Pedestal magnetic turbulence measurements in ELMy H-mode DIII-D plasmas by Faraday-effect polarimetry

Chen, J.; Brower, D. L.; Ding, W. X.; Yan, Z.; Curie, M.; Kotschenreuther, M.; Osborne, T.H.; Strait, E. J.; Hatch, D. R.; Halfmoon, Michael; Mahajan, S. M.; Xiang, Jian

doi:10.1063/5.0039154

Cited by 22 publications

(39 citation statements)

References 33 publications

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“…Recently on DIII-D, the implementation of a new Faraday-effect polarimetry measurement has allowed for the measurement of highfrequency magnetic turbulence in the pedestal region [29]. These results were shown to be consistent with high-n MTM fluctuations, helping to establish the experimental existence of MTMs [26,30]. On JET, detailed comparisons with gyrokinetic simulations showed that experimentally-observed frequency bands in magnetic fluctuations were consistent with expectations from MTMs and that MTM fluctuations produce experimentally-relevant transport [25].…”

Section: Introductionmentioning

confidence: 86%

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

et al. 2021

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In a series of discharges on the DIII-D tokamak, fast vertical plasma jogs are used to induce current perturbations in the steep gradient region of the H-mode edge. These current perturbations directly influence the edge q profile, decoupling the resonant location and instability drive of pedestal-localized microtearing modes (MTMs). By exploiting this effect, we develop and apply a new experimental technique to track the dynamical frequency evolution of MTMs in the pedestal region, providing a compelling validation of the MTM model. The frequency of potential MTMs is calculated as the Doppler-shifted electron diamagnetic frequency at rational q = m/n surfaces, showing remarkable agreement with chirped frequency behavior of n = 3, 4 and 5 modes detected with fast magnetics. Data is collected throughout multiple ELM cycles in order to build robust statistics describing the time-dependent frequency evolution of MTMs, which can be explained by examining the recovery of pedestal gradients after an ELM event. MTMs have a dominant transport contribution in the electron thermal channel, so the presented results indicate that reduced models of pedestal transport must be electromagnetic in nature and constructed with accurate calculations of MTM stability; inclusion of this physics is essential for accurate predictions of the electron temperature pedestal profile. Supporting measurements of mode saturation, propagation direction and transport fingerprints are made to support the dynamic frequency determination, unambiguously and experimentally identifying MTMs in the pedestal region of DIII-D.

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Section: Introductionmentioning

confidence: 86%

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

et al. 2021

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“…It should be mentioned that the power level from B is much lower than ñ for typical tokamak parameters. The relative magnetic fluctuation level B/B is from about 10 −4 to 10 −6 measured with typical tokamak parameter [4,16]. So the expected relative fluctuation level B/B 2 /| ñ/n| 2 ∼ 10 −2 -10 −5 [4,16,18,25].…”

Section: Jinst 17 C02025 4 Polarization Rejectormentioning

confidence: 90%

“…The relative magnetic fluctuation level B/B is from about 10 −4 to 10 −6 measured with typical tokamak parameter [4,16]. So the expected relative fluctuation level B/B 2 /| ñ/n| 2 ∼ 10 −2 -10 −5 [4,16,18,25]. As mentioned in reference [13,16], the scattered power from magnetic fluctuation P CPS ∝ ( B/B) 2 , and the scattered power from electron density fluctuation P DBS ∝ ( ñ/n) 2 .…”

Section: Jinst 17 C02025 4 Polarization Rejectormentioning

confidence: 99%

“…The gyrokinetic theories predict that as the plasma β (the ratio of volume-averaged plasma pressure p to magnetic pressure B 2 /2μ 0 ) increased, the electromagnetic turbulence can be dominant and drive significant anomalous transport [1]. It is found that magnetic turbulence can influence plasma confinement [2], pedestal dynamics [3], and edge-localized modes evolution [4] in experiments. In addition, the nonlinear gyro-kinetic simulation indicates that the electromagnetic turbulence, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…The magnetic fluctuation B measurement can provide experimental verification of the theory and model of magnetic turbulence [7], especially in high beta plasma. In tokamak plasma, the magnetic fluctuation is typically measured by magnetic coils [3], motional stark effect (MSE) [8], polarimetry [4,9], etc. .…”

Section: Introductionmentioning

confidence: 99%

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Design of the cross-polarization scattering diagnostic on the HL-2A tokamak

Tong¹,

Zhong²,

Wen³

et al. 2022

J. Inst.

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A new cross-polarization scattering (CPS) diagnostic has been developed on HL-2A, which aims to measure the local magnetic fluctuation inside the plasma. It is based on the scattering of an incident microwave beam into the perpendicular polarization by magnetic fluctuations. The CPS diagnostic has been designed in the Q-band (33–50 GHz), which consists of the electronic system, quasi-optical, and polarization rejector. The ray-tracing code is used to simulate the propagation of the probe and scattered rays. To test the performance of the quasi-optical system, a 3D test platform is built and detailed test results are shown. Two methods are developed for polarization rejector on HL-2A: wire grid polarizer and dual-polarized horn antenna (DPHA). The laboratory test result shows that the polarization rejection of both methods is better than 30 dB, which meets the needs for magnetic fluctuation detection. In the future, the CPS diagnosis will be used to study the electromagnetic turbulence behavior in the high-performance plasma of the HL-2A tokamak.

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Ion thermal transport in the H-mode edge transport barrier on DIII-D

et al. 2022

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The power balance ion heat flux in the pedestal region on DIII-D increases and becomes increasingly anomalous (above conventional neoclassical) in experiments with higher temperature and lower density pedestals where the ion collisionality (νi*) is lowered toward values expected on ITER. Direct measurements of the main-ion temperature are shown to be essential on DIII-D when calculating the ion heat flux due to differences between the temperature of D+ and the more commonly measured C6+ impurity ions approaching the separatrix. Neoclassical transport calculations from NEO and non-linear gyrokinetic calculations using CGYRO are consistent with these observations and show that while neoclassical transport plays an important role, the turbulent ion heat flux due to ion scale electrostatic turbulence is significant and can contribute similar or larger ion heat fluxes at lower collisionality. Beam emission spectroscopy and Doppler backscattering measurements in the steep gradient region of the H-mode pedestal reveal increased broadband, long-wavelength ion scale fluctuations for the low νi* discharges at the radius where the non-linear CGYRO simulations were run. Taken together, increased fluctuations, power balance calculations, and gyrokinetic simulations show that the above neoclassical ion heat fluxes, including the increases at lower νi*, are likely due to weakly suppressed ion scale electrostatic turbulence. These new results are based on world first inferred ion and electron heat fluxes in the pedestal region of deuterium plasmas using direct measurements of the deuterium temperature for power balance across ion collisionalities covering an order of magnitude from high νi* values of 1.3 down to ITER relevant νi* ∼0.1.

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Pedestal magnetic turbulence measurements in ELMy H-mode DIII-D plasmas by Faraday-effect polarimetry

Cited by 22 publications

References 33 publications

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D

Design of the cross-polarization scattering diagnostic on the HL-2A tokamak

Ion thermal transport in the H-mode edge transport barrier on DIII-D

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