Assessment of the measurement performance of the in-vessel system of gap 6 of the ITER plasma position reflectometer using a finite-difference time-domain Maxwell full-wave code

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Using a new framework for horn antenna optimization, a first frequency-independent horn antenna for a plasma positioning reflectometer (PPR) is designed. This hardware optimization is a new approach aiming on lowering the computational complexity of PPR interpretative models able to extract profiles and fluctuations of electron density and temperature from reflectometry measurements. PPR measurements are a strong candidate to provide real-time feedback for plasma position control in long-discharge fusion tokamaks such as ITER and DEMO, which requires fast interpretative models. Reducing the computational complexity of these models is therefore critical. In this paper, ray tracing simulations in the poloidal plane are used to compare different radiation patterns and evaluate them on multiple performance criteria. An antenna shape leading to a frequency-independent far-field radiation diagram is found with the PROFUSION optimizer and a prototype of this antenna is tested against an unoptimized conical reference antenna. The ray tracing performance criteria indicate that fundamental Gaussian frequency-independent antennas perform well, albeit in general worse than same-sized frequency-dependent antennas. Furthermore, it is seen that the pyramidal ITER gap 6 antenna performs well given the spatial constraints and that more performant antennas could be used, when more space was available. The prototype testing reveals challenges in obtaining frequencyindependent characteristics within a tokamak blanket environment, which is additionally complicated by misalignment risks.

Section: Contextmentioning

confidence: 99%

On frequency-independent horn antenna design for plasma positioning reflectometers, from simulation to prototype testing

Lips¹,

Heuraux²,

Lechte³

et al. 2021

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“…The measurement performance of a multi-reflectometers positioning system is the separatrix position error as a function of the gap, Error(F = f sep , gap). It is assumed a requirement of 1 cm for the plasma positioning system, similarly to the ITER PPR [3].…”

Section: Review Of the Input Models And Measured Quantitiesmentioning

confidence: 99%

Assessment of a multi-reflectometers positioning system for DEMO plasmas

Ricardo¹,

Silva²,

Heuraux

et al. 2019

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A: Microwave reflectometry is the prime candidate to measure the DEMO plasma position and shape. DEMO will be based on a pre-defined operation scenario, allowing the optimization of the reflectometry measurements according to the expected parameters. When evaluating the system performance for the expected baseline scenario, it is essential to take into account the e ects of the plasma displacement, of the turbulence and of the MHD activity in the measurements. Therefore, the design of the DEMO plasma position reflectometer (DEMO PPR) involves the assessment of the measurement performance of di erent poloidal views, antenna assemblies, emitting angles and di erent plasma configurations. In this work we evaluate the measurement performance over 100 di erent poloidal positions of the DEMO PPR using a synthetic monostatic O-mode reflectometer. The antennas were initially aligned perpendicularly to the wall. The results show that most of the locations at the top of the machine and near the divertor are not adequate for measuring the plasma position. These locations are characterized by larger wall-plasma distances and by larger angle of incidence on the separatrix. In order to optimize the measurement performance of the system, the antennas were aligned perpendicularly to the expected separatrix position, reducing these parameters. With the exception of the locations near the divertor, this geometrical consideration improved the measurement performance for all the positions, placing them below the requirement for the plasma positioning (⇠ 1 cm). The locations near the divertor lose the signal due to the significant plasma curvature before the separatrix. We also studied the e ect of a vertical plasma displacement of z = ±5 cm in the measurements. The results show that the system is stable, fulfilling the chosen requirements. Aligning the emission perpendicularly to the separatrix proved to be a necessary condition in the optimization and stability of the DEMO PPR system.

“…This is nonetheless a common experimental setup and traditionally, in 2D simulations, the BTOR distribution is approximated by 2D MONO simulations, considering that the two 2D H-plane cuts for the Tx and Rx antennas collapse on a single 2D Tx/Rx plane. This is the approach used in ITER [4] and DEMO 2D simulations [5] and clearly is the most extreme of the 2D approximations to made. The computational cost of using a 3D code against a 2D code is confirmed by the wallclock timing of the runs.…”

Section: Jinst 14 C08004mentioning

confidence: 99%

Benchmarking 2D against 3D FDTD codes in the assessment of reflectometry performance in fusion devices

Silva¹,

Heuraux²,

Ricardo³

et al. 2019

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A: Reflectometry is foreseen in the coming generation of tokamaks such as DTT, ITER and DEMO, creating a need to predict the behavior and capabilities of these new reflectometry systems through the used of synthetic diagnostics. The FDTD time-dependent codes use to implement synthetic diagnostics are computational demanding, the reason why 2 dimensional codes (as REFMUL or REFMULF) are used. REFMUL3, a newly developed performing parallel code gives access to 3D simulations, although at a much higher cost than the 2D ones. With this work we begin a benchmark effort to assess the main differences and compromises done when using 2D versus 3D. K: Simulation methods and programs; Plasma diagnostics -interferometry, spectroscopy and imaging 1Corresponding author.