Transport of fast electrons during LHCD in TS, JET, and ASDEX

Peysson, Y.

doi:10.1088/0741-3335/35/sb/021

Cited by 60 publications

(53 citation statements)

References 21 publications

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“…17,27,28 Measurements of high energy bremsstrahlung were used to isolate the response of the fast electron population due to LHCD. The timescales of fast electron analysis rely on the slowing down time, convective, and diffusive times which can be drastically different from the plasma thermal properties.…”

Section: Lh Modulation Techniques and Core Power Depositionmentioning

confidence: 99%

Lower hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

et al. 2016

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For the first time, the power deposition of lower hybrid RF waves into the edge plasma of a diverted tokamak has been systematically quantified. Edge deposition represents a parasitic loss of power that can greatly impact the use and efficiency of Lower Hybrid Current Drive (LHCD) at reactor-relevant densities. Through the use of a unique set of fast time resolution edge diagnostics, including innovative fast-thermocouples, an extensive set of Langmuir probes, and a Ly a ionization camera, the toroidal, poloidal, and radial structure of the power deposition has been simultaneously determined. Power modulation was used to directly isolate the RF effects due to the prompt (t < s E ) response of the scrape-off-layer (SOL) plasma to Lower Hybrid Radiofrequency (LHRF) power. LHRF power was found to absorb more strongly in the edge at higher densities. It is found that a majority of this edge-deposited power is promptly conducted to the divertor. This correlates with the loss of current drive efficiency at high density previously observed on Alcator C-Mod, and displaying characteristics that contrast with the local RF edge absorption seen on other tokamaks. Measurements of ionization in the active divertor show dramatic changes due to LHRF power, implying that divertor region can be a key for the LHRF edge power deposition physics. These observations support the existence of a loss mechanism near the edge for LHRF at high density (n e > 1:0 Â 10 20 (m À3 )). Results will be shown addressing the distribution of power within the SOL, including the toroidal symmetry and radial distribution. These characteristics are important for deducing the cause of the reduced LHCD efficiency at high density and motivate the tailoring of wave propagation to minimize SOL interaction, for example, through the use of high-field-side launch. Published by AIP Publishing. [http://dx

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Section: Lh Modulation Techniques and Core Power Depositionmentioning

confidence: 99%

Lower hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

et al. 2016

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“…It must be noted, however, that D has generally been estimated to be between 0.3 and 1.0 m 2 s −1 for the suprathermals sustained by lower hybrid current drive, with the exception of JET (where an estimate of D ∼ 6-10 m 2 s −1 was given) [30]. A direct experimental measurement of the rate of transport of suprathermal electrons presents formidable difficulties, as was already documented in the long history of lower hybrid current drive experiments [30][31][32][33]. Some related studies with EC waves were reported in [34,35].…”

Section: Experimental Measurementsmentioning

confidence: 99%

Electron cyclotron current drive and suprathermal electron dynamics in the TCV tokamak

Coda

Alberti

Blanchard³

et al. 2003

Nucl. Fusion

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Electron cyclotron current drive (ECCD) is an important prospective tool for tailoring the current profile in nextstep devices. To fill the remaining gaps between ECCD theory and experiment, especially in the efficiency and localization of current drive, a better understanding of the physics of suprathermal electrons appears necessary. In TCV, the fast electron population is diagnosed by a multichordal, spectrometric hard x-ray camera and by a highfield side electron cyclotron emission radiometer. The main modelling tool is the quasilinear Fokker-Planck code CQL3D, which is equipped with a radial particle transport model. Systematic studies of fast electron dynamics have been performed in TCV with modulated or pulsed electron cyclotron power, followed by coherent averaging, in order to identify the roles of collisional relaxation and radial transport in the dynamics of the suprathermal population. A consistent picture is emerging from experiment and modelling, pointing to the crucial role of the radial transport of suprathermal electrons in the physics of ECCD.

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“…Earlier calculations of LH-driven fast electron diffusion coefficients have been deduced from experiments and modeling on Alcator C [6], PBX-M [7], Tore Supra [8,9], ASDEX [9,10], and JET [9]. These analyses yielded diffusivities ranging from 0.1 to 10 m 2 /s.…”

Section: Introductionmentioning

confidence: 99%

Investigation of lower hybrid physics through power modulation experiments on Alcator C-Mod

et al. 2011

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Lower hybrid current drive (LHCD) is an attractive tool for off-axis current profile control in magneticly confined tokamak plasmas and burning plasmas (ITER), because of its high current drive efficiency. The LHCD system on Alcator C-Mod operates at 4.6 GHz, with ∼ 1 MW of coupled power, and can produce a wide range of launched parallel refractive index (n || ) spectra. A 32 chord, perpendicularly viewing hard x-ray camera has been used to measure the spatial and energy distribution of fast electrons generated by LH waves. Square-wave modulation of LH power on a time scale much faster than the current relaxation time does not significantly alter the poloidal magnetic field inside the plasma and thus allows for realistic modeling and consistent plasma conditions for different n || spectra. Inverted hard x-ray profiles show clear changes in LH-driven fast electron location with differing n || . Boxcar binning of hard x-rays during LH power modulation allows for ∼ 1 ms time resolution, which is sufficient to resolve the build-up, steady-state, and slowing-down phases of fast electrons. Ray-tracing/Fokker-Planck modeling in combination with a synthetic hard x-ray diagnostic show quantitative agreement with the x-ray data for high n || cases. The time histories of hollow x-ray profiles have been used to measure off-axis fast electron transport in the outer half of the plasma, which is found to be small on a slowing down time scale.

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Transport of fast electrons during LHCD in TS, JET, and ASDEX

Cited by 60 publications

References 21 publications

Lower hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

Lower hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

Electron cyclotron current drive and suprathermal electron dynamics in the TCV tokamak

Investigation of lower hybrid physics through power modulation experiments on Alcator C-Mod

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