Characteristics of Resonance Probes

Dote, Toshihiko; Ichimiya, T.

doi:10.1063/1.1714368

Cited by 48 publications

(13 citation statements)

References 6 publications

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“…There is a body of early theoretical and experimental work related to the phenomenon of rf resonance both above and below the plasma frequency. [11][12][13] The investigation of collisionless resistance associated with resonance phenomena that is thought to arise due to plasma inhomogeneity, may be said to originate with the work of Tonks. 14 However, the problem did not receive further attention until Herlofson,15 trying to account for resonant scattering observed in connection with ionized meteor trails, was the first to introduce the idea of an effective collision frequency associated with density gradients.…”

Section: Introductionmentioning

confidence: 99%

On collisionless energy absorption in plasmas: Theory and experiment in spherical geometry

et al. 2006

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An investigation of the rf impedance characteristics of a small spherical probe immersed in a laboratory plasma is ongoing in the large Space Physics Simulation Chamber [D. N. Walker et al., Rev. Sci. Instrum. 65, 661 (1994)] at the Naval Research Laboratory. The data taken are from network analyzer measurements of the reflection coefficient obtained when applying a low level rf signal to the probe which is either near floating potential or negatively dc biased in a low pressure plasma. As is well known, sheaths form around objects placed inside plasmas. The electron density is smaller inside the sheath, and the reduction in density alters the plasma impedance. Surprisingly, the impedance becomes “resistive,” even though the plasma is effectively collisionless, at frequencies below the bulk plasma frequency, thus leading to collisionless energy absorption. This behavior comes directly from Maxwell's equations along with the cold fluid equations. The solutions obtained indicate that this form of plasma resistance is inversely proportional to the plasma density gradient evaluated at the location where the plasma frequency is equal to the applied frequency. The sphere for this work is typically near plasma potential or biased more negatively into the ion collection regime. Applying a supplemental, negative dc bias to the sphere thickens the sheath and tends to raise its resistance as the density gradient is softened. Much of the earlier work in the area of collisionless resistance concentrated primarily on planar probes as opposed to the present work which is concerned with spheres. Interpreting the results is simpler for a sphere and the results obtained agree well with theory as described. For comparison to the theory we use only the S11 parameter outputs (or reflection coefficients) of the network analyzer in the experimental series. Significant energy absorption is observed at frequencies generally near one-half the plasma frequency. One result of this work is that the most efficient transfer of power to the plasma occurs not unexpectedly when there is impedance matching between input impedance and output (collisionless) impedance. This paper is an exposition of these ideas along with data results and a comparison to theory for the spherical probe which has not been published in this form.

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Section: Introductionmentioning

confidence: 99%

On collisionless energy absorption in plasmas: Theory and experiment in spherical geometry

et al. 2006

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“…Sheath-plasma resonances first discovered by Takayama, Ikegami, and Miyazaki 3 have been mainly studied for negatively biased electrodes in space 4 ' 5 and in laboratory plasmas. 6,7 In this Letter I present the behavior of the sheath-plasma resonance for a positively biased electrode drawing electron saturation current through an ion-depleted sheath. It is observed that the series resonance vanishes while the parallel antiresonance becomes spontaneously unstable.…”

mentioning

confidence: 99%

Instability of the sheath-plasma resonance

1988

Phys. Rev. Lett.

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An electrode with a positive dc bias inserted into a Maxwellian plasma is observed to generate coherent high-frequency oscillations at the sheath-plasma antiresonance frequency (co^cope). The phenomenon is explained by a negative resistance associated with the finite electron transit time through the sheath. Harmonics of the fundamental are radiated as electromagnetic waves but are clearly shown not to be caused by electron orbital instabilities.PACS numbers: 52.25. Sw, 52.40.Fd, 52.40.Hf, 52.70.GwThe sheath-plasma resonance is a well-known phenomenon in the field of rf probes and antennas in plasmas. 12 Basically, an electron-depleted sheath forms a vacuum capacitor while a field-free cold plasma behaves inductively below the electron plasma frequency (AT = 1 -Q)p/co 2 <0) such that series and parallel resonances are possible. The exact resonance frequency depends on the electrode geometry and sheath thickness and is typically in the range 0.5 < co/co p < 1. Sheath-plasma resonances first discovered by Takayama, Ikegami, and Miyazaki 3 have been mainly studied for negatively biased electrodes in space 4 ' 5 and in laboratory plasmas. 6,7 In this Letter I present the behavior of the sheath-plasma resonance for a positively biased electrode drawing electron saturation current through an ion-depleted sheath. It is observed that the series resonance vanishes while the parallel antiresonance becomes spontaneously unstable. This instability, termed the sheath-plasma instability, is though to arise from a negative differential rf resistance of the current-carrying electron-rich sheath. The finite electron transit time through the sheath 8 (r-co p~x ) leads to a 180° phase shift between rf current and voltage which drives the resonant system unstable, as is known from the theory of diodes with electron inertia. 9

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“…The physical phenomena which RPs exploit have been known since the 1930s [1]. Research performed in the 1960s demonstrated the feasibility of resonance probes and built a theoretical framework for their use [2][3][4][5]. Several different techniques have been developed using resonance probes and have been well characterized [6][7][8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 98%

Evaluation of a Plasma Impedance Probe in a Time-varying Non-uniform Plasma

Hopkins

King

2013

49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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Numerical simulations and experimental measurements were combined to determine the ability of a PIP to measure plasma density and electron collision frequency in a plasma containing spatial gradients as well as time-varying oscillations in the plasma density. Collision frequency was to be measured by the width of the parallel resonance in the real part of plasma impedance-vs.-frequency, while plasma density was to be measured using the zero-crossing of the imaginary impedance-vs.-frequency at parallel resonance. Simulations of the probe characteristic in a plasma gradient indicated that the broadening the real part of plasma impedance due to the spatial gradient obscured the broadening due to electron collision frequency. Simulation results also showed that it may be possible to measure relative changes in electron collision frequencies in a spatial plasma gradient, but the broadening effect of the time-varying oscillations made collision frequency measurements impossible. The time-varying oscillations had the effect of causing multiple zero-crossings in the imaginary part of impedance at parallel resonance. Results of experiments and simulations indicated that the lowest-frequency zero-crossing represented the lowest plasma density in the oscillations and the highest-frequency zero-crossing represented the highest plasma density in the oscillations, thus the PIP probe was found to be an effective tool to measure both the average plasma density as well as the max and min densities due to temporal oscillations. Nomenclature 0 C = vacuum capacitance p C = plasma capacitance sh C = sheath capacitance vac C = vacuum capacitance of the probe 0  = permittivity of free space p  = relative plasma permittivity breathing f = frequency of the breathing mode oscillation Joint Propulsion Conferences noise f = noise in the simulation of electron density oscillations sample f = sampling frequency of the vector network analyzer VNA f = output frequency of the vector network analyzer VNA f  = frequency step in the vector network analyzer sweep e m = electron mass e n = electron number density 0 e n = amplitude of electron density oscillation eAve n = average electron number density n n = neutral density  = electron collision frequency P = pressure  = radius  = collision cross section for xenon e T = electron temperature  = stimulus frequency p  = plasma frequency Z = total probe impedance p Z = plasma impedance sh Z = sheath impedance

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Characteristics of Resonance Probes

Cited by 48 publications

References 6 publications

On collisionless energy absorption in plasmas: Theory and experiment in spherical geometry

On collisionless energy absorption in plasmas: Theory and experiment in spherical geometry

Instability of the sheath-plasma resonance

Evaluation of a Plasma Impedance Probe in a Time-varying Non-uniform Plasma

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