Measurement of Plasma Presheath

Meassick, S.; Cho, M. H.; Hershkowitz, N.

doi:10.1109/tps.1985.4316372

Cited by 39 publications

(12 citation statements)

References 12 publications

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“…Divertors and limiters in fusion plasma devices, substrates in etching and deposition plasmas, and Langmuir probes are among the many examples where the plasma-wall interaction is a prominent feature of the system and in which multiple ion species are often present. Understanding sheath formation in such plasmas, a longstanding problem [1 -3], remains a practical problem of critical interest in plasma science [4][5][6][7]. Its recent revival among plasma theorists in both the DC and RF communities [8][9][10][11][12][13] has begun to be matched by relevant experiments, however it is still true that theory is ahead of experiment.…”

Section: Introductionmentioning

confidence: 99%

Ion flow and sheath physics studies in multiple ion species plasmas using diode laser based laser-induced fluorescence

Severn

Wang

et al. 2006

Thin Solid Films

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Diode lasers have proved to be a valuable light source for laser-induced fluorescence (LIF) measurements for plasma science since the early 1990s, and they have recently improved the state of the art of measuring ion flow from ion velocity distribution functions (ivdfs) at the sheath -presheath boundary in single and multiple ion species plasmas. In the case of a low temperature two ion species plasma (ArI + HeI), we were the first to show experimentally that ion species may reach the sheath edge flowing at a very different speed than that expected from the single species Bohm Criterion (ArII ions exceed the individual Bohm flow speed by almost a factor of 2 at the sheath edge). Simulation results are found to agree. Diode laser technology relevant to LIF measurements in multiple ion species plasmas is discussed with the aim of addressing outstanding problems in sheath formation in such plasmas. D

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Section: Introductionmentioning

confidence: 99%

Ion flow and sheath physics studies in multiple ion species plasmas using diode laser based laser-induced fluorescence

Severn

Wang

et al. 2006

Thin Solid Films

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“…Presheaths have been recognized since 1949 [12] and are thought to correspond to a variety of mechanisms. For example, in unmagnetized ''collisionless'' plasmas, they are associated with the plasma production mechanism and can be as large as half the size (L=2) of the confinement device [13]. In weakly collisional plasmas, if the ion-neutral collision length L=2, the presheath length is found to be ' [14].…”

mentioning

confidence: 99%

First Experimental Measurements of the Plasma Potential throughout the Presheath and Sheath at a Boundary in a Weakly Collisional Plasma

2002

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Experimental data obtained with emissive probes and Langmuir probes show that the plasma potential profile in the presheath scales as -ephi /T(e)= sqrt[(x(0) -x)/lambda ], consistent with ion flux conservation, and that the sheath consists of a transition region and an electron-free collisionless sheath with thicknesses scaling as lambda( 1/5)lambda (4/5 )(D) and lambda(D )(ephi/ T(e))(3 /4), respectively, where lambda is the ion-neutral collision length. Results support Rieman's presheath and transitional region model [Phys. Plasmas 4, 4158 (1997)]]. The potential drop over the presheath and transition sheath region were the order of T(e) /e and 2T(e )/3e, respectively, increasing with increasing pressure.

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“…This technique has previously been used for experimental studies of the potential profiles in sheaths 27,28 and presheaths. [29][30][31] Dust grains levitated in the plasma sheath are monodisperse polystyrene divinylbenzene beads 10.0Ϯ0.5 m in diameter, a density of 1.05ϫ10 3 kg/m 3 , and a mass of 5.5 ϫ10 Ϫ13 kg, which gives a gravitational force of F g ϭ5.6 ϫ10 Ϫ12 N. These grains are sufficiently large to be easily seen in the video images. Grains can be raised into the sheath by striking the plate using an insulated hammer on a vacuum feedthrough but this is not necessary at plate biases more negative than approximately Ϫ27 V. An argon laser illuminates the grains and a charge-coupled device ͑CCD͒ camera viewing through a laser line filter ͑488Ϯ2 nm͒ records positions.…”

Section: A Apparatusmentioning

confidence: 99%

Dust grain charging and levitation in a weakly collisional sheath

et al. 2003

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An experiment is described in which monodisperse dust grains are levitated within a dc sheath above a conducting plate in argon plasma. For plate bias voltages that are not too negative ͑уϪ10 electron temperatures͒, the observed dust levitation heights are near to values calculated from a model combining equations for the sheath with those for grain charging. When the plate is more negatively biased, the theoretical levitation heights are higher than the observed heights as a consequence of the measured sheath thickness being smaller than values obtained from the models.

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Measurement of Plasma Presheath

Cited by 39 publications

References 12 publications

Ion flow and sheath physics studies in multiple ion species plasmas using diode laser based laser-induced fluorescence

Ion flow and sheath physics studies in multiple ion species plasmas using diode laser based laser-induced fluorescence

First Experimental Measurements of the Plasma Potential throughout the Presheath and Sheath at a Boundary in a Weakly Collisional Plasma

Dust grain charging and levitation in a weakly collisional sheath

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