Evolution of the parallel and perpendicular ion velocity distribution functions in pulsed helicon plasma sources obtained by time resolved laser induced fluorescence

Biloiu, Costel; Sun, Xuan; Choueiri, Edgar Y.; Doss, F. W.; Scime, Earl; Heard, J. W.; Spektor, Rostislav; Ventura, D.

doi:10.1088/0963-0252/14/4/016

Cited by 41 publications

(33 citation statements)

References 68 publications

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“…These features are very similar to the work presented in references [2,[6][7][8][9][10][11][12][13][14][15][16]. The most significant difference from the above references is the spatial variation of the ion beam flux in the downstream region.…”

Section: A Existence Of a Double Layer And Spatial Dependenciessupporting

confidence: 85%

“…[13]. The DL position also depends on the geometry of the reactor, but remains close to the source -diffusion chamber junction (slightly downstream in WOMBAT [11], and slightly upstream in Chi-Kung [2], HELIX [15] and our source). These experiments show that above the critical magnetic field at which the DL forms, the DL characteristics do not depend on the magnetic field magnitude; thus the topology of the magnetic field might be the key parameter.…”

Section: B Magnetic Field and Pressure Dependencementioning

confidence: 92%

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Experimental investigation of double layers in expanding plasmas

2007

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Double layers (DLs) have been observed in a plasma reactor composed of a source chamber attached to a larger expanding chamber. Positive ion beams generated across the DL were characterized in the low plasma potential region using retarding field energy analyzers. In electropositive gases, DLs were formed at very low pressures (between 0.1 and 1 mTorr) with the plasma expansion forced by a strongly diverging magnetic field. The DL remains static, robust to changes in boundary conditions, and its position is related to the magnetic field lines. The voltage drop across the DL increases with decreasing pressure, i.e. with increasing electron temperature (around 20 V at 0.17 mTorr). DLs were also observed in electronegative gases without a magnetic field over a greater range of pressure (0.5 to 10 mTorr). The actual profile of the electronegative DL is very sensitive to external parameters and intrusive elements, and they propagate at high negative ion fraction. Electrostatic probes measurements and laser induced photodetachment show discontinuities in all plasma parameters (electron density, electron temperature, negative ion fraction) at the DL position. The voltage drop across the electronegative DL is about 8 V, is independent of the gas pressure and therefore of the electron temperature.

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Section: A Existence Of a Double Layer And Spatial Dependenciessupporting

confidence: 85%

Section: B Magnetic Field and Pressure Dependencementioning

confidence: 92%

Experimental investigation of double layers in expanding plasmas

2007

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“…Here measurements of the argon ion velocity are performed in order to obtain the velocity profiles radially and axially resolved. Similar measurements have been performed before [5,6] but not yet in this kind of flat coil helicon discharge.…”

Section: Introductionsupporting

confidence: 72%

Argon ion velocity distributions in a helicon discharge measured by laser induced fluorescence

Luggenhölscher

Çelik

et al. 2010

J. Phys.: Conf. Ser.

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Argon ion velocity distributions in a helicon discharge measured by laser induced fluorescence Abstract. A Helicon discharge in argon at low gas pressure of 0.1 Pa is generated with a flat coil antenna operated with 13.56 MHz. The power coupled into the discharge is around 1 kW which leads to an electron density of 10 12 cm -3 . The velocity and temperature of the argon ions is measured by laser induced fluorescence (LIF) spatially resolved in radial and axial direction. Ambipolar diffusion accelerates the ions out of the heating region of the discharge with velocities up to 800 m/s. Due to homogenisation of the kinetic energy, the ion temperature increases from 0.15 eV in the centre to 0.4 eV at the edge of the plasma volume.

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“…The strength of the current-carrying DL grows in response to the increasing preferential loss of ion flux (from n i [t] growing in the MC) until steady-state flow is achieved. These early-time processes occur on too short a time scale, and with too small fields and densities, to be temporally and accurately resolved with MNX measurements at this time, but some were seen in experiments of higher density expanding plasma [23][24][25][26].…”

Section: Discussion Of Double Layer Formationmentioning

confidence: 93%

Particle-in-cell modeling of magnetized argon plasma flow through small mechanical apertures

Sefkow

Cohen

2009

Physics of Plasmas

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Motivated by observations of supersonic argon-ion flow generated by linear helicon-heated plasma devices, a three-dimensional particle-in-cell (PIC) code is used to study whether stationary electrostatic layers form near mechanical apertures intersecting the flow of magnetized plasma. By self-consistently evaluating the temporal evolution of the plasma in the vicinity of the aperture, the PIC simulations characterize the roles of the imposed aperture and applied magnetic field on ion acceleration. The PIC model includes ionization of a background neutral-argon population by thermal and superthermal electrons, the latter found upstream of the aperture. Near the aperture, a transition from a collisional to a collisionless regime occurs. Perturbations of density and potential, with mm wavelengths and consistent with ion acoustic waves, propagate axially. An ion acceleration region of length ∼ 200 − 300 λD,e forms at the location of the aperture and is found to be an electrostatic double layer, with axially-separated regions of net positive and negative charge. Reducing the aperture diameter or increasing its length increases the double layer strength.

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Evolution of the parallel and perpendicular ion velocity distribution functions in pulsed helicon plasma sources obtained by time resolved laser induced fluorescence

Cited by 41 publications

References 68 publications

Experimental investigation of double layers in expanding plasmas

Experimental investigation of double layers in expanding plasmas

Argon ion velocity distributions in a helicon discharge measured by laser induced fluorescence

Particle-in-cell modeling of magnetized argon plasma flow through small mechanical apertures

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