Low frequency fluctuations of density and potential in the peripheral plasma during ion cyclotron heating in the URAGAN-3 torsatron

Chechkin, V. V.; Григорьева, Л.И.; Nazarov, N.I.; Plyusnin, Victor F.; Shtan, A. F.; Solodovchenko, S. I.; Степанов, К.Н.; Taran, V. S.; Vojtsenya, V.S.; Voloshko, A.Yu.

doi:10.1088/0029-5515/30/11/002

Cited by 4 publications

(2 citation statements)

References 16 publications

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“…(b) Similarly to the U-3 torsatron [24], the Langmuir probes in U-3M record intense fluctuations of density (ion saturation current), E , and potential (floating potential), vp, near the boundary of the confinement region in the drift wave range of frequencies (w << w,i) with mean wavenumber N 10' m-l [25]. In particular, in the probe LP-2 location (i.e.…”

Section: Eq (3) Thatmentioning

confidence: 99%

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Density behaviour and particle losses in RF discharge plasmas of the URAGAN-3M torsatron

Chechkin¹,

Fomin²,

Григорьева³

et al. 1996

Nucl. Fusion

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URAGAN-3M (U-3M) is an l=3, m=9 torsatron with R0=1 m, ā ≈ 12 cm and ϵ(ā) ≈ 0.4. The entire magnetic system is enclosed in a large vacuum chamber and there is no material limiter, so that an open helical divertor is realized in this device. A plasma is RF produced in 100% hydrogen gas and heated in the multimode Alfven resonance regime (ω ≲ ωci) at a continuous working gas leak-in. With an RF power of ~200 kW at B = 0.45 T, a quasi-steady (up to 50 ms) state of the plasma parameters sets in with n̄e ≃ 2 × 1018 m-3, Ti(0) ≃ 130 eV and Te(0) equivalent to 300 eV. By using microwaves and Langmuir probes, the time and space behaviours of the electron density/ion saturation current are studied in the confinement volume, near the boundary of the confinement region, and in the divertor flux region. On the basis of ion saturation current profile measurements near the boundary of the confinement region the values of local particle flux density across the boundary are estimated: Γ⊥ ≈ 7 × 1020 m-2.s-1 far from the antenna and Γ⊥ approximately=1021 m-2.s-1, Γ⊥ ≈ 2 × 1021 m-2.s-1 near the antenna. Such flux densities and the corresponding diffusion coefficients are anomalously high, exceeding the neoclassical values by 2 to 3 orders of magnitude. On the other hand, these values are comparable with the flux densities and diffusivities obtained in edge plasma with similar parameters on other stellarators under NBI and ECR heating conditions. Therefore, it is claimed that the method of plasma heating that has been chosen in U-3M does not result in any substantial deterioration of particle confinement (with the possible exception of the region close to the antenna) as against other methods. Presumably, the anomalous particle transport across the boundary in U-3M is caused by destruction of magnetic surfaces and/or electrostatic drift wave turbulence. It is found that increasing the RF power results in an increase of the diverted plasma flow and of the hydrogen consumption necessary to maintain the average plasma density at a given level. This is considered as a manifestation of a common regularity, according to which particle losses grow with heating power, this effect having been observed recently on a stellarator type device under NBI and ECR heating conditions. An effect specific to U-3M, the increase of the average electron density, being observed within 1 to 2 ms after RF pulse termination, is attributed mainly to particle transport reduction due to plasma cooling, while the intensity of neutral particle ionization still remains sufficiently high in the confinement volume at the initial phase of cooling under continuous hydrogen leak-in conditions.

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Section: Eq (3) Thatmentioning

confidence: 99%

“…. the antenna owing to parametric drive of drift waves by regular electrostatic pump oscillations generated by the antenna [24].…”

Section: Eq (3) Thatmentioning

confidence: 99%

Density behaviour and particle losses in RF discharge plasmas of the URAGAN-3M torsatron

Chechkin¹,

Fomin²,

Григорьева³

et al. 1996

Nucl. Fusion

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Nonlinear theory of ion cyclotron decay instability

Mikhailenko¹,

Степанов²

1992

Phys. Scr.

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The interaction between waves in the ion cyclotron range of frequencies and the plasma boundary

Noterdaeme

Oost

1993

Plasma Phys. Control. Fusion

109

145

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The interaction beween the ion cyclotron resonance heating and the plasma edge is a vast and interlinked domain: the edge affects the radio frequency heating and the radio kquency heating &cts the edge. This interaction between the radio frequency heating and the edge is-in view of the relation behveen the edge and overall plasma properties and performance--of utmost importance. The paper gives an overview of the topic, emphasizing basic mncepis and recent results. The identification of the sheath rectification mechanism as the main cause for the influence of the RF on the edge, has permitted a better understanding of this domain and significant progress in the avoidance of the effects.

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Low frequency fluctuations of density and potential in the peripheral plasma during ion cyclotron heating in the URAGAN-3 torsatron

Cited by 4 publications

References 16 publications

Density behaviour and particle losses in RF discharge plasmas of the URAGAN-3M torsatron

Density behaviour and particle losses in RF discharge plasmas of the URAGAN-3M torsatron

Nonlinear theory of ion cyclotron decay instability

The interaction between waves in the ion cyclotron range of frequencies and the plasma boundary

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