A poloidal high-k scattering system for NSTX-U

2022 ◽  
Vol 17 (01) ◽  
pp. C01018
Author(s):  
C.W. Domier ◽  
J. Dannenberg ◽  
Y. Zhu ◽  
X. Liu ◽  
J.R. Sirigiri ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Far Infrared ◽  
Density Fluctuations ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Scattering System ◽  
Electron Temperature Gradient ◽  
High K ◽  
Electron Density Fluctuations ◽  
Scattering Volume

Abstract A previous 5-channel tangential high-k scattering system is being replaced by an 8-channel, poloidal high-k scattering system on the National Spherical Torus eXperiment Upgrade (NSTX-U) device located in Princeton, NJ, USA. The 693 GHz poloidal scattering system replaces a 280 GHz tangential scattering system to study high-k electron density fluctuations on NSTX-U, thereby considerably enhancing planned turbulence physics studies by providing a measurement of the k θ -spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. Two approaches to generating the 693 GHz probe beam are under development: an optically-pumped far-infrared (FIR) laser that generates ∼50 mW, and a compact gyrotron that can potentially generate in excess of 5 W. Large aperture optics collect radiation scattered from density fluctuations in the plasma core at 8 simultaneous scattering angles ranging from 2 to 15° corresponding to poloidal wavenumbers that extend to >40 cm−1. Steerable launch optics coupled with receiver optics mounted on a 5-axis receiver carriage allow the scattering volume to be placed radially from r/a = 0.3 out to the pedestal region (r/a ∼ 0.99) and translated horizontally as needed to satisfy wavenumber matching.

scholarly journals Gyrokinetic stability of electron–positron–ion plasmas

2018 ◽  
Vol 84 (1) ◽  
Author(s):  
A. Mishchenko ◽  
A. Zocco ◽  
P. Helander ◽  
A. Könies
Keyword(s):  
Dispersion Relation ◽  
Temperature Gradient ◽  
Electron Temperature ◽  
Alfven Wave ◽  
Ion Temperature ◽  
Slab Geometry ◽  
Ion Temperature Gradient ◽  
Electron Temperature Gradient ◽  
Electron Positron ◽  
Ion Proton

The gyrokinetic stability of electron–positron plasmas contaminated by an ion (proton) admixture is studied in a slab geometry. The appropriate dispersion relation is derived and solved. Stable K-modes, the universal instability, the ion-temperature-gradient-driven instability, the electron-temperature-gradient-driven instability and the shear Alfvén wave are considered. It is found that the contaminated plasma remains stable if the contamination degree is below some threshold and that the shear Alfvén wave can be present in a contaminated plasma in cases where it is absent without ion contamination.

Three electrostatic temperature drift instabilities

1981 ◽  
Vol 25 (1) ◽  
pp. 145-159 ◽  
Author(s):  
S. Peter Gary ◽  
Barbara Abraham-Shrauner
Keyword(s):  
Magnetic Field ◽  
Temperature Gradient ◽  
Electron Temperature ◽  
Lower Hybrid ◽  
Ion Temperature ◽  
Temperature Drift ◽  
Ion Temperature Gradient ◽  
Electron Temperature Gradient ◽  
Drift Instability ◽  
Electrostatic Dispersion

This paper considers temperature drift instabilities, modes which can be driven unstable solely by a temperature gradient perpendicular to a magnetic field. The linear electrostatic dispersion relation for a Vlasov plasma in a uniform magnetic field is used and propagation is assumed to be in the plane perpendicular to the gradient. Three temperature drift instabilities have been found. The ion temperature drift instability arises at frequencies much below the ion cyclotron frequency, the electron temperature drift instability propagates somewhat below that frequency and the lower-hybrid temperature drift instability has frequencies above the lower-hybrid frequency. The first of these modes is driven by an ion temperature gradient and is enhanced by increasing Te/Ti. The latter two modes are driven by an electron temperature gradient and are enhanced by a decreasing Te/Ti. Density gradients are considered as an additional source of free energy, and comparisons of temperature drift with density drift instabilities are made.

scholarly journals Enstrophy non-conservation and the forward cascade of energy in two-dimensional electrostatic magnetized plasma turbulence

2020 ◽  
Vol 86 (4) ◽  
Author(s):  
G. G. Plunk
Keyword(s):  
Temperature Gradient ◽  
Plasma Turbulence ◽  
Magnetized Plasma ◽  
Larmor Radius ◽  
Ion Temperature ◽  
Fluid System ◽  
Ion Temperature Gradient ◽  
Zonal Flows ◽  
Electron Temperature Gradient ◽  
Enstrophy Cascade

