Recent development of collective Thomson scattering for magnetically confined fusion plasmas

Nielsen, S. K.; Michelsen, Poul; Hansen, S. K.; Korsholm, S. B.; Leipold, F.; Rasmussen, Jesper; Salewski, M.; Schubert, M.; Stejner, M.; Stöber, J.; Wágner, D.

doi:10.1088/1402-4896/92/2/024001

Cited by 30 publications

(35 citation statements)

References 47 publications

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“…Warmray has been used extensively for the design and interpretation of CTS experiments at TEXTOR and ASDEX Upgrade (e.g. [25]), providing reliable predictions of the orientation, width, and temporal evolution of microwave beams in numerous CTS experiments. Being a raytracing code, it can only give an approximate description of the beam shape by tracing multiple peripheral rays.…”

Section: Raytracing In An Optically Thin Plasma With Wall Reflectionsmentioning

confidence: 99%

Modeling the electron cyclotron emission below the fundamental resonance in ITER

Rasmussen

Stejner

Figini

et al. 2019

Plasma Phys. Control. Fusion

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The electron cyclotron emission (ECE) in fusion devices is nontrivial to model in detail at frequencies well below the fundamental resonance where the plasma is optically thin. However, doing so is important for evaluating the background for microwave diagnostics operating in this frequency range.Here we present a general framework for estimating the ECE levels of fusion plasmas at such frequencies using ensemble-averaging of rays traced through many randomized wall reflections. This enables us to account for the overall vacuum vessel geometry, self-consistently include cross-polarization, and quantify the statistical uncertainty on the resulting ECE spectra. Applying this to ITER conditions, we find simulated ECE levels that increase strongly with frequency and plasma temperature in the considered range of 55-75 GHz. At frequencies smaller than 70 GHz, we predict an X-mode ECE level below 100 eV in the ITER baseline plasma scenario, but with corresponding intensities reaching keV levels in the hotter hybrid plasma scenario. Benchmarking against the SPECE raytracing code reveals good agreement under relevant conditions, and the predicted strength of Xmode to O-mode conversion induced by wall reflections is consistent with estimates from existing fusion devices. We discuss possible implications of our findings for ITER microwave diagnostics such as ECE, reflectometry, and collective Thomson scattering.

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Section: Raytracing In An Optically Thin Plasma With Wall Reflectionsmentioning

confidence: 99%

Modeling the electron cyclotron emission below the fundamental resonance in ITER

Rasmussen

Stejner

Figini

et al. 2019

Plasma Phys. Control. Fusion

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“…This requirement can also be fulfilled by frequency locking of the gyrotron complex by an external, highly stable, moderate‐power master source. Finally, highly stable gyrotrons are required for modern plasma diagnostic based on the method of collective Thomson scattering . Operating frequencies of such devices used in existent and developed plasma facilities should be in the range from 140 to 300 GHz …”

Section: Introductionmentioning

confidence: 99%

“…Finally, highly stable gyrotrons are required for modern plasma diagnostic based on the method of collective Thomson scattering. 15 Operating frequencies of such devices used in existent and developed plasma facilities should be in the range from 140 to 300 GHz. 16 Part of aforementioned cases can be addressed by development of MW-class device with direct frequency control; however, creation of such system meets a number of difficulties, such as lower speed due to big capacitance of the tube and diode type of electron gun in some MW-class gyrotrons.…”

Section: Introductionmentioning

confidence: 99%

Design of master oscillator for frequency locking of a complex of megawatt level microwave sources

Денисов

Kuftin

Мануилов

et al. 2020

Micro & Optical Tech Letters

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We present the results of the development of a highly stable gyrotron (with long‐term stability of an operating frequency of 170 GHz being equal to 10−9) for experiments on frequency locking and control of megawatt power sources. The electron‐optical and electrodynamic systems of the gyrotron are calculated and optimized, including the magnetron‐injection gun, interaction space, collector, and quasioptical converter of radiation into a Gaussian wave beam. Main requirements for such systems are described along with their specific features, which allow one to develop a relatively simple, low cost, and reliable master generator for synchronization of a large number of continuous‐wave megawatt gyrotrons. This reveals new possibilities for creation of gyrotron complexes capable of generation coherent radiation of nearly unlimited power levels.

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“…As the dispersion relations of the involved waves are known, this has allowed investigation of various properties of the ionosphere, such as the magnetic field, 6 conditions for electron acceleration, 7 the electron temperature, 8 the ion composition, 9 and pump-generated plasma layers. 10 PDIs in the EC frequency range have also been observed in a number of laboratory plasmas, including low-temperature experiments, [15][16][17][18] inertial confinement fusion experiments, 4 and magnetic confinement fusion experiments both in tokamaks [19][20][21][22][23][24][25][26] and in stellarators. [27][28][29][30][31] PDIs in laboratory plasmas have been used to demonstrate the occurrence of O-X-B heating, 22,28,29 to provide direct heating, 4,[16][17][18]20,21,27,30 and can also deliver information about the plasma parameters, 15,19,[23][24][25][26]31 but have generally been ignored when computing ECR heating and current drive characteristics.…”

Section: Introductionmentioning

confidence: 99%

Power threshold and saturation of parametric decay instabilities near the upper hybrid resonance in plasmas

et al. 2019

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Parametric decay instabilities (PDIs) occur for large-amplitude waves in quadratically nonlinear media, where they provide a limit of validity of linear theories and allow efficient coupling between different, well-defined wave modes. We investigate PDIs near the upper hybrid resonance in plasmas by injection of high-power electron cyclotron (EC) waves at the ASDEX Upgrade tokamak. Our measurements of PDIs have an unprecedented frequency resolution, far below the ion cyclotron frequency, allowing the first observations of secondary and tertiary PDIs during the saturation phase in a controlled laboratory setting. Furthermore, we are for the first time able to systematically compare theoretical predictions of the EC wave power thresholds, which must be exceeded to excite such PDIs, to experimental observations, validating the theory. Our findings are relevant for EC wave heating and current drive in tokamaks and stellarators, including future fusion power plants, as well as in low-temperature laboratory and industrial plasmas, inertial confinement fusion, and ionospheric modification experiments.

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Recent development of collective Thomson scattering for magnetically confined fusion plasmas

Cited by 30 publications

References 47 publications

Modeling the electron cyclotron emission below the fundamental resonance in ITER

Modeling the electron cyclotron emission below the fundamental resonance in ITER

Design of master oscillator for frequency locking of a complex of megawatt level microwave sources

Power threshold and saturation of parametric decay instabilities near the upper hybrid resonance in plasmas

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