Real-time MSE measurements for current profile control on KSTAR

Bock, de Mfm Maarten; Aussems, D.U.B.; Huijgen, RT Ralph; Scheffer, M.; Chung, Jae-Hoon

doi:10.1063/1.4732854

Cited by 4 publications

(2 citation statements)

References 5 publications

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“…Intensive spectrum measurements done for the KSTAR tokamak also indicate that the overlap can ruin the MSE polarimetry without careful selection of the spectral region and careful beam operations [18]. Along with the measurements, the simulation of the MSE emission spectra has also been studied to determine the central wavelengths of the bandpass filters [19]. Although the components (perpendicular to the Stark electric field) are stronger in intensity than the components (parallel to the Stark field), the most red-shifted components will be measured by using the bandpass filter because these are the only components that escape from the overlap of multiple MSE spectra.…”

Section: Design Of the Filter Modulesmentioning

confidence: 99%

Status of PEM-based polarimetric MSE development at KSTAR

Chung

et al. 2014

Journal of the Korean Physical Society

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A multi-chord PEM (photo elastic modulator)-based polarimetric motional Stark effect (MSE) system is under development for the KSTAR tokamak. The conceptual design for the front optics was optimized to preserve not only the polarization state of the input light for the MSE measurements but also the signal intensity of the existing charge exchange spectroscopy (CES) system that will share the front optics with the MSE. The optics design incorporates how to determine the number of channels and the number of fibers for each channel. A dielectric coating will be applied on the mirror to minimize the relative reflectivity and the phase shift between the two orthogonal polarization components of the incident light. Lenses with low stress-birefringence constants will be adopted to minimize non-linear and random changes in the polarization through the lenses, which is a trade-off with the rather high Faraday rotation in the lenses because the latter effect is linear and can be relatively easily calibrated out. Intensive spectrum measurements and their comparisons with the simulated spectra are done to assist the design of the bandpass filter system that will also use tilting stages to remotely control the passband. Following the system installation in 2014, the MSE measurements are expected to be performed during the 2015 KSTAR campaign.

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Section: Design Of the Filter Modulesmentioning

confidence: 99%

Status of PEM-based polarimetric MSE development at KSTAR

Chung

et al. 2014

Journal of the Korean Physical Society

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“…Recently, a real-time MSE diagnostics for current profile control has been developed on KSTAR with a beam energy of ∼90 keV. [5] However, there are still some difficulties in using low magnetic field devices; for example, MAST, with the 𝐵 𝑡 = 0.5 T on which the spectral broadening is too large compared with the Stark splitting, only provides a polarization fraction below 40% in most cases. [6] HL-2A is a middle-sized tokamak with two closed divertors [7] and high fuel efficiency by supersonic molecular beam injection is its merit.…”

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confidence: 99%

The Spectral Broadening of Motional Stark Effect in the HL-2A Tokamak

Jiang¹,

Yu²,

Yan³

et al. 2013

Chinese Phys. Lett.

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The spectral broadening of motional Stark effect (MSE) is simulated in the HL-2A tokamak, which is in good agreement with the experimental observation. The divergence angle of the neutral beam, finite lens size and beam energy dissociation are the main broadening factors, while the lens size is the most important one. The experimental spectra fitted by multiple Gaussian distributions reveal that the Stark splitting and its full width at half maximum (FWHM) are ∼0.07 nm and ∼0.19 nm, respectively. Therefore, the 𝜋 and 𝜎 components of the MSE will overlap since the Stark splitting is much smaller than its spectral broadening. A narrowband filter with the FWHM of about 0.16 nm is good enough to isolate the two components for providing the polarization fraction over 50%, which guarantees reasonable measurement precision for magnetic field pitch angle.

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Real-time signal processing system based on FPGA for motional Stark effect diagnostic on EAST

Liu

Yang

et al. 2021

Review of Scientific Instruments

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The plasma current density profile plays a key role in the development of a high poloidal beta scenario, which is essential for long-pulse and high-performance plasma operation on a tokamak. Based on the polarimetry technique, a Motional Stark Effect (MSE) diagnostic has been built on the Experimental Advanced Superconducting Tokamak. To be prepared for real-time (RT) feedback control of the plasma current density profile in the future, a RT signal processing system has been developed. The RT signal processing system is composed of three functional modules: analog-to-digital conversion (ADC) module, polarization information extraction module, and digital-to-analog conversion (DAC) module. The final objective of this system is to acquire the polarization information of the MSE. Based on the field-programmable gate array unit, fast Fourier transformation is adopted to process the Photoelastic Modulator (PEM) digital signal, which was converted from a PEM signal via the ADC module. By means of frequency spectrum separation, the components around double modulating frequencies are restored through inverse fast Fourier transformation. Furthermore, the two amplitudes of their corresponding components can be obtained through a digital harmonic analyzer technique. Afterward, the ratio of the two amplitudes is calculated by arc tangent so that the polarization angle is obtained. Finally, the information of this polarization angle is converted into a voltage signal by the DAC module and then output in RT. The test results based on the RT signal processing system are in good agreement with those based on the phase lock-in amplifiers. The working cycle of this system is shorter than 10 ms, which meets the requirements of the MSE diagnostic as a RT controller. The algorithm of RT signal processing and the relevant technology applied for building this system are presented in the main body of this paper in detail.

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Real-time MSE measurements for current profile control on KSTAR

Cited by 4 publications

References 5 publications

Status of PEM-based polarimetric MSE development at KSTAR

Status of PEM-based polarimetric MSE development at KSTAR

The Spectral Broadening of Motional Stark Effect in the HL-2A Tokamak

Real-time signal processing system based on FPGA for motional Stark effect diagnostic on EAST

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