Saturation of the magnetic confinement in weakly ionized plasma

Lucken, Romain; Tavant, Antoine; Bourdon, Anne; Lieberman, M. A.; Chabert, Pascal

doi:10.1088/1361-6595/ab38b2

Cited by 9 publications

(15 citation statements)

References 30 publications

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“…For instance, Sternberg and Godyak analyzed the changes in density gradient of magnetized plasmas in cylindrical coordinates through an analytic approach based on magnetic and collision parameters [17]. Lucken et al pointed out that previous studies did not consider plasma instability and emphasized the importance of the plasma confinement parameter, or edge-to-center density ratio (h-factor), which reflects the change in collisonality due to instability [18]. The theoretical works can reasonably explain the anomalous diffusion rate found in the experimental works; however, no experimental study so far has precisely measured the plasma properties along with identifying instability.…”

Section: Introductionmentioning

confidence: 99%

Magnetic confinement and instability in partially magnetized plasma

Kim

Jang

Choi

et al. 2021

Plasma Sources Sci. Technol.

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Discharge with an external magnetic field is promising for various applications of low-temperature plasmas from electric propulsion to semiconductor processes owing to high plasma density. It is essential to understand plasma transport across the magnetic field because plasma confinement under the field is based on strong magnetization of light electrons, maintaining quasi-neutrality through the inertial response of unmagnetized ions. In such a partially magnetized plasma, different degrees of magnetization between electrons and ions can create instability and make the confinement and transport mechanisms more complex. Theoretical studies have suggested a link between the instability of various frequency ranges and plasma confinement, whereas experimental work has not been done so far. Here, we experimentally study the magnetic confinement properties of a partially magnetized plasma considering instability. The plasma properties show non-uniform characteristics as the magnetic field increases, indicating enhanced magnetic confinement. However, the strengthened electric field at the edge of the plasma column gives rise to the Simon–Hoh instability, limiting the plasma confinement. The variation of the edge-to-center plasma density ratio (h-factor) with the magnetic field clearly reveals the transition of the transport regime through triggering of the instability. Eventually, the h-factor reaches an asymptotic value, indicating saturation of magnetic confinement.

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Section: Introductionmentioning

confidence: 99%

Magnetic confinement and instability in partially magnetized plasma

Kim

Jang

Choi

et al. 2021

Plasma Sources Sci. Technol.

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“…The second assumption reflects that symmetry breaking plasma instabilities are generally not significant for the rather weak magnetic fields (B ≤ 10 mT) considered in this study [58][59][60].…”

Section: The Device Under Study and Its Operation Regimementioning

confidence: 98%

“…32 which displays a phase-resolved map of the radially weighted electron power input rP e = rj er E r . Its individual constituents, defined on the basis of the electrical field analysis (59), are displayed in Fig. 34:…”

Section: Case With Magnetic Fieldmentioning

confidence: 99%

Electron dynamics in planar radio frequency magnetron plasmas: I. The mechanism of Hall heating and the μ-mode

Eremin¹,

Engel²,

Krüger³

et al. 2022

Preprint

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The electron dynamics and the mechanisms of power absorption in radio-frequency (RF) driven, magnetically enhanced capacitively coupled plasmas (MECCPs) at low pressure are investigated.The device in focus is a geometrically asymmetric cylindrical magnetron with a radially nonuniform magnetic field in axial direction and an electric field in radial direction. The dynamics is studied analytically using the cold plasma model and a single-particle formalism, and numerically with the inhouse energy and charge conserving particle-in-cell/Monte Carlo collisions code ECCOPIC1S-M.It is found that the dynamics differs significantly from that of an unmagnetized reference discharge.In the magnetized region in front of the powered electrode, an enhanced electric field arises during sheath expansion and a reversed electric field during sheath collapse. Both fields are needed to ensure discharge sustaining electron transport against the confining effect of the magnetic field.The corresponding azimuthal E×B-drift can accelerate electrons into the inelastic energy range which gives rise to a new mechanism of RF power dissipation. It is related to the Hall current and is different in nature from Ohmic heating, as which it has been classified in previous literature.The new heating is expected to be dominant in many magnetized capacitively coupled discharges.It is proposed to term it the "µ-mode" to separate it from other heating modes.

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“…Due to the enhanced power absorption and ionization efficiency in magnetized capacitively coupled radio-frequency (CCRF) discharges compared to their DC counterparts, the magnetic fields that are normally used in rfMS are relatively weak (< 20 mT). Therefore, here we will assume that the electron transport perpendicular to the magnetic field lines is dominated by classical mechanisms -the collision and polarization (inertial) drifts [1] , since instabilities causing the anomalous transport typically emerge for larger magnetic fields [16,17,18,19]. The anticipated absence of such instabilities allows us to adopt the azimuthal symmetry and resolve only the radial and axial coordinates.…”

Section: Introductionmentioning

confidence: 99%

Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code

Eremin¹,

Berger²,

Engel³

et al. 2022

Preprint

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The present work investigates electron transport and heating mechanisms using an (r, z) particle-in-cell (PIC) simulation of a typical rf-driven axisymmetric magnetron discharge with a conducting target. Due to a strong geometric asymmetry and a blocking capacitor, the discharge features a large negative self-bias conducive to sputtering applications. Employing decomposition of the electron transport parallel and perpendicular to the magnetic field lines, it is shown that for the considered magnetic field topology the electron current flows through different channels in the (r, z) plane: a "transverse" one, which involves current flow through the electrons' magnetic confinement region (EMCR) above the racetrack, and two "longitudinal" ones, where electrons' guiding centers move along the magnetic field lines. Electrons gain energy from the electric field along these channels following various mechanisms, which are rather distinct from those sustaining dc-powered magnetrons. The longitudinal power absorption involves mirror-effect heating (MEH), nonlinear electron resonance heating (NERH), magnetized bounce heating (MBH), and the heating by the ambipolar field at the sheath-presheath interface. The MEH and MBH represent two new mechanisms missing from the previous literature. The MEH is caused by a reversed electric field needed to overcome the mirror force generated in a nonuniform magnetic field to ensure sufficient flux of electrons to the powered electrode, and the MBH is related to a possibility for an electron to undergo multiple reflections from the expanding sheath in the longitudinal channels connected by the arc-like magnetic field. The electron heating in the transverse channel is caused mostly by the essentially collisionless Hall heating in the EMCR above the racetrack, generating a strong E × B azimuthal drift velocity. The latter mechanism results in an efficient electron energization, i.e., energy transfer from the electric field to electrons in the inelastic range. Since the main electron population energized by this mechanism remains

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Saturation of the magnetic confinement in weakly ionized plasma

Cited by 9 publications

References 30 publications

Magnetic confinement and instability in partially magnetized plasma

Magnetic confinement and instability in partially magnetized plasma

Electron dynamics in planar radio frequency magnetron plasmas: I. The mechanism of Hall heating and the μ-mode

Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code

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