Effect of space-charge limited emission on measurements of plasma potential using emissive probes

Ye, M. Y.; Takamura, S.

doi:10.1063/1.874210

Cited by 116 publications

(139 citation statements)

References 10 publications

(10 reference statements)

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“…We used a filament current of 2.9 A. This method is expected to give a potential slightly lower than the plasma potential with an accuracy of the order of T e /e [35,36]. Figure 3A shows an example of a logarithmic plot of collector current vs. discriminator voltage from the electron-RFEA in Njord at r = −7 cm.…”

Section: Methodsmentioning

confidence: 99%

RFEA Measurements of High-Energy Electrons in a Helicon Plasma Device with Expanding Magnetic Field

Gulbrandsen

Fredriksen

2017

Front. Phys.

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In the inductively coupled plasma of the Njord helicon device we have, for the same parameters as for which an ion beam exists, measured a downstream population of high-energy electrons emerging from the source. Separated measurements of energetic tail electrons was carried out by Retarding Field Energy Analyzer (RFEA) with a grounded entrance grid, operated in an electron collection mode. In a radial scan with the RFEA pointed toward the source, we found a significant population of high-energy electrons just inside the magnetic field line mapping to the edge of the source. A second peak in high-energy electrons density was observed in a radial position corresponding to the radius of the source. Also, throughout the main column a small contribution of high-energy electrons was observed. In a radial scan with a RFEA biased to collect ions a localized increase in the plasma ion density near the magnetic field line emerging from the plasma near the wall of the source was observed. This is interpreted as a signature of high-energy electrons ionizing the neutral gas. Also, a dip in the floating potential of a Langmuir probe is evident in this region where high-energy electrons is observed.

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Section: Methodsmentioning

confidence: 99%

RFEA Measurements of High-Energy Electrons in a Helicon Plasma Device with Expanding Magnetic Field

Gulbrandsen

Fredriksen

2017

Front. Phys.

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“…When the probe starts to emit a sufficient number of electrons, the apparent floating potential measured by the probe increases and approaches the plasma potential. As soon as the plasma potential at a given time is reached, the apparent floating potential saturates and a further increase of the heating current only leads to a very small increase of the order of kT e /e [29] which is due to space charge effects. The plasma potential has been obtained from this saturation value without correction of the space charge effects.…”

Section: Methodsmentioning

confidence: 99%

Spatial and temporal development of the plasma potential in differently configured pulsed magnetron discharges

Welzel¹,

Dunger

Liebig

et al. 2008

New J. Phys.

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T h e o p e n -a c c e s s j o u r n a l f o r p h y s i c s Abstract. Time-resolved emissive probe measurements have been performed to study the spatio-temporal development of the plasma potential in an asymmetric bipolar pulsed magnetron discharge. The influence of the substrate potential as well as of the substrate position has been investigated while the further conditions were the same. To access the entire potential range which was between −100 V and + 400 V and to obtain sufficient time-resolution of the emissive probe, different heating currents had to be used. The plasma potential has been found to be typically close to zero in the 'on' phase, about + 40 V in the stable 'off' phase and up to + 400 V at the beginning of the 'off' phase, which is in agreement with the results of other authors. However, the positive values in the 'off' phase are generally lower than those reported and stay mostly below the target potential. This is explained by macroscopic considerations of the quasineutrality of the plasma taking into account a magnetic and geometrical shielding of the target, acting as an anode in the 'off' phase, and the potential and position of the substrate holder and environment. New Journal of Physics

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“…7,8,14 The probe consists of a low work function emitter material which is heated to high enough temperatures to produce a thermionic electron emission current comparable to the ion current that can be drawn from the plasma. When the probe is biased highly negative compared to the local plasma potential the filament will collect ions from the plasma and emit a thermionic electron current, creating an increasingly large apparent ion current as the heater current is increased.…”

Section: Iia Emissive Probesmentioning

confidence: 99%

Magnetic Field Effects on the Plume of a Diverging Cusped-Field Thruster

Matlock¹,

Gildea²,

Hu³

et al. 2010

46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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The Diverging Cusped-Field Thruster (DCFT) uses three permanent ring magnets of alternating polarity to create a unique magnetic topology intended to reduce plasma losses to the discharge chamber surfaces. The magnetic field strength within the DCFT discharge chamber (up to 4 kG on axis) is much higher than in thrusters of similar geometry, which is believed to be a driving factor in the high measured anode efficiencies. The field strength in the near plume region is large as well, which may bear on the high beam divergences measured, with peaks in ion current found at angles of around 30-35 from the thruster axis. Characterization of the DCFT has heretofore involved only one magnetic topology. It is then the purpose of this study to investigate changes to the near-field plume caused by altering the shape and strength of the magnetic field. A thick magnetic collar, encircling the thruster body, is used to lower the field strength outside of the discharge chamber and thus lessen any effects caused by the external field. Changes in the thruster plume with field topology are monitored by the use of normal Langmuir and emissive probes interrogating the near-field plasma. Results are related to other observations that suggest a unified conceptual framework for the important near-exit region of the thruster.

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Effect of space-charge limited emission on measurements of plasma potential using emissive probes

Cited by 116 publications

References 10 publications

RFEA Measurements of High-Energy Electrons in a Helicon Plasma Device with Expanding Magnetic Field

RFEA Measurements of High-Energy Electrons in a Helicon Plasma Device with Expanding Magnetic Field

Spatial and temporal development of the plasma potential in differently configured pulsed magnetron discharges

Magnetic Field Effects on the Plume of a Diverging Cusped-Field Thruster

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