Phaseless incoherent optical frequency domain spectroscopy

Glasser, Ziv; Zaychik, Gidon; Abramov, Rita; Gotliv, Daniel; Sternklar, Shmuel

doi:10.1364/ol.42.001848

Cited by 4 publications

(2 citation statements)

References 18 publications

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“…Consequently, the bootstrap current profile is reduced in the core and grows significantly in the pedestal, due to the higher gradients in that region, where the ohmic and NBI currents are negligible. Knowing that tearing instabilities usually occur at high beta and q 95 > 5, when the equilibrium is approaching an ideal kink limit [35,36], we performed a set of calculations with the Corsica suite [37], which includes the ideal MHD model DCON [38], to investigate the possible cause of the worsening stability of the impurity shots. In order to follow the experimental trends and isolate the impact of the different regions of the profiles, three series of profile modifications were made, increasing and decreasing the core and the pedestal separately, and one case where they were changed together.…”

Section: Mhd Stability Modellingmentioning

confidence: 99%

The physics basis to integrate an MHD stable, high-power hybrid scenario to a cool divertor for steady-state reactor operation

et al. 2023

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Coupling a high-performance core to a low heat flux divertor is a crucial step for ITER and a Fusion Pilot Plant or DEMO. Experiments in DIII-D recently expanded the steady-state hybrid scenario to high density and divertor impurity injection to study the feasibility of a radiating mantle solution. This work presents the physics basis for trade-offs between density, current drive and stability to tearing modes (TMs) at high β. EC power is crucial to tailor the plasma profiles into a passively stable state, and to eject impurities from the core. Off-axis EC depositions decrease the heating efficiency, but calculated electron heat transport coefficients show that this effect is partially mitigated by improved confinement inside the EC deposition. Additionally, the reduction in pressure is recovered by increasing the density. This favourable scaling of confinement with density was observed in high power plasmas for years, and this work provides a comprehensive explanation. ELITE predictions indicate that a path in peeling-ballooning stability opens up for certain conditions of density, power, q 95 and shaping, allowing the edge pressure to continue increasing without encountering a limit. In the core, calculated anomalous fast-ion diffusion coefficients are consistent with density fluctuation measurements in the toroidicity-induced Alfvén eigenmode range, showing that smaller fast-ion losses contribute to the enhanced confinement at high density. The edge integration study shows that divertor heat loads can be reduced with Ne and Ar injection, but this eventually triggers a cascade of n = 1, 2, 3 core TMs. We can now show that impurity radiation in the core is small and it is not the cause for the drop in confinement at high Ar and Ne injection rates. The overlap between the core TMs is consistent with the loss of pressure as estimated by the Belt model for the coupled rational surfaces. Optimization of these trade-offs has achieved plasmas with sustained H 98y2 = 1.7, f GW = 0.7 and ∼85% mantle radiation. The scenario and its variations at higher density and on- vs off-axis EC heating has been studied as a candidate for an integrated solution for several reactor designs, such as ITER, ARC, and the ARIES-ACT1 case, showing promising results in terms of fusion power and gain.

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Section: Mhd Stability Modellingmentioning

confidence: 99%

The physics basis to integrate an MHD stable, high-power hybrid scenario to a cool divertor for steady-state reactor operation

et al. 2023

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“…In the second, and following related approaches [26], the use of a reference reflector permits the interrogation using the power (phaseless) response. This second scheme provides an advantage in terms of requirements of instrumentation, since only power measurements in the RF domain are involved.…”

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confidence: 99%

Fast Incoherent OFDR Interrogation of FBG Arrays Using Sparse Radio Frequency Responses

Bellido

Peralta

Madrigal

et al. 2018

J. Lightwave Technol.

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We present two implementations of fast, discrete incoherent optical frequency-domain reflectometers (I-OFDR) for the interrogation of equally-spaced fiber Bragg grating (FBG) arrays, based on the determination of the array's radiofrequency (RF) response at a sparse number of frequencies. FBG reflectivities are determined by use of the inverse discrete Fourier transform (IDFT) of the sparse RF response, in a dynamic range limited by crosstalk induced by FBG positioning errors. The first implementation employs the complete, vector RF response at a number of frequencies equal to the number N of FBGs in the array. In the second, the introduction of a reference reflector allows for an interrogation using the power (phaseless) RF response in 4N − 1 frequencies. Demodulation based on IDFT leads to total interrogation times determined by the network analyzer scan time, which can be as low as 10 µs per FBG. Depending on the interrogation technique, electrical bandwidth requirements are 1-2 GHz in our array with 10cm separation. We implemented both techniques in a N = 10 array, inducing decays in reflectivity by 10 dB in one or several FBGs. Unambiguous detection of FBG decays was obtained in both interrogation methods. Additional tests performed on the measured reflectivities also show that measurement linearity is preserved in the 10-dB decay range. As discrete I-OFDR systems, the proposed techniques show the possibility to reach compromises between interrogation time and dynamic range or accuracy in reflectivity measurements, using the number of interrogation frequencies and the sensor topology.

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Optoelectronic chromatic dispersion and wavelength monitoring in a photodiode

et al. 2021

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The optoelectronic process of light absorption and current formation in photodiodes is shown to be a significant source of optoelectronic chromatic dispersion (OED). Simple design rules are developed for fabricating a photodiode-based dispersion device that possesses large, small, zero, and either positive or negative OED. The OED parameter is proportional to a spectrally-dependent absorption term α−1dα/dλ . Silicon-based devices are predicted to display significant OED throughout the near IR, while Ge and InGaAs have high OED in the C- and L-bands and 1650 nm region, respectively. The OED of a commercial Ge PN photodiode is measured to be 3460 ps/nm at 1560 nm wavelength with 500 kHz modulation, demonstrating 8 pm spectral resolution with the phase-shift technique. Temperature-tuning of the OED in the Ge photodiode is also demonstrated. The ubiquitous photodiode is a tunable OED device, with applications in high-resolution optical spectroscopy and optical sensing.

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Phaseless incoherent optical frequency domain spectroscopy

Cited by 4 publications

References 18 publications

The physics basis to integrate an MHD stable, high-power hybrid scenario to a cool divertor for steady-state reactor operation

The physics basis to integrate an MHD stable, high-power hybrid scenario to a cool divertor for steady-state reactor operation

Fast Incoherent OFDR Interrogation of FBG Arrays Using Sparse Radio Frequency Responses

Optoelectronic chromatic dispersion and wavelength monitoring in a photodiode

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