A fluid system is derived to describe electrostatic magnetized plasma turbulence at scales somewhat larger than the Larmor radius of a given species. It is related to the Hasegawa–Mima equation, but does not conserve enstrophy, and, as a result, exhibits a forward cascade of energy, to small scales. The inertial-range energy spectrum is argued to be shallower than a $-11/3$ power law, as compared to the $-5$ law of the Hasegawa–Mima enstrophy cascade. This property, confirmed here by direct numerical simulations of the fluid system, may help explain the fluctuation spectrum observed in gyrokinetic simulations of streamer-dominated electron-temperature-gradient driven turbulence (Plunk et al., Phys. Rev. Lett., vol. 122, 2019, 035002), and also possibly some cases of ion-temperature-gradient driven turbulence where zonal flows are suppressed (Plunk et al., Phys. Rev. Lett., vol. 118, 2017, 105002).

Low-frequency fluctuations in scrape-off layer of tokamak plasma with limiter biasing

2011 ◽  
Vol 77 (6) ◽  
pp. 733-748
Author(s):  
N. BISAI ◽  
RAMESWAR SINGH ◽  
R. SINGH
Keyword(s):  
Growth Rate ◽  
Temperature Gradient ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Tokamak Plasma ◽  
Equilibrium Density ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Electron Temperature Gradient ◽  
Field Mobility

AbstractThe effects of limiter biasing on the equilibrium density and potential profiles of the scrape-off layer (SOL) in tokamak plasma are investigated by including ionization and cross-field mobility. It is shown that a broadening of SOL can take place by the inclusion of ionization for low negative biasing. Various microinstabilities relevant for SOL plasmas have been studied. Generalized low-frequency dispersion relation is derived. It is shown that limiter biasing significantly modifies the SOL fluctuations. It is also shown that growth rate of conductive wall instability is smaller for negative biasing than positive biasing case. New mode, the modified Simon–Hoh, and ion temperature gradient instabilities are found to contribute significantly to the growth of curvature- and electron temperature-gradient-driven conductive wall instabilities.

scholarly journals Turbulent impurity transport simulations in Wendelstein 7-X plasmas

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
J. M. García-Regaña ◽  
M. Barnes ◽  
I. Calvo ◽  
F. I. Parra ◽  
J. A. Alcusón ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Ion Temperature ◽  
Trace Impurities ◽  
Ion Temperature Gradient ◽  
Electron Temperature Gradient ◽  
Impurity Transport ◽  
Impurity Species ◽  
Nonlinear Simulations ◽  
Electron Mode ◽  
Mode Tem

A study of turbulent impurity transport by means of quasilinear and nonlinear gyrokinetic simulations is presented for Wendelstein 7-X (W7-X). The calculations have been carried out with the recently developed gyrokinetic code stella. Different impurity species are considered in the presence of various types of background instabilities: ion temperature gradient (ITG), trapped electron mode (TEM) and electron temperature gradient (ETG) modes for the quasilinear part of the work; ITG and TEM for the nonlinear results. While the quasilinear approach allows one to draw qualitative conclusions about the sign or relative importance of the various contributions to the flux, the nonlinear simulations quantitatively determine the size of the turbulent flux and check the extent to which the quasilinear conclusions hold. Although the bulk of the nonlinear simulations are performed at trace impurity concentration, nonlinear simulations are also carried out at realistic effective charge values, in order to know to what degree the conclusions based on the simulations performed for trace impurities can be extrapolated to realistic impurity concentrations. The presented results conclude that the turbulent radial impurity transport in W7-X is mainly dominated by ordinary diffusion, which is close to that measured during the recent W7-X experimental campaigns. It is also confirmed that thermodiffusion adds a weak inward flux contribution and that, in the absence of impurity temperature and density gradients, ITG- and TEM-driven turbulence push the impurities inwards and outwards, respectively.

scholarly journals Short wavelength ion temperature gradient turbulence

2012 ◽  
Vol 19 (10) ◽  
pp. 102508 ◽  
Author(s):  
J. Chowdhury ◽  
S. Brunner ◽  
R. Ganesh ◽  
X. Lapillonne ◽  
L. Villard ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Short Wavelength ◽  
Ion Temperature ◽  
Ion Temperature Gradient
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