Helicon modes in a cylindrical plasma source

A high density 'blue' mode has been observed when operating the Helicon Double Layer Thruster (HDLT) with xenon. Using a Langmuir probe and a retarding field energy analyser (RFEA), the plasma source and exhaust have been characterized at various radio frequency (RF) powers and operating pressures. When operating at low RF powers, the HDLT prototype is shown to be in a capacitively coupled mode. As the RF power is increased, a discrete mode transition occurs over a small RF power range (at about 625 W at 0.45 mTorr) and the plasma inside the source increases in density significantly and changes to a bright white/blue colour. This high density mode exhibits hysteresis, and radial measurements inside the source reveal a centrally peaked profile that is indicative of a helicon wave-sustained discharge. The quality, or Q, factor of the matching box is determined as a function of RF power and is shown to decrease in the high density mode, consistent with the increase in plasma density observed. The xenon exhaust of the HDLT prototype is investigated axially with the Langmuir probe and the RFEA and is shown to follow a Boltzmann expansion with an electron temperature of about 6 eV.

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“…In inductively coupled systems, the plasma density increases linearly with increasing input power [14], such that n ∝ P RF .…”

Section: Operating Modes In Rf Dischargesmentioning

confidence: 99%

High density mode in xenon produced by a Helicon Double Layer Thruster

West¹,

Charles²,

Boswell³

2009

J. Phys. D: Appl. Phys.

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“…This turns out to be a serious obstacle for the development of automatic control systems for plasma processing applications. 2 Mode jumps have recently become a subject of increasing concern for inductively coupled ͑IC͒, [3][4][5][6][7] helicon-wave sustained, 2,8,9 electron cyclotron resonance, 10 and microwave slot-excited ͑MSE͒ ͑Refs. 11-13͒ plasmas.…”

Section: Introductionmentioning

confidence: 99%

Power transfer and mode transitions in low-frequency inductively coupled plasmas

Ostrikov

2000

Journal of Applied Physics

100

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Operation and mode jumps in low-frequency (500 kHz) radio-frequency inductively coupled plasmas are investigated. The discharge is driven by a flat inductive coil which can excite the electrostatic (E) and electromagnetic (H) discharge modes. The power transfer efficiency and mode transition behavior are studied. It is found that the power reflection coefficient as a function of the input power is minimal in the vicinity of the mode transitions and exhibits hysteresis, which is also observed when the operating gas pressure is varied.

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“…The appearance of the core is typically used as an identification of the helicon mode [4], [13], [17], [20], [22]. The formation of a bright core is not restricted to argon helicon plasma, but has been observed for other working gases such as xenon [23] and krypton [24].…”

mentioning

confidence: 99%

Formation of the Blue Core in Argon Helicon Plasma

Thakur

Brandt

Cui

et al. 2015

IEEE Trans. Plasma Sci.

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Helicon plasmas are typically associated with a core, a radially localized central area of strong ion light emission. Here, we investigate the role of electrostatic instabilities that lead to the formation of the classic blue core. We show that helicon plasma can also occur without the distinct core. In these conditions, the plasma is dominated by low-frequency resistive drift wave (RDW) instabilities propagating in the electron diamagnetic drift direction. When the intense sharp core is present, a new global equilibrium state is achieved where three radially separated plasma instabilities exist simultaneously. The density gradient driven RDWs separate the plasma radially into an edge region and a core region. The edge is dominated by strong, turbulent, shear-driven instabilities, while the core shows very coherent high azimuthal mode number fluctuations propagating in the ion diamagnetic drift direction and associated with enhanced ion emission. The particle flux is directed outward for small radii and inward for large radii, thus forming a radial particle transport barrier. The radial extent of the inner mode and radial location of the particle transport barrier is the same as the radius of the blue core. This new equilibrium, with the three coexisting radially separated plasma instabilities, leads to the formation of a very strong enhanced blue core. For a range of operating parameters, just prior to the blue core formation, the system undergoes incomplete intermittent transitions between the two equilibrium states, leading to the visual perception of a broad less intense helicon core. This is the first time that the development of the helicon core is shown to be associated with changes in radial transport driven by inherent low-frequency plasma instabilities.

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Helicon modes in a cylindrical plasma source

Cited by 37 publications

References 10 publications

High density mode in xenon produced by a Helicon Double Layer Thruster

High density mode in xenon produced by a Helicon Double Layer Thruster

Power transfer and mode transitions in low-frequency inductively coupled plasmas

Formation of the Blue Core in Argon Helicon Plasma

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