{-5} Γ_{es} $ .The EM flux is small but finite contrary to the conventional slab ETG model. The electromagnetic flux is non-ambipolar. A theoretical model is obtained for the EM particle flux in straight homogeneous magnetic field geometry. The theoretical estimates are seen to compare well with the experimental observations. Sluggish parallel ion response is identified as the key mechanism for generation of small but finite electromagnetic flux.

physics.plasm-ph↗

arXiv2017

Observation of Radially Inward Turbulent Particle Flux in ETG dominated Plasma of LVPD

Radially inward turbulent particle flux is observed in the core region of target plasma of Large Volume Plasma Device(LVPD). The region satisfy conditions for ETG turbulence, i.e. threshold condition, $ η_e = L_{n_e} / L_{T_e} > 2/3 $ , where density scale length, $ L_{n_e} \sim 300 cm $ and temerature scale length, $ L_{T_e} \sim 50cm $[S.K. Mattoo et al., Phys. Rev. Lett., 108, 255007(2012)\cite{Mattoo_PRL}]. The measured flux is dominantly electrostatic ($Γ_{es} \approx 10^{5} Γ_{em}$) although the nature of the measured turbulence is electromagnetic($β\approx 0.6 $). The turbulence has been established as a consequence of electron temperature gradient (ETG) driven modes. Experimental observations of phase angle between density ($ n_e $) and potential ($ϕ$) fluctuations, $ θ_{\tilde{n}_e, \tildeϕ} $ and electrostatic particle flux, $ Γ_{es} $ shows good agreement with the corresponding theoretical estimates for ETG turbulence.

physics.plasm-ph↗