Development of laser-induced fluorescence system for diagnosis of ITER divertor plasmas

Moskalenko, I. V.; Vetrov, S. I.; Molodtsov, N.A.; Shuvaev, D. A.; Shcheglov, D. A.

doi:10.1080/1051999042000238004

Cited by 4 publications

(2 citation statements)

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“…These limitations necessitate diagnostics designs that are fundamentally risky in terms of the successful implementation of the diagnostic itself. For example, the solid angle of the collecting optics installed in a tokamak can be limited to 1 • ∼ 2 • [2,34], where in LTP devices it can be as high as > 20 • [10,13,35]. Where one expects that a tokamak device operates at a very high density (> 10 13 cm −3 ) particularly in the divertor region, which facilitate stronger LIF signal due to elevated excitation of metastable ions/neutrals, it remains important to thoroughly validate the optical design of an LIF diagnostic via both computational predictions and experimentally with demonstration platforms which emulates a divertor plasma environment.…”

Section: Access Limitation Of Tokamak Plasma Diagnosticsmentioning

confidence: 99%

Recent development of LIF diagnostics in ASIPP

Yip,

Jiang,

Jin

et al. 2023

J. Inst.

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In this article, recent research progress of laser induced fluorescence (LIF) diagnostics in ASIPP is reviewed. The fundamental goal of ASIPP's effort on the LIF diagnostics is to develop a working velocity distribution function (VDF) diagnostic to monitor helium ash removal in burning plasmas. Real-time monitoring of helium ash VDF requires consideration in radiation safety, measurement response time, and compatibility of tokamak operation, as well as ion/neutral VDFs with a temperature at possibly >20 eV. These considerations, almost unique to large-scale instruments or specifically to tokamak plasmas, require renewed research and development (R&D) efforts in optical design, automation, and expansion of laser functionality for the LIF diagnostics that were often not considered in conventional applications of the LIF diagnostics. To this end, ASIPP invested a series of research effort into the development of LIF techniques. Signal evaluation has been performed on a diagnostics-test device (LTS), and the obtained signal strength has been extrapolated to tokamak edge and divertor relevant environments with promising results. The extrapolations compared the available solid angle and plasma density between the test device and the design scenario where the LIF diagnostics will potentially be implemented in a tokamak edge and divertor plasma. The estimation neglects the higher density of energetic electrons in the edge and divertor regions, making it a conservative assessment. Automated post-DAQ processing of LIF signals using both “conventional” methods and an AI-augmented method were also explored. Both approaches yielded usable results, but the AI-trained method showed a faster response, which is advantageous for real-time plasma diagnostics. Basic mechanisms of LIF diagnostics were also explored. Specifically, the limitations of lock-in modulation was demonstrated to determine the limitation of time-resolved measurements using such methods. De-modulation and degradation of the LIF signal occurred as the modulation frequency exceeded 1/10th of the fluorescence frequency. This finding sets a practical limit of the modulation frequency up to which we can benefit from lock-in amplification. These published works along with other unpublished progress will be thoroughly discussed in this article to illustrate ASIPP's effort towards the implementation of LIF diagnostics in future tokamak devices and to promote the application of LIF diagnostics in other fields of research.

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Section: Access Limitation Of Tokamak Plasma Diagnosticsmentioning

confidence: 99%

Recent development of LIF diagnostics in ASIPP

Yip,

Jiang,

Jin

et al. 2023

J. Inst.

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“…As we see the signal ratio reveals a pronounced dependence on the chosen plasma parameters. In the case of a too high level of scattered laser light, the fluorescence from the level 3 3 S at λ = 706.5 nm (see FIGURE 1 (a)) instead of that at the laser wavelength could be used [7].…”

Section: Derivation Of the Electron Density From Laser-and Collision-mentioning

confidence: 99%

LIF Measurements on an Atomic Helium Beam in the Edge of a Fusion Plasma—possible derivation of the electron density

Krychowiak

Mertens

Schweer

et al. 2008

AIP Conference Proceedings

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Abstract. Local values of the electron density and temperature in the edge of a fusion plasma can be derived with high space and time resolution by the use of line radiation of atomic helium beams. The accuracy of this method is mainly limited by the uncertainties in the collisional-radiative model which is needed in order to obtain both plasma parameters from the measured relative intensities of atomic helium lines. Combination of a helium beam with a pulsed high-power laser provides a possibility of n e measurement which does not require a detailed knowledge of the collisional-radiative model. The method relies on resonant laser pumping of some levels and analyzing their fluorescence after the end of the laser pulse. Such measurements were already performed in low temperature plasmas with some content of atomic helium [1,2,3]. In this paper, we discuss the applicability of this method in the fusion edge plasma in the density range of 10 12 -10 13 cm -3 when exciting helium atoms with a laser at the wavelength of λ = 388.9 nm tuned to the triplet transition 2 3 S → 3 3 P o and observing the fluorescence light at the laser wavelength and at λ = 587.6 nm (3 3 D → 2 3 P o ). A first test measurement at the TEXTOR tokamak in Jülich performed by use of an excimer-pumped dye laser in connection with a thermal helium beam is shown and discussed.

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