Comparison of Doppler back-scattering and charge exchange measurements of E × B plasma rotation in the DIII-D tokamak under varying torque conditions

Pratt, Quinn; Rhodes, T. L.; Chrystal, C.; Carter, Troy

doi:10.1088/1361-6587/ac8614

Cited by 7 publications

(3 citation statements)

References 28 publications

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“…DBS is a fusion plasma diagnostic capable of measuring turbulent flow velocities [3,4], density fluctuation spectra [5], and radial correlation lengths [6]. DBS is an established diagnostic used on tokamaks and stellarators around the world [4,[7][8][9][10].…”

Section: Dbs Background and Theorymentioning

confidence: 99%

Density wavenumber spectrum measurements, synthetic diagnostic development, and tests of quasilinear turbulence modeling in the core of electron-heated DIII-D H-mode plasmas

Pratt,

Hall-Chen,

Neiser

et al. 2023

Nucl. Fusion

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Measurements of the turbulent density wavenumber spectrum, δ n ˆ e ( k ⊥ ) , using the Doppler Back-Scattering (DBS) diagnostic are reported from DIII-D H-mode plasmas with electron cyclotron heating as the only auxiliary heating method. These electron-heated plasmas have low collisionality, ν e ∗ < 1 , T e / T i > 1 , and zero injected torque—a regime expected to be relevant for future fusion devices. We probe density fluctuations in the core (ρ ≈ 0.7) over a broad wavenumber range, 0.5 ⩽ k ⊥ ⩽ 16 cm−1 ( 0.1 ⩽ k ⊥ ρ s ⩽ 5 ), to characterize plasma instabilities and compare with theoretical predictions. We present a novel synthetic DBS diagnostic to relate the back-scattered power spectrum, P s ( k ⊥ ) —which is directly measured by DBS—to the underlying electron density fluctuation spectrum, δ n ˆ e ( k ⊥ ) . The synthetic DBS P s ( k ⊥ ) spectrum is calculated by combining the SCOTTY beam-tracing code with a model δ n ˆ e ( k ⊥ ) predicted either analytically or numerically. In this work we use the quasi-linear code Trapped Gyro-Landau Fluid (TGLF) to approximate the δ n ˆ e ( k ⊥ ) spectrum. We find that TGLF, using the experimental profiles, is capable of closely reproducing the DBS measurements. Both the DBS measurements and the TGLF-DBS synthetic diagnostic show a wavenumber spectrum with variable decay. The measurements show weak decay (k −0.6) for k < 3.5 cm−1, with k −2.6 at intermediate-k ( 3.5 ⩽ k ⩽ 8.5 cm−1), and rapid decay (k −9.4) for k > 8.5 cm−1. Scans of physics parameters using TGLF suggest that the normalized ∇ T e scale-length, R / L T e , is an important factor for distinguishing microturbulence regimes in these plasmas. A combination of DBS observations and TGLF simulations indicate that fluctuations remain peaked at ITG-scales (low k) while R / L T e -driven TEM/ETG-type modes (intermediate/high k) are marginally sub-dominant.

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Section: Dbs Background and Theorymentioning

confidence: 99%

Density wavenumber spectrum measurements, synthetic diagnostic development, and tests of quasilinear turbulence modeling in the core of electron-heated DIII-D H-mode plasmas

Pratt,

Hall-Chen,

Neiser

et al. 2023

Nucl. Fusion

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“…where ⃗ V is the velocity of the moving turbulence in the measurement frame [34] and − → k ⊥ is the turbulence wavenumber [35]. The Doppler frequency shift ∆ω D can be extracted from the DBS measurements as the position of the 'centre of gravity' of the complex DBS signal I(t) + iQ(t) spectral density, or the phase derivative of the complex DBS signal.…”

Section: Dbs On Globus-m2mentioning

confidence: 99%

The investigation of edge-localized modes on the Globus-M2 tokamak using Doppler backscattering

Ponomarenko,

Gusev,

Kiselev

et al. 2023

Nucl. Fusion

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The first results of investigation of edge localized modes (ELMs) in the Globus-M2 tokamak using the Doppler backscattering method are presented in this paper. Specifically, ELMs that are initiated by sawtooth crashes in the H-mode are discussed. The goal of this paper is study plasma turbulence behaviour during ELMs and to showcase what ELM characteristics can be obtained using Doppler backscattering (DBS). An increase of the poloidal rotation velocity during an ELM burst and a decrease in the inter-ELM periods was observed. The effect of ELMs on the plasma turbulence was investigated and estimated to span around 6 cm inside the separatrix. This is to do with the fact that the sawtooth crashes which are responsible for initiating the ELMs take place in the core plasma. Additional experiments with standard reflectometry indicate that ELMs develop 3 cm inside the separatrix where the pedestal region is believed to be in Globus-M2. The direction of the expansion of the ELMs from the inner plasma region to the edge was determined and the velocity was estimated to be around 8 km s−1. During a single ELM burst a series of filament structures were found in the peripheral DBS channels. In an attempt to understand the processes involved modelling of the reaction of the DBS signals to filaments was done using the BOUT ++ and IPF-FD3D full-wave codes, and the cases for both linear and nonlinear scattering were considered. The results show that the presence of nonlinear scattering during ELMs can lead to an overestimation of the measured velocity values in the region of filament existence near the separatrix.

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“…Here, the term perpendicular refers to the binormal direction to the magnetic field and the flux surface normal. The phase velocity is usually small compared to the E × B-velocity, v ph ≪ v E×B [10,11] (and references therein), such that the variation of v ⊥ is mainly driven by the poloidal variation of the background magnetic field and the radial electric field E r , that varies due to flux compression via the Grad-Shafranov shift.…”

Section: Introductionmentioning

confidence: 99%

Impact of the turbulence wavenumber spectrum and probing beam geometry on Doppler reflectometry perpendicular velocity measurements

Frank

Höfler

Happel

et al. 2023

Plasma Phys. Control. Fusion

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The perpendicular propagation velocity of turbulent density fluctuations is an important parameter in fusion plasmas, since sheared plasma flows are crucial for reducing turbulence, and thus an essential input parameter for turbulent transport simulations. In the recent past various fusion devices have observed poloidal asymmetry in this velocity using Doppler and correlation reflectometry. In this work, the phase screen model is used to analytically explain and quantify the combined effect of finite wavenumber resolution due to plasma curvature and probing beam geometry in a realistic turbulence wavenumber spectrum, leading to a reduced dominantly backscattered wavenumber and a further underestimation of the perpendicular propagation velocity determined by Doppler reflectometry. The full-wave code IPF-FD3D, which simulates microwave propagation and scattering, is used as a synthetic Doppler reflectometer to study the effects of this diagnostic effect in a circular geometry using various isotropic synthetic turbulence wavenumber spectra. Angular scans from the midplane and variations in the position of the probing antenna are shown to estimate the effects of the diagnostic effect on the poloidal asymmetries.

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Comparison of Doppler back-scattering and charge exchange measurements of E × B plasma rotation in the DIII-D tokamak under varying torque conditions

Cited by 7 publications

References 28 publications

Density wavenumber spectrum measurements, synthetic diagnostic development, and tests of quasilinear turbulence modeling in the core of electron-heated DIII-D H-mode plasmas

Density wavenumber spectrum measurements, synthetic diagnostic development, and tests of quasilinear turbulence modeling in the core of electron-heated DIII-D H-mode plasmas

The investigation of edge-localized modes on the Globus-M2 tokamak using Doppler backscattering

Impact of the turbulence wavenumber spectrum and probing beam geometry on Doppler reflectometry perpendicular velocity measurements

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