Features of edge magnetic turbulence in DIII-D expanded boundary divertor discharges

Ohyabu, N.; Osborne, T. H.; Jahns, G.L.; Strait, E.J.; Stambaugh, R.D.

doi:10.1088/0029-5515/29/3/010

Cited by 16 publications

(8 citation statements)

References 13 publications

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“…For both central and off-axis resonance near q = 1, a clear correlation between the confinement time and the fluctuation level is seen. Similar correlations of magnetic turbulence levels and improved confinement have also been observed for H-mode plasmas heated by NBI [37][38][39][40][41]. Reflectometer measurements show that these fluctuations are localized in the plasma edge [40].…”

Section: Fig 15 Calculations With the Toray Code Of Single-pass Ech A...supporting

confidence: 55%

Heating and confinement in H-mode and L-mode plasmas in DIII-D using outside launch electron cyclotron heating

et al. 1990

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Using the outside launch with vertical polarization, electron cyclotron heating (ECH) experiments in DIII-D were carried out at 60 GHz at fundamental and second harmonic frequencies. The results are consistent with wave absorption theory for accessibility. For fundamental heating with a cut-off layer between the launch location and the resonant surface, good absorption efficiency was obtained. A process for mode conversion at the wall from the extraordinary mode to the ordinary mode is postulated to explain this result. For most efficient heating it was important to avoid the presence of a locked mode. For low density plasmas at the fundamental, the global energy confinement exceeds Kaye-Goldston scaling by about a factor of 1.4. However, heating at the second harmonic agrees numerically with the Kaye-Goldston scaling formula, for ECH alone or for ECH combined with neutral beam injection (NBI), and shows a mass dependence consistent with TE ∼ √Ai. The global energy increase was insensitive to the resonance location for qres < 2–3. Comparing data at both harmonics in the low density range, where the energy confinement of Ohmic plasmas satisfies neo-Alcator density scaling and Prf/Pohm > 1, global energy confinement scales as TE ∼ Bt−0.3. Since plasma current and plasma geometry were not varied for these discharges, a scaling with safety factor q is also consistent. Using ECH alone, H-mode confinement was achieved for second harmonic heating in the central core of the plasma at a power threshold of ∼0.75 MW for plasma parameters Ip = 0.5 MA, and n̄e = 1.1 × 1019 m−3. The energy confinement times during the H-mode are similar to Ohmic values with a normalized confinement time τE/Ip ∼ 200 ms/MA. For ECH and NBI H-mode plasmas, the transition from the L-mode to the H-mode was correlated with reduced magnetic fluctuations in the divertor region. For ECH H-mode plasmas, transport analysis shows that (1) the H-mode obtained with ECH is accompanied by an improvement of the electron thermal diffusivity χe relative to the L-mode over at least part of the plasma, (2) the ion thermal diffusivity χi is larger than predicted by neoclassical theory for the L- and H-modes, and (3) χe is approximately equal to χi for the ohmically heated discharge and for the L-mode and H-mode discharges heated by ECH discussed in the paper.

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Section: Fig 15 Calculations With the Toray Code Of Single-pass Ech A...supporting

confidence: 55%

Heating and confinement in H-mode and L-mode plasmas in DIII-D using outside launch electron cyclotron heating

et al. 1990

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“…Ignoring displacement current for eo << ~r~ e and ion parallel velocity V: due to small electron-to-ion mass ratio, me/m i << 1, Ampere's law gives (5) V~A-4zn0e Ve~. In deriving (3), we have assumed 2 2 Qek• << 1, L where Qe is the electron gyroradius, k• is the perpendicular wave vector and L = I d~ In n01-1 is the density gradient scale length.…”

Section: Otv~= C (Oz~b + L Ota ) ]]Egez M E Cmentioning

confidence: 99%

Drift dissipative instabilities in hybrid frequency range

Salahuddin

Saleem

1996

Il Nuovo Cimento D

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The instabilities of electron convection mode in a collisional plasma including electromagnetic effects are investigated. It is found that all the three solutions of the linear-dispersion relation are unstable. It is shown that the ion temperature fluctuations can play a stabilizing role. An application to a typical low-temperature plasma is discussed.PACS 52.35 -Waves, oscillations, and instabilities in plasma. PACS 52.35.Kt -Drift waves.

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“…where p s -r ce (Tg/Tp 172 , L n --n eo /Un eo /3rl is the density gradient length scale and r ce is the electron gyroradius. In particular, Liewer 5 has considered the dependence of the experimentally-determined Sn e /n oe on the drift theoretical parameter p s /L n for various tokamaks. Typically one can consider Sn e /n oe » 10"3. with Mirnov ioops^ and, in very small tokamak devices, with interior magnetic probes 6 .…”

Section: Ooe L N (1)mentioning

confidence: 99%

“…Typically one can consider Sn e /n oe » 10"3. with Mirnov ioops^ and, in very small tokamak devices, with interior magnetic probes 6 . High frequency probe measurements give SB/B 0 *> 10~4-10" 5 in the interior of Microtor for u/2;t i 30 kHz, and SB/B 0 « 10~5-10" 6 at the edge of TFTR in the range 100 kHz < O>/2JI <. 150 kHz.…”

Section: Ooe L N (1)mentioning

confidence: 99%

Electromagnetic wave scattering from magnetic fluctuations in tokamaks

Vahala

Bretz

1991

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Cross sections are calculated for electromagnetic wave scattering and mode transformation from magnetic and density fluctuations in the vicinity of the principal electron cutoffs and resonances in a homogeneous plasma. For the special case of scattering perpendicular to the magnetic field, density fluctuations scatter ordinary to ordinary and extraordinary to extraordinary modes-but cannot transform these modes. On the other .hand, magnetic fluctuations

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Features of edge magnetic turbulence in DIII-D expanded boundary divertor discharges

Cited by 16 publications

References 13 publications

Heating and confinement in H-mode and L-mode plasmas in DIII-D using outside launch electron cyclotron heating

Heating and confinement in H-mode and L-mode plasmas in DIII-D using outside launch electron cyclotron heating

Drift dissipative instabilities in hybrid frequency range

Electromagnetic wave scattering from magnetic fluctuations in tokamaks

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