Measurement and Modelling of Electric Potential in the Tj-Ii Stellarator

Melnikov, A. V.; Dyabilin, K. S.; Eliseev, L.G.; Лысенко, С. Е.; Dnestrovskij, Yu. N.

doi:10.21517/0202-3822-2011-34-3-54-73

Cited by 9 publications

(10 citation statements)

References 17 publications

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“…A large density range ne = (0.3-4.5) × 10 19 m −3 was explored [33,34]. The models of [33,34], including both symmetrical (tokamak-like) and asymmetrical (stellarator) parts for the particle fluxes, satisfactorily explain the E r values and trends in the core plasma in the whole plasma electron density and temperature domain, obtained so far in TJ-II. The electron root solution of the ambipolarity equation dominates for low-density ECRH plasmas.…”

Section: Electric Potential Profile In Ecr-and Nbi-heated Plasmas In ...mentioning

confidence: 72%

Plasma potential and turbulence dynamics in toroidal devices (survey of T-10 and TJ-II experiments)

Melnikov

Hidalgo²,

Eliseev

et al. 2011

Nucl. Fusion

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A direct comparison of the electric potential and its fluctuations in the T-10 tokamak and the TJ-II stellarator is presented for similar plasma conditions in the two machines, using the heavy ion beam probe diagnostic. We observed the following similarities: (i) plasma potentials of several hundred volts, resulting in a radial electric field E r of several tens of V cm−1; (ii) a negative sign for the plasma potential at central line-averaged electron densities larger than , with comparable values in both machines, even when using different heating methods; (iii) with increasing electron density n e or energy confinement time τ E , the potential evolves in the negative direction; (iv) with electron cyclotron resonance heating and associated increase in the electron temperature T e, τ E degrades and the plasma potential evolves in the positive direction. We generally find that the more negative potential and E r values correspond to higher values of τ E . Modelling indicates that basic neoclassical mechanisms contribute significantly to the formation of the electric potential in the core. Broadband turbulence is suppressed at spontaneous and biased transitions to improved confinement regimes and is always accompanied by characteristic changes in plasma potential profiles. Various types of quasi-coherent potential oscillations are observed, among them geodesic acoustic modes in T-10 and Alfvén eigenmodes in TJ-II.

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Section: Electric Potential Profile In Ecr-and Nbi-heated Plasmas In ...mentioning

confidence: 72%

Plasma potential and turbulence dynamics in toroidal devices (survey of T-10 and TJ-II experiments)

Melnikov

Hidalgo²,

Eliseev

et al. 2011

Nucl. Fusion

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“…Here we show the results of the NC simulations for four machines with simple analytical model [16]. It is based on the tailored long mean free path (lmfp) [17] and plateau [18][19][20] collisional regimes for the ion and electron fluxes like with the simple smoothing function …”

Section: Neoclassical Modeling Of the Electric Potential Profilesmentioning

confidence: 99%

Plasma Potential in Toroidal Devices: T-10, TJ-II, CHS and LHD

Melnikov

Hidalgo²,

Ido

et al. 2012

Plasma and Fusion Research

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Direct measurements of the electric potential ϕ, using the Heavy Ion Beam Probing, have been undertaken in the T-10 tokamak, and in the helical devices with various magnetic topology: TJ-II, CHS and LHD. L-mode plasmas were considered. Despite the large differences in machine sizes, heating methods and the topology of the magnetic field, the observed ϕ shows the striking similarities: (i) Similar magnitudes of E r ; (ii) For low densities, n e < 0.5 × 10 19 m −3 , ϕ is positive, and an increase in n e is associated with the decrease of positive ϕ and formation of a negative E r ; (iii) For higher densities, n e > (0.5-1) × 10 19 m −3 , both ϕ and E r tends to be negative despite the use of different heating methods: Ohmic and ECR heating in T-10, ECRH and/or NBI in TJ-II, CHS and LHD; (iv) Application of ECRH, causing a rise in T e , results in more positive values for ϕ and E r . The analysis show that the main features of the ϕ dependences on the n e and T e agree with neoclassical predictions on the four devices within experimental and simulation precisions.

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“…The neoclassical (NC) modelling, using simple analytical models [24,45] and more advanced neoclassical orbit Monte-Carlo code VENUS + δf [46] and drift kinetic code DKES with the momentum correction [47] shows that core potential is described by NC collisional mechanisms in T-10 [24,48]. In TJ-II the measured radial electric field (E r ) can be in good quantitative agreement with NC calculations [24,[49][50][51] although in some cases NC calculations overestimate E r [49].…”

Section: Plasma Potential Profilesmentioning

confidence: 97%

“…Modelling indicates that helically trapped particles, providing the asymmetric part of the particle flux, play an important role in the long mean free path regime at very low density in TJ-II [45]. When n e > 10 19 m −3 , a transition to the plateau collisional regime takes place, and a symmetrical tokamaklike transport dominates.…”

Section: Plasma Potential Profilesmentioning

confidence: 99%

Heavy ion beam probing—diagnostics to study potential and turbulence in toroidal plasmas

et al. 2017

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Heavy ion beam probing (HIBP) is a unique diagnostics to study the core plasma potential and turbulence. Advanced HIBPs operate in the T-10 tokamak and TJ-II flexible heliac with fine focused (<1 cm) and intense (100 µA) beams. They provide measurements in the wide density interval n e = (0.3-5) × 10 19 m −3 , in a wide range of Ohmic and electron cyclotron resonance heated (ECRH) discharges with various currents at T-10, and in the wide range of magnetic configurations with ECR and neutral beam injection (NBI) heating at TJ-II. Time evolution of the radial profiles and/or local values of plasma parameters from high field side (HFS) to low field side (LFS), −1 < ρ < 1, is observed in TJ-II by 125 keV Cs + ions in a single shot, while LFS (+0.2 < ρ < 1) is observed in T-10 by 300 keV Tl + ions. Multi-slit energy analyzers provide simultaneously data on the plasma potential ϕ (by the beam extra energy), plasma density n e (by the beam current), poloidal magnetic field B pol (by the beam toroidal shift), poloidal electric filed E pol that allows one to derive the electrostatic turbulent particle flux Γ E×B . The cross-phase of density oscillations produces the phase velocity of their poloidal propagation or rotation; also it gives the poloidal mode number. Dual HIBP, consisting of two identical HIBPs located ¼ torus apart provide the long-range correlations of core plasma parameters. Low-noise high-gain electronics allows us to study broadband turbulence and quasi-coherent modes like geodesic acoustic modes and Alfvén eigenmodes.

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Measurement and Modelling of Electric Potential in the Tj-Ii Stellarator

Cited by 9 publications

References 17 publications

Plasma potential and turbulence dynamics in toroidal devices (survey of T-10 and TJ-II experiments)

Plasma potential and turbulence dynamics in toroidal devices (survey of T-10 and TJ-II experiments)

Plasma Potential in Toroidal Devices: T-10, TJ-II, CHS and LHD

Heavy ion beam probing—diagnostics to study potential and turbulence in toroidal plasmas

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