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

Luggenhölscher, Dirk; Çelik, Yusuf; Pu, Yunfei; Czarnetzki, Uwe

doi:10.1088/1742-6596/227/1/012035

Cited by 6 publications

(6 citation statements)

References 10 publications

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“…Therefore, numerous methods are devoted to the experimental and theoretical determination of these distributions [4][5][6][7][8][9][10][11][12][13]. Many of them concentrate on the velocity or energy distributions of electrons (EVDF and EEDF).…”

Section: Introductionmentioning

confidence: 99%

Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

Tsankov

Czarnetzki

2017

Plasma Sources Sci. Technol.

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Non-equilibrium distribution functions of electrons and ions play an important role in plasma physics. A prominent example is the kinetic Bohm criterion. Since its first introduction it has been controversial for theoretical reasons and due to the lack of experimental data, in particular on the ion distribution function. Here we resolve the theoretical as well as the experimental difficulties by an exact solution of the kinetic Boltzmann equation including charge exchange collisions and ionization. This also allows for the first time non-invasive measurement of spatially resolved ion velocity distributions, absolute values of the ion and electron densities, temperatures, and mean energies as well as the electric field and the plasma potential in the entire plasma. The non-invasive access to the spatially resolved distribution functions of electrons and ions is applied to the problem of the kinetic Bohm criterion. Theoretically a so far missing term in the criterion is derived and shown to be of key importance. With the new term the validity of the kinetic criterion at high collisionality and its agreement with the fluid picture are restored. All findings are supported by experimental data, theory and a numerical model with excellent agreement throughout.

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Section: Introductionmentioning

confidence: 99%

Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

Tsankov

Czarnetzki

2017

Plasma Sources Sci. Technol.

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“…[28][29][30] Finally, by using only the bottom coil, the helicon discharge is generated. 33,34 A similar helicon configuration is reported by Stevens et al 35 Time-varying magnetic fields are measured via a bare single induction loop ͑B-dot probe͒. 27 The probe is immersed into the plasma in the upstream and downstream plane for radial measurements.…”

Section: Methodsmentioning

confidence: 84%

Wave propagation and noncollisional heating in neutral loop and helicon discharges

et al. 2011

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Heating mechanisms in two types of magnetized low pressure rf ͑13.56 MHz͒ discharges are investigated: a helicon discharge and a neutral loop discharge. Radial B-dot probe measurements demonstrate that the neutral loop discharge is sustained by helicon waves as well. Axial B-dot probe measurements reveal standing wave and beat patterns depending on the dc magnetic field strength and plasma density. In modes showing a strong wave damping, the plasma refractive index attains values around 100, leading to electron-wave interactions. In strongly damped modes, the radial plasma density profiles are mainly determined by power absorption of the propagating helicon wave, whereas in weakly damped modes, inductive coupling dominates. Furthermore, an azimuthal diamagnetic drift is identified. Measurements of the helicon wave phase demonstrate that initial plane wave fronts are bent during their axial propagation due to the inhomogeneous density profile. A developed analytical standing wave model including Landau damping reproduces very well the damping of the axial helicon wave field. This comparison underlines the theory whereupon Landau damping of electrons traveling along the field lines at speeds close to the helicon phase velocity is the main damping mechanism in both discharges.

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“…As applied power increases, T i⊥ slightly increase while v d⊥ which has almost 0 m/s is not significant changes as shwon in figure 7(a). This result with the fixed gas flow rate at 80 sccm indicates low dependence on an applied power, because measurement position is very close to the center axis [27,29] and the the energy losses of argon ions by frequent collisions are still stronger than energy transfers from electrons to argon ions in spite of generating higher electric potential at 1 kW. For the case of lower gas flow rate at 20 sccm as shown in figure 7(b), T i⊥ and v d⊥ considerably increase by comparison with 80 sccm, which indicates that less collisions with low flow rate is enough to increase the temeprature and velocity of argon ions.…”

Section: Resultsmentioning

confidence: 99%

Development of a Laser Induced Fluorescence (LIF) system on the Plasma Material Interaction System (PLAMIS-II) device

Kang

Lee

et al. 2015

J. Inst.

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

Cited by 6 publications

References 10 publications

Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

Wave propagation and noncollisional heating in neutral loop and helicon discharges

Development of a Laser Induced Fluorescence (LIF) system on the Plasma Material Interaction System (PLAMIS-II) device

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