Radially inward turbulent particle flux is observed in the core region of target plasma of Large Volume Plasma Device(LVPD)where electron temperature driven turbulence condition satisfied region satisfy conditions for ETG turbulence, i.e. threshold condition, η e = L ne /L Te > 2/3 , where density scale length, L ne ∼ 300cm and temerature scale length, L Te ∼ 50cm[S.K. Mattoo et al., Phys. Rev. Lett., 108, 255007(2012) 1 ]. The measured flux is dominantly electrostatic (Γ es ≈ 10 5 Γ em ) although the nature of the measured turbulence is electromagnetic(β ≈ 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, θñ e ,φ and electrostatic particle flux, Γ es shows good agreement with the corresponding theoretical estimates for ETG turbulence.
This paper reports experimental and theoretical investigations on plasma turbulence in the source plasma of a Large Volume Plasma Device. It is shown that a highly asymmetrical localized thin rectangular slab of strong plasma turbulence is excited by loss cone instability. The position of the slab coincides with the injection line of the primary ionizing energetic electrons. Outside the slab, in the core, the turbulence is weaker by a factor of 30. The plasma turbulence consists of oblique [θ=tan−1(k⊥/k||)≈87°] Quasi-Longitudinal (QL) electromagnetic whistlers in a broad band of 40kHz<f≤80 kHz with k⊥∼1.2 cm−1 and k||∼0.06cm−1. Experimental observations suggest that the primary agent for the turbulence is not driven by primary ionizing energetic electrons but by the loss cone feature in the velocity distribution of reflected energetic electrons. A magnetic mirror is formed in the Electron Energy Filter when it is energized. It is shown that it is this mirror which is responsible for both reflection of the energetic electrons and imposing loss cone feature on it. Theoretical framework is based upon Oblique whistler approximation by Sharma and Vlahos [Astrophys. J. 280, 405 (1984)] and Verkhoglyadova et al. [J. Geophys. Res. 115, A00F19 (2010)] and Quasi Longitudinal (QL) whistlers by Booker and Dyce [Radio Sci. J. Res 69D (1965)] for excitation of the plasma turbulence in the magnetosphere.
This paper describes an in-house designed large Electron Energy Filter (EEF) utilized in the Large Volume Plasma Device (LVPD) [S. K. Mattoo, V. P. Anita, L. M. Awasthi, and G. Ravi, Rev. Sci. Instrum. 72, 3864 (2001)] to secure objectives of (a) removing the presence of remnant primary ionizing energetic electrons and the non-thermal electrons, (b) introducing a radial gradient in plasma electron temperature without greatly affecting the radial profile of plasma density, and (c) providing a control on the scale length of gradient in electron temperature. A set of 19 independent coils of EEF make a variable aspect ratio, rectangular solenoid producing a magnetic field (B(x)) of 100 G along its axis and transverse to the ambient axial field (B(z) ~ 6.2 G) of LVPD, when all its coils are used. Outside the EEF, magnetic field reduces rapidly to 1 G at a distance of 20 cm from the center of the solenoid on either side of target and source plasma. The EEF divides LVPD plasma into three distinct regions of source, EEF and target plasma. We report that the target plasma (n(e) ~ 2 × 10(11) cm(-3) and T(e) ~ 2 eV) has no detectable energetic electrons and the radial gradients in its electron temperature can be established with scale length between 50 and 600 cm by controlling EEF magnetic field. Our observations reveal that the role of the EEF magnetic field is manifested by the energy dependence of transverse electron transport and enhanced transport caused by the plasma turbulence in the EEF plasma.
A capacitive coupled radio frequency (RF) plasma system has been developed for producing tungsten coated graphite tiles using plasma assisted chemical vapor deposition (PACVD) technique. To characterize the deposition chamber for optimal plasma parameters, small amount of air is released into the hydrogen plasma purposefully to measure its gas temperature using spectral bands of nitrogen molecule. Optical emission spectra in the wavelength range 350 to 900 nm have been recorded with a miniature spectrometer. Molecular spectral bands of N 2 (B 3 g -A 3 + u ) have been observed and identified as three bands from the nitrogen 1PS (Δν = 2, 3 & 4). These bands are simulated using MATLAB code developed in-house by considering Boltzmann distribution of particles in the vibrational states. The experimental spectra have been modelled with the simulated spectrum through the best-fit technique by iterating the latter one with different temperature values. Boltzmann plot method is also utilized to evaluate plasma gas temperature using identified vibrational bands. The estimated temperature using spectral modelling method matches fairly well with Boltzmann plot method. The estimated vibrational temperatures are in the range of ∼7000 -8000 K, an order higher than the room temperature ∼300 K.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.