Three-dimensional laser-induced fluorescence measurements in a helicon plasma

Hardin, Robert; Sun, Xuan; Scime, Earl

doi:10.1063/1.1787168

Cited by 13 publications

(8 citation statements)

References 15 publications

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“…13 was capable of measurements at only a single point in space and without temporal information; this diagnostic system is easily extended to utilize our capacity to measure the three-dimensional IVDF via simultaneous repositioning of the injection and collection optics, 10 as well as to perform time-resolved LIF measurements. 17,18 The capability of being able to perform time-resolved IVDFs in two dimensions simultaneously will allow us to investigate the full ion response to waves excited in the plasma.…”

Section: Discussion and Future Plansmentioning

confidence: 99%

“…By changing the direction of the injected beam, without necessarily changing the location of the detector, it is possible to measure the velocity distribution function for two velocity components. 9,10 Some research groups have performed planar LIF measurements in which a laser beam is spread into a sheet and used to illuminate a cross section of a plasma. 11,12 The induced fluorescence is then imaged with a camera, and a two-dimensional image of LIF intensity and flow along the direction of the laser beam was obtained.…”

Section: Introductionmentioning

confidence: 99%

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Simultaneous two-dimensional laser-induced-fluorescence measurements of argon ions

Hansen

Galante

McCarren

et al. 2010

Review of Scientific Instruments

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Recent laser upgrades on the Hot Helicon Experiment at West Virginia University have enabled multiplexed simultaneous measurements of the ion velocity distribution function at a single location, expanding our capabilities in laser-induced fluorescence diagnostics. The laser output is split into two beams, each modulated with an optical chopper and injected perpendicular and parallel to the magnetic field. Light from the crossing point of the beams is transported to a narrow-band photomultiplier tube filtered at the fluorescence wavelength and monitored by two lock-in amplifiers, each referenced to one of the two chopper frequencies.

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Section: Discussion and Future Plansmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Simultaneous two-dimensional laser-induced-fluorescence measurements of argon ions

Hansen

Galante

McCarren

et al. 2010

Review of Scientific Instruments

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“…The different slopes suggest that the helicon wavelength in (1) depends on the magnetic field strength for a fixed driving frequency and fixed antenna length. Although the HELIX LIF system is not absolutely calibrated, we have determined that for argon helicon plasmas, the total LIF signal is roughly proportional to the square of the plasma density times the square root of the electron temperature and can be used as a non-invasive measure of qualitative changes in the plasma density (Hardin et al 2004;Sun et al 2004). See Ref (Sun et al 2004) for an explanation of the atomic physics responsible for this approximate relationship.…”

Section: Experimental Regimes and Key Findingsmentioning

confidence: 99%

The hot hELicon eXperiment (HELIX) and the large experiment on instabilities and anisotropy (LEIA)

et al. 2014

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The West Virginia University Hot hELIcon eXperiment (HELIX) provides variable density and ion temperature plasmas, with controllable levels of thermal anisotropy, for space relevant laboratory experiments in the Large Experiment on Instabilities and Anisotropy (LEIA) as well as fundamental studies of helicon source physics in HELIX. Through auxiliary ion heating, the ion temperature anisotropy (T ⊥ /T || ) is variable from 1 to 20 for parallel plasma beta (β = 8πnkT i /B 2 ) values that span the range of 0.0001 to 0.01 in LEIA. The ion velocity distribution function is measured throughout the discharge volume in steady-state and pulsed plasmas with laser induced fluorescence (LIF). The wavelengths of very short wavelength electrostatic fluctuations are measured with a coherent microwave scattering system. Operating at low neutral pressures triggers spontaneous formation of a current-free electric double layer. Ion acceleration through the double layer is detected through LIF. LIF-based velocity space tomography of the accelerated beam provides a twodimensional mapping of the bulk and beam ion distribution functions. The driving frequency for the m = 1 helical antenna is continuously variable from 8.5 to 16 MHz and frequency dependent variations of the RF coupling to the plasma allow the spontaneously appearing double layers to be turned on and off without modifying the plasma collisionality or magnetic field geometry. Single and multi-species plasmas are created with argon, helium, nitrogen, krypton, and xenon. The noble gas plasmas have steep neutral density gradients, with ionization levels reaching 100% in the core of the plasma source. The large plasma density in the source enables the study of Aflvén waves in the HELIX device. † Email address for correspondence: escime@wvu.edu 2 E. E. Scime et al.

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“…The collection optics used at locations z = 55 cm and z = 115 cm are fixed and collect focused light from the center of the plasma. The collection optics used at z = 85 cm are a part of the two dimensional scanning apparatus described by Hardin et al 15 For measurements at z = 85 cm, the injection optics are also scanned radially to maintain the same collection volume for each radially resolved measurement. Fig.…”

Section: Experimental Apparatusmentioning

confidence: 99%

Measurements of neutral helium density in helicon plasmas

Houshmandyar

Sears

Thakur

et al. 2010

Review of Scientific Instruments

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Laser-induced-fluorescence (LIF) is used to measure the density of helium atoms in a helicon plasma source. For a pump wavelength of 587.725 nm (vacuum) and laser injection along the magnetic field, the LIF signal exhibits a signal decrease at the Doppler shifted central wavelength. The drop in signal results from the finite optical depth of the plasma and the magnitude of the decrease is proportional to the density of excited state neutral atoms. Using Langmuir probe measurements of plasma density and electron temperature and a collisional-radiative model, the absolute ground state neutral density is calculated from the optical depth measurements. Optimal plasma performance, i.e., the largest neutral depletion on the axis of the system, is observed for antenna frequencies of 13.0 and 13.5 MHz and magnetic field strengths of 550-600 G.

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Three-dimensional laser-induced fluorescence measurements in a helicon plasma

Cited by 13 publications

References 15 publications

Simultaneous two-dimensional laser-induced-fluorescence measurements of argon ions

Simultaneous two-dimensional laser-induced-fluorescence measurements of argon ions

The hot hELicon eXperiment (HELIX) and the large experiment on instabilities and anisotropy (LEIA)

Measurements of neutral helium density in helicon plasmas

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