Recovery of a weakly magnetized negative-ion plasma after photodetachment

Ivanov, A. A.; Sionov, A. B.; Balghiti-Sube, F. El; Bacal, M.

doi:10.1103/physreve.55.956

Cited by 16 publications

(15 citation statements)

References 13 publications

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“…8 We will show in the present article that the experimentally determined ratio I − / I e in typical volume sources with the magnetic filter extending to the plasma electrode is three to four orders of magnitude higher than the mentioned value. This leads, with T − = 0.2T e to I − / I e = 0.001.…”

Section: Introductionmentioning

confidence: 57%

Extraction physics in volume H−-ion sources

Bacal

Hatayama

Matsumiya

et al. 2006

Review of Scientific Instruments

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Effect of non-uniform electron energy distribution function on plasma production in large arc driven negative ion sourcea) Rev. Sci. Instrum. 83, 02A719 (2012); 10.1063/1.3673485Simulation of cesium injection and distribution in rf-driven ion sources for negative hydrogen ion generationa) Rev. Sci. Instrum. 81, 02A706 (2010);Recent hydrogen negative-ion sources ͑JT60, large helical device ͑LHD͒͒ operate with a magnetic filter field extending up to the plasma electrode and extraction opening. As shown earlier such a magnetic field has a strong effect upon the value of the extracted negative ion and electron current. Measurements of the negative ion and electron density were performed in the ion source, both in the magnetic-field-free region and in the region near the plasma electrode. This work presents the experimental value of the ratio between the extracted negative ion and electron current in different sources. It is shown that the measured current ratio is considerably higher than what can be predicted from a simple thermal flux model based on the density ratio in the bulk of the plasma. We also calculated the ratio between the extracted negative ion and electron currents based on the measured ratio between the negative ion and electron density near the extraction opening using the different theoretical models for electron flux: ͑1͒ thermal flux model ͑I − / I e ͒ thermal and ͑2͒ collisional flux model ͑I − / I e ͒ coll . The comparisons show that ͑I − / I e ͒ thermal is considerably smaller, while ͑I − / I e ͒ coll tends to be larger than the experimental value. The underlying physics of this discrepancy is discussed.

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Section: Introductionmentioning

confidence: 57%

Extraction physics in volume H−-ion sources

Bacal

Hatayama

Matsumiya

et al. 2006

Review of Scientific Instruments

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“…In order to "climb out" this barrier (∼k B T e if there were only electrons and positive ions) they should have enough energy, unless PG is biased at a potential close to the plasma potential. In fact, photodetachment measurements [47] effected near the PG of the source Camambert III showed that the H -gain a directed velocity towards the grid varying from 0.5 c s (very close to thermal velocity) at Φ PG =0 V up to 0.95 c s at Φ PG =4 V (the plasma potential in that experiment is lying between 2 to 3 V).…”

Section: Plasma Grid Bias Effectmentioning

confidence: 81%

Modeling of a negative ion source. II. Plasma-gas coupling in the extraction region

et al. 2008

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“…In nonmagnetized or weakly magnetized plasmas the decay rate corresponds to the refilling time of negative ions from the adjacent layer which is governed by the negative ion temperature. 25,26 However, at a probe position of 10 cm, the magnetic field is strong enough ͑B ϳ 0.005 T͒ over the probe length ͑as it cuts radial flux͒ to reduce the cross-field transport of electrons as they try to diffuse outward to regions of unperturbed plasma. Therefore, the photodetached region of the plasma along the beam remains electropositive over a greater time period.…”

Section: Resultsmentioning

confidence: 99%

Resonance hairpin and Langmuir probe-assisted laser photodetachment measurements of the negative ion density in a pulsed dc magnetron discharge

Bradley¹,

Dodd²,

You³

et al. 2011

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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The time-resolved negative oxygen ion density n− close to the center line in a reactive pulsed dc magnetron discharge (10 kHz and 50% duty cycle) has been determined for the first time using a combination of laser photodetachment and resonance hairpin probing. The discharge was operated at a power of 50 W in 70% argon and 30% oxygen gas mixtures at 1.3 Pa pressure. The results show that the O− density remains pretty constant during the driven phase of the discharge at values typically below 5×1014 m−3; however, in the off-time, the O− density grows reaching values several times those in the on-time. This leads to the negative ion fraction (or degree of electronegativity) α=n−/ne being higher in the off phase (maximum value α∼1) than in the on phase (α=0.05–0.3). The authors also see higher values of α at positions close to the magnetic null than in the more magnetized region of the plasma. This fractional increase in negative ion density during the off-phase is attributed to the enhanced dissociative electron attachment of highly excited oxygen molecules in the cooling plasma. The results show that close to the magnetic null the photodetached electron density decays quickly after the laser pulse, followed by a slow decay over a few microseconds governed by the negative ion temperature. However, in the magnetized regions of the plasma, this decay is more gradual. This is attributed to the different cross-field transport rates for electrons in these two regions. The resonance hairpin probe measurements of the photoelectron densities are compared directly to photoelectron currents obtained using a conventional Langmuir probe. There is good agreement in the general trends, particularly in the off-time.

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Recovery of a weakly magnetized negative-ion plasma after photodetachment

Cited by 16 publications

References 13 publications

Extraction physics in volume H−-ion sources

Extraction physics in volume H−-ion sources

Modeling of a negative ion source. II. Plasma-gas coupling in the extraction region

Resonance hairpin and Langmuir probe-assisted laser photodetachment measurements of the negative ion density in a pulsed dc magnetron discharge

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