Laser induced fluorescence diagnostic for velocity distribution functions: applications, physics, methods and developments

Yip, Chi-Shung; Jiang, Di

doi:10.1088/2058-6272/abec62

Cited by 5 publications

(3 citation statements)

References 163 publications

(280 reference statements)

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“…This may not be easily satisfied with manual labor when maintenance personnel cannot enter the optical equipment room during and for a safety period after burning plasma operation. Even though the operation of LIF system has been greatly simplified with the employment of diode lasers [1,4], a typical external cavity diode laser (ECDL) still requires very delicate cavity alignment in two dimensions, which was generally performed by laser engineers or experienced researchers familiar with ECDL operations. Coupling into the fiber optics requires similarly delicate control.…”

Section: Unmanned Lif Diagnosticsmentioning

confidence: 99%

“…Being a non-perturbing direct measurement, laser induced fluorescence (LIF) is a powerful laseraided plasma diagnostics (LAPD). With the development of tunable (>10 GHz), narrow linewidth (<10 MHz) lasers over the past few decades, LIF is increasingly readily employed to measure ion and neutral velocity distribution functions (IVDFs/NVDFs) or energy distribution function (EDF) via sweeping the wavelength of the exciting laser to obtain the Doppler excitation spectrum of a population of metastable ions or neutrals [1,2]. By measuring the emission of laser-excited light from metastable ions or neutrals, LIF acts upon the quantum state of the measured particle and applies almost no additional electrostatic perturbation in the measurement process.…”

Section: Introductionmentioning

confidence: 99%

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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: Unmanned Lif Diagnosticsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Recent development of LIF diagnostics in ASIPP

Yip,

Jiang,

Jin

et al. 2023

J. Inst.

Self Cite

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“…Laser-induced fluorescence (LIF) of metastable ions is a non-invasive, direct measurement of the ion velocity distribution function (Yip & Jiang 2021). With more than 30 years of development, laser-induced fluorescence is becoming an increasingly common plasma diagnostics tool for measuring the velocity distribution functions of ions and neutral particles in studies of Hall thrusters (Mazouffre et al.…”

Section: Introductionmentioning

confidence: 99%

Probabilistic effect of metastable excitation on lock-in amplified plasma laser-induced fluorescence diagnostics at modulation frequencies comparable to the fluorescence frequency

Jiang

Jin²,

Yip³

et al. 2022

J. Plasma Phys.

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In this paper, effects of discharge parameters and modulation frequency on the signal of laser-induced fluorescence measurements of ion velocity distribution functions are investigated in the LIF Test Source. A maximum modulation frequency is found for each given set of parameters, beyond which the signal gradually declines. Meanwhile, this maximum modulation frequency occurred consistently at ~1/10 of the theoretical frequency limit and photon counts received by a photomultiplier tube, which indicates that as modulation frequency and the associated per-pulse-excitation-event count decrease, the transition from the macroscopic statistical signal to the microscopic probabilistic signal is a gradual process.

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A simple replacement of tungsten filament hot cathodes by DC heated LaB6 rod and its noise characteristics with laser-induced fluorescence

Jiang

Yip

Zhang

et al. 2021

Review of Scientific Instruments

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Hot cathode discharges are common plasma sources for fundamental plasma physics studies and other applications due to their quiescent and relatively simple properties, and tungsten filaments are commonly used for the ease of heating them. Recently, tungsten filaments are increasingly being replaced by less luminous alternatives, such as barium oxide or lanthanum hexaboride. These materials can emit electrons at temperatures close to 1000 K lower than tungsten, greatly reducing their blackbody radiations. This results in significant improvement in signal recovery for active spectral diagnostic, such as laser-induced fluorescence. However, these less luminous cathodes often come in vastly more complicated designs than those of tungsten hot cathodes and are much more expensive to procure and difficult to operate. In this paper, we present a simple, low cost direct current heated design of a LaB6 cathode that is manufactured at suitable dimensions and make a comparison of the laser-induced fluorescence (LIF) signal-to-noise ratio of this LaB6 hot cathode discharge with that of a typical tungsten filament discharge, revealing that LaB6 has, indeed, an improved LIF signal-to-noise ratio compared with the tungsten filament.

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Laser induced fluorescence diagnostic for velocity distribution functions: applications, physics, methods and developments

Cited by 5 publications

References 163 publications

Recent development of LIF diagnostics in ASIPP

Recent development of LIF diagnostics in ASIPP

Probabilistic effect of metastable excitation on lock-in amplified plasma laser-induced fluorescence diagnostics at modulation frequencies comparable to the fluorescence frequency

A simple replacement of tungsten filament hot cathodes by DC heated LaB6 rod and its noise characteristics with laser-induced fluorescence

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