Observations of neutral depletion and plasma acceleration in a flowing high-power argon helicon plasma

Denning, C.M.; Wiebold, Matt; Scharer, J.E.

doi:10.1063/1.2950301

Cited by 42 publications

(32 citation statements)

References 29 publications

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“…Previous research on the Madison Helicon eXperiment (MadHeX) experiment has explored neutral depletion 28 and bulk plasma acceleration (to $1 km=s) at high rf powers (500 W-3 kW) and high ionization levels (96%) at higher gas pressures (1-10 mTorr Ar) and flow rates (18-150 sccm) in a nozzle magnetic field. Tysk 29 utilized this facility without the expansion chamber with a uniform magnetic field at higher pressures (3 mTorr) and powers (800 W) to investigate the variation of radial density and electron temperature profiles with magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Experimental observation of ion beams in the Madison Helicon eXperiment

2011

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Argon ion beams up to E b ¼ 165 eV at P rf ¼ 500 W are observed in the Madison Helicon eXperiment (MadHeX) helicon source with a magnetic nozzle. A two-grid retarding potential analyzer (RPA) is used to measure the ion energy distribution, and emissive and rf-filtered Langmuir probes measure the plasma potential, electron density, and temperature. The supersonic ion beam (M ¼ v i =c s up to 5) forms over tens of Debye lengths and extends spatially for a few ion-neutral charge-exchange mean free paths. The parametric variation of the ion beam energy is explored, including flow rate, rf power, and magnetic field dependence. The beam energy is equal to the difference in plasma potentials in the Pyrex chamber and the grounded expansion chamber. The plasma potential in the expansion chamber remains near the predicted eV p $ 5kT e for argon, but the upstream potential is much higher, likely due to wall charging, resulting in accelerated ion beam energies E b ¼ e[V beam À V plasma ] > 10kT e .

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Section: Introductionmentioning

confidence: 99%

Experimental observation of ion beams in the Madison Helicon eXperiment

2011

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“…A variation over the discharge volume of the gas pressure when the discharge is in a flowing gas is in agreement with both theoretical and experimental results 17,18,38 obtained, moreover, in a source with a configuration close to that considered here (the BATMAN source 23 ). Strong contribution of the electron pressure to the total pressure has also been observed 39,40 at high RF power in lowpressure discharges of different type and in different gases. FIG.…”

Section: B Neutral Particle Behaviormentioning

confidence: 78%

Low-pressure hydrogen discharge maintenance in a large-size plasma source with localized high radio-frequency power deposition

et al. 2015

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Articles you may be interested inDevelopment of a low-energy and high-current pulsed neutral beam injector with a washer-gun plasma source for high-beta plasma experiments Rev. Sci. Instrum. 83, 083504 (2012); 10.1063/1.4744960 Modeling a high power fusion plasma reactor-type ion source: Applicability of particle methods Phys. Plasmas 19, 043506 (2012); 10.1063/1.3696037 Cesium dynamics in long pulse operation of negative hydrogen ion sources for fusiona) Rev. Sci. Instrum. 83, 02B110 (2012); 10.1063/1.3670347 Simulation of cesium injection and distribution in rf-driven ion sources for negative hydrogen ion generationa) Rev. Sci. Instrum. 81, 02A706 (2010);The development of the two-dimensional fluid-plasma model of a low-pressure hydrogen discharge, presented in the study, is regarding description of the plasma maintenance in a discharge vessel with the configuration of the SPIDER source. The SPIDER source, planned for the neutralbeam-injection plasma-heating system of ITER, is with localized high RF power deposition to its eight drivers (cylindrical-coil inductive discharges) and a large-area second chamber, common for all the drivers. The continuity equations for the charged particles (electrons and the three types of positive ions) and for the neutral species (atoms and molecules), their momentum equations, the energy balance equations for electrons, atoms and molecules and the Poisson equations are involved in the discharge description. In addition to the local processes in the plasma volume, the surface processes of particle reflection and conversion on the walls as well as for a heat exchange with the walls are included in the model. The analysis of the results stresses on the role of the fluxes (particle and energy fluxes) in the formation of the discharge structure. The conclusion is that the discharge behavior is completely obeyed to non-locality. The latter is displayed by: (i) maximum values of plasma parameters (charged particle densities and temperatures of the neutral species) outside the region of the RF power deposition, (ii) shifted maxima of the electron density and temperature, of the plasma potential and of the electron production, (iii) an electron flux, with a vortex structure, strongly exceeding the total ion flux which gives evidence of a discharge regime of nonambipolarity and (iv) a spatial distribution of the densities of the neutral species resulting from their fluxes. [http://dx.

