Density profile measurements with X-mode lower cut-off reflectometry in ASDEX Upgrade

Varela, P.; Manso, M. E.

doi:10.1063/1.4732805

Cited by 6 publications

(4 citation statements)

References 7 publications

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“…12,13 Varela et al 10 discuss the use of fast swept reflectometry to measure magnetic field profiles, and this section expands on this basic approach and applies it to NSTX-U conditions. As shown in Figure 3, while the X-mode L and R cutoffs can provide density coverage from 5 × 10 16 m −3 to ∼ 1 × 10 19 m −3 , the O-mode cutoff can also provide density coverage from 4.5 × 10 17 m −3 to ∼ 9 × 10 18 m −3 .…”

Section: Possibility Of |B| Field Profile Measurementmentioning

confidence: 98%

“…10 For the ORNL HHFW SOL reflectometer on NSTX, a simple case study was performed to analyze the potential effectiveness of using multiple reflectometry mode cutoffs. For simplicity, a linear density profile, combined with a magnetic field profile from equilibrium fitting code (EFIT) for a sample NSTX discharge, was used to simulate the reflectometer response, as shown in Figure 1(a).…”

Section: Proposed Use Of X and O-mode Cutoffs For Sol Density Prmentioning

confidence: 99%

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Using X-mode L, R and O-mode reflectometry cutoffs to measure scrape-off-layer density profiles for upgraded ORNL reflectometer on NSTX-U

Lau

Wilgen

Caughman

et al. 2014

Review of Scientific Instruments

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The pre-existing ORNL scrape-off-layer (SOL) reflectometer that operated with the X-mode R-cutoff at 6-27 GHz to measure SOL density profiles on NSTX is being upgraded to be functional at the increased magnetic fields on NSTX-U spherical tokamak. Rather than increasing the operating frequencies to measure the higher X-mode R-cutoff frequencies on NSTX-U, it will be shown that the combined use of the X-mode R, L and O-mode cutoffs at 6-27 GHz can obtain the desired SOL density profiles. The potential capabilities and obstacles of this technique to measure SOL density profiles and possibly SOL magnetic field profiles on NSTX-U will be discussed.

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Section: Possibility Of |B| Field Profile Measurementmentioning

confidence: 98%

Section: Proposed Use Of X and O-mode Cutoffs For Sol Density Prmentioning

confidence: 99%

Using X-mode L, R and O-mode reflectometry cutoffs to measure scrape-off-layer density profiles for upgraded ORNL reflectometer on NSTX-U

Lau

Wilgen

Caughman

et al. 2014

Review of Scientific Instruments

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“…There are studies that focus on reflectometry with a lower cut-off frequency [13][14][15][16]. In experimental measurements on the ASDEX Upgrade [17], DIIID [18] and NSTX [19], previous attempts were made using both O-mode and X-mode upper cut-off frequencies in the process of density profile inversion, yielding an important potential to expand the measurable density radial range of reflectometry.…”

Section: Introductionmentioning

confidence: 99%

Feasibility of applying the lower cut-off frequency for the density radial coverage extension in EAST reflectometry measurement

Huang¹,

Han²,

Ye³

et al. 2022

Plasma Sci. Technol.

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The extraordinary mode (X-mode) lower cut-off frequency is proposed to be utilized in the reflectometry diagnostic on ITER for the electron density profile measurement, which is a trade-off between extreme plasma parameters and the accessible probing frequency. On the contemporary experiments, the lower cut-off frequency can be identified at the probing frequency below the electron cyclotron frequency (fce) under certain plasma conditions. We provide here, for the first time, the experimental validation of the usage of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST. The corresponding group delay of lower cut-off frequency is evolved continuously with the upper one, revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core. It is concluded that the lower cut-off frequency can be used as a supplementary to the upper one in the density profile inversion process, which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.

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“…Moreover, the use of both X-mode and O-mode cut-offs to expand the density coverage has been adopted successfully in experiments, i.e. on DIII-D and ASDEX Upgrade [6][7][8]. This work proposes a novel method, named "Inverse Profilometry", based on the solution of an electromagnetic inverse scattering problem [9,10]: it basically uses the scattering field data E s and the wave propagation model to reconstruct the shape and/or the electrical parameter distribution of the unknown scatterer permittivity (plasma density profile).…”

Section: Introductionmentioning

confidence: 99%

Preliminary evaluation of inverse scattering-based plasma-profilometry application to fusion plasmas

et al. 2022

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A new diagnostic method able to perform plasma profilometry is investigated in this work to retrieve the plasma electron density profile in front of the Ion Cyclotron Range of Frequencies (ICRF) antennas. As a reference scenario for our numerical study, the Divertor Tokamak Test (DTT [1]) ICRF antennas and plasma will be considered. Specifically, the profilometry needs to solve an inverse scattering problem, which is non-linear and ill-posed. In some recent papers [2, 3], plasma imaging profilometry in compact plasma reactors, such as the electron cyclotron ion sources (ECRIS), has been proposed and tested numerically by means of proof-of-concept examples. In particular, proper formulation of electromagnetic inverse scattering techniques have been proposed, requiring measurements of the reflection coefficient in presence of a metallic reflecting surface or, alternatively, both the reflection and transmission coefficients through two antennas facing one each other. In this paper, we would like to investigate this method also for large-size (scale-length) fusion reactors by addressing the profilometry of DTT-like plasma, assuming a very high-frequency probing regime (∼0.5 THz) for the accessibility of both O and X-modes in the DTT plasma (electron density up to 1020 m−3 and magnetic field up to 9 T). To this aim, we adopt COMSOL Wave Optics® module based on beam propagation method (or slowly varying envelope approximation) for simulating the wave propagation and to determine the probing frequencies. A proper formulation allowed to reconstruct a tiny scrape-off plasma layer, approximated as an isotropic medium, thanks to the high probing frequency.

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Density profile measurements with X-mode lower cut-off reflectometry in ASDEX Upgrade

Cited by 6 publications

References 7 publications

Using X-mode L, R and O-mode reflectometry cutoffs to measure scrape-off-layer density profiles for upgraded ORNL reflectometer on NSTX-U

Using X-mode L, R and O-mode reflectometry cutoffs to measure scrape-off-layer density profiles for upgraded ORNL reflectometer on NSTX-U

Feasibility of applying the lower cut-off frequency for the density radial coverage extension in EAST reflectometry measurement

Preliminary evaluation of inverse scattering-based plasma-profilometry application to fusion plasmas

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