Compact, portable, laser induced fluorescence diagnostic for laboratory plasma sources

Paul, M.; Steinberger, Thomas; Lister, E; Arnold, N. Ivan; Artis, D.; Thakur, Saikat Chakraborty; Hall, Taylor; LeBlanc, Spencer; Scime, Earl; Thomas, Edward; Tynan, G. R.

doi:10.1063/5.0031217

Cited by 4 publications

(3 citation statements)

References 6 publications

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“…The laser is a Toptica TA 100 tunable diode laser consisting of a Littrow configuration master oscillator followed by a tapered amplifier [35] capable of generating ∼250 mW of output laser power. A small fraction of the original laser light from the master oscillator (∼3 mW) is coupled into a five-micron diameter single mode optical fiber and coupled to a Burleigh WA-1500 wavelength meter, for real-time wavelength monitoring.…”

Section: Lif Apparatusmentioning

confidence: 99%

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Ion heating in the PISCES-RF liquid-cooled high-power, steady-state, helicon plasma device

Thakur¹,

Paul²,

Hollmann³

et al. 2021

Plasma Sources Sci. Technol.

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Radio frequency (RF) driven helicon plasma sources are commonly used for their ability to produce high-density argon plasmas (n > 1019 m−3) at relatively moderate powers (typical RF power < 2 kW). Typical electron temperatures are <10 eV and typical ion temperatures are <0.6 eV. A newly designed helicon antenna assembly (with concentric, double-layered, fully liquid-cooled RF-transparent windows) operates in steady-state at RF powers up to 10 kW. We report on the dependence of argon plasma density, electron temperature and ion temperature on RF power. At 10 kW, ion temperatures >2 eV in argon plasmas are measured with laser induced fluorescence, which is consistent with a simple volume averaged 0D power balance model. 1D Monte Carlo simulations of the neutral density profile for these plasma conditions show strong neutral depletion near the core and predict neutral temperatures well above room temperatures. The plasmas created in this high-power helicon source (when light ions are employed) are ideally suited for fusion divertor plasma-material interaction studies and negative ion production for neutral beams.

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Section: Lif Apparatusmentioning

confidence: 99%

“…In section 2, we describe the experimental setup including details of the novel liquid-cooled helicon antenna assembly and the experimental device. In section 3, we describe the diagnostics, including a new, compact, portable, diode-laserbased LIF system [35]. In section 4 we present the experimental results.…”

Section: Introductionmentioning

confidence: 99%

Ion heating in the PISCES-RF liquid-cooled high-power, steady-state, helicon plasma device

Thakur¹,

Paul²,

Hollmann³

et al. 2021

Plasma Sources Sci. Technol.

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View full text Add to dashboard Cite

show abstract

“…In a companion paper [42], we show systematic scans of argon plasma density, electron temperature and ion temperature as measured by laser induced fluorescence (LIF), as well as numerically computed profiles of the argon neutral density and temperatures. We show that the RF source design is stable enough to allow us to use a novel compact portable LIF design [43], which needed several minutes of integration of the emitted light for good signal-to-noise ratios to measure the ion velocity distribution functions of argon. Having confirmed this crucial step, henceforth we always performed experiments in the PISCES-RF with the DI water coolant flowing through the ceramic cylinders.…”

Section: Effect Of DI Water On Rf Absorption and High-density Plasma ...mentioning

confidence: 99%

PISCES-RF: a liquid-cooled high-power steady-state helicon plasma device

Thakur

Simmonds

Caneses

et al. 2021

Plasma Sources Sci. Technol.

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Radio-frequency (RF) driven helicon plasma sources can produce relatively high-density plasmas (n > 1019 m−3) at relatively moderate powers (<2 kW) in argon. However, to produce similar high-density plasmas for fusion relevant gases such as hydrogen (H), deuterium (D) and helium (He), much higher RF powers are needed. For very high RF powers, thermal issues of the RF-transparent dielectric window, used in the RF source design, limit the plasma operation timescales. To mitigate this constraint, we have designed, built and tested a novel helicon plasma source assembly with a fully liquid-cooled RF-transparent window which allows steady state operations at high power (up to 20 kW) and successfully produces high-density plasma with both argon and H. Deionized (DI) water, flowing between two concentric dielectric RF windows, is used as the coolant. We show that a full azimuthal blanket of DI water does not prevent high-density plasma production. From calorimetry on the DI water, we measure the net heat removed by the coolant at steady state conditions. Using infra-red imaging, we calculate the constant plasma heat deposition and measure the final steady state temperature distribution patterns on the inner surface of the ceramic layer. The heat deposition pattern follows the helical shape of the antenna. We also show the consistency between the heat absorbed by the DI water, as measured by calorimetry, and the total heat due to the combined effect of the plasma heating and the absorbed RF. These results are being used to answer critical engineering questions for the 200 kW RF device materials plasma exposure experiment being designed at the Oak Ridge National Laboratory as a next generation plasma material interaction device.

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Wavelength modulation laser-induced fluorescence for plasma characterization

Romadanov,

Raitses,

Smolyakov

2024

Review of Scientific Instruments

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Laser-Induced Fluorescence (LIF) spectroscopy is an essential tool for probing ion and atom velocity distribution functions (VDFs) in complex plasmas. VDFs carry information about the kinetic properties of species that is critical for plasma characterization. Accurate interpretation of these functions is challenging due to factors such as multicomponent distributions, broadening effects, and background emissions. Our research investigates the use of Wavelength Modulation (WM) LIF to enhance the sensitivity of VDF measurements. Unlike standard Amplitude Modulation (AM) methods, WM–LIF measures the derivative of the LIF signal. This approach makes variations in VDF shape more pronounced. VDF measurements with WM–LIF were investigated with both numerical modeling and experimental measurements. The developed model enables the generation of both WM and AM signals, facilitating comparative analysis of fitting outcomes. Experiments were conducted in a weakly collisional argon plasma with magnetized electrons and non-magnetized ions. Measurements of the argon ion VDFs employed a narrow-band tunable diode laser, which scanned the 4p4D7/2–3d4F9/2 transition centered at 664.553 nm in vacuum. A lock-in amplifier detected the second harmonic WM signal, which was generated by modulating the laser wavelength with an externally controlled piezo-driven mirror of the diode laser. Our findings indicate that the WM–LIF signal is more sensitive to fitting parameters, allowing for better identification of VDF parameters such as the number of distribution components, their temperatures, and velocities. In addition, WM–LIF can serve as an independent method to verify AM measurements and is particularly beneficial in environments with substantial light noise or background emissions, such as those involving thermionic cathodes and reflective surfaces.

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Compact, portable, laser induced fluorescence diagnostic for laboratory plasma sources

Cited by 4 publications

References 6 publications

Ion heating in the PISCES-RF liquid-cooled high-power, steady-state, helicon plasma device

Ion heating in the PISCES-RF liquid-cooled high-power, steady-state, helicon plasma device

PISCES-RF: a liquid-cooled high-power steady-state helicon plasma device

Wavelength modulation laser-induced fluorescence for plasma characterization

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