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“…Awell-known phenomenon that affects helicon source operation is "neutral pumping," (i.e., the depletion of neutral particles from the core region of the source), which leads to limitations in the attainable plasma density and ionization efficiency [4,12,29,[31][32][33][34][35][36]. Reductions in neutral particle density of one order of magnitude or more have been observed in the core of helicon discharges [4,12,36], both with respect to the cold flow values and between different regions in the source.…”

Section: Effect Of Neutral Particle Density On Helicon Source Opementioning

confidence: 99%

“…Reductions in neutral particle density of one order of magnitude or more have been observed in the core of helicon discharges [4,12,36], both with respect to the cold flow values and between different regions in the source. Neutral pumping accounts for the emergence of different helicon modes [32], for nonmonotonic variation of plasma density with varying RF power [34], for electron species heating by limitation of RF power deposition into ionization [35], for the radial nonhomogeneity of plasma properties [33], and for the inception of discharge oscillations in connection to neutral particle ingestion in vacuum chambers [31]. Several mechanisms are thought to be behind the neutral pumping phenomenon: heating of neutral particle [4], which requires lower neutral density to preserve pressure balance in the source; neutral particle diffusion [12]; and "ion pumping," that is, the diffusion of ionized atoms to the wall of the tube being much faster (because of presheath electric fields) than the diffusion of neutral atoms (generated by recombination) from the wall to the core of the plasma [33].…”

Section: Effect Of Neutral Particle Density On Helicon Source Opementioning

confidence: 99%

Neutral Gas Expansion in a Cylindrical Helicon Discharge Chamber

Giannelli

Kieckhafer

Walker

2013

Journal of Propulsion and Power

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The expansion of neutral gas in an open-ended cylindrical chamber into a large vacuum facility is investigated to understand neutral particle density distribution. The cylindrical chamber geometry with a single on-axis gas injection port is representative of a helicon plasma source discharge chamber. The neutral gas pressure profile along the cylinder wall is experimentally measured for argon and xenon mass flow rates of 0-200 sccm, at facility pressures up to 3 × 10 −5 and 3.8 × 10 −5 torr Ar and torr Xe, respectively. The average relative error between the experimentally measured pressure profiles and the numerical results obtained with a direct simulation Monte Carlo code is less than 10%, with the maximum relative error below 30%. The single on-axis injection port into the cylindrical discharge chamber results in a nonuniform neutral particle density distribution in the source due to the recirculation zone generated in the rear of the discharge chamber. This highlights the potential impact of the propellant injection system design on the neutral particle depletion phenomenon in helicon plasma sources.

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Observations of neutral depletion and plasma acceleration in a flowing high-power argon helicon plasma

Abstract: Articles you may be interested inLow-pressure, high-density, and supersonic plasma flow generated by a helicon magnetoplasmadynamic thruster Appl.

Cited by 42 publications

References 29 publications

Experimental observation of ion beams in the Madison Helicon eXperiment

Experimental observation of ion beams in the Madison Helicon eXperiment

Low-pressure hydrogen discharge maintenance in a large-size plasma source with localized high radio-frequency power deposition

Neutral Gas Expansion in a Cylindrical Helicon Discharge Chamber

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