A small electrostatic retarding field energy analyzer with compensating differentiation circuit

Oertl, M.; Störi, H.; Hatakeyama, Rikizo

doi:10.1063/1.327841

Cited by 4 publications

(4 citation statements)

References 13 publications

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“…Comparison of an ISP with an end loss ion spectrometer in the TMX-U mirror machine matched with no auxiliary heating, while the ISP measured hotter ion temperature during ion cyclotron resonance heating-a strong indication that it measures the perpendicular ion energy component [17]. Use of a gridded ISP allowed the probe to be used like an RFA and measure the parallel ion energy distribution by turning the probe into the magnetic field [25]. In a steady plasma the parallel and perpendicular distributions matched.…”

Section: Isp Probesmentioning

confidence: 99%

“…The I -V characteristics of some ISPs show no signs of space charge [16,17,25]. While the I -V characteristics of other ISPs indicate net collected electrons (e.g.…”

Section: Isp and Lp Plasma Potentialmentioning

confidence: 99%

“…(1) They are a classic ISP having only a guard electrode and a collector. Some ISPs have an insulating guard (BPP) [23], an additional electrode for secondary electron control [16,17,22], or a grid over the guard [13,16,25,37], all of which could influence the particle trajectories within the probe in different ways. (2) The probe collected only net ion current over its entire bias range.…”

Section: E × B Drift Of Electrons Into the Probe Volumementioning

confidence: 99%

“…An addition to the ISP design that could help ameliorate space charge is placement of a grid over the guard. This has been done with four ISPs [13,16,25,37], however none of them took full advantage of the ability of the grid to reduce the effects of space charge. A grid with spacing on order the electron Larmor radius would effectively eliminate electrons from entering the probe volume behind the grid.…”

Section: Design Of Isps For Space Chargementioning

confidence: 99%

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Space-charge limits of ion sensitive probes

Brunner

LaBombard

Ochoukov

et al. 2013

Plasma Phys. Control. Fusion

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Ion sensitive probes (ISPs) are used to measure ion temperature and plasma potential in magnetized plasmas. Their operation relies on the difference in electron and ion Larmor radii to preferentially collect the ion species on a recessed electrode. Because of their simple two-electrode construction and optimal geometry for heat flux handling they are an attractive probe to use in the high heat flux boundary of magnetic confinement fusion experiments. However, the integrity of its measurements is rarely, if ever, checked under such conditions. Recent measurements with an ISP in the Alcator C-Mod tokamak have shown that its ion current is space-charge limited and thus its current-voltage (I -V ) response does not contain information on the ion temperature. We numerically solve a 1D Vlasov-Poisson model of ion collection to determine how much bias is needed to overcome space-charge effects and regain the classic I -V characteristic with an exponential decay. Prompted by the observations of space charge in C-Mod, we have performed a survey of ISP measurements reported in the literature. Evidence of space-charge limited current collection is found on many probes, with few authors noting its presence. Some probes are able to apparently exceed the classic 1D space-charge limit because electrons can E × B drift into the probe volume, partially reducing the net ion charge; it is argued that this does not, however, change the basic problem that space charge compromises the measurement of ion temperature. Guidance is given for design of ISPs to minimize the effects of space charge.

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Section: Isp Probesmentioning

confidence: 99%

“…The I -V characteristics of some ISPs show no signs of space charge [16,17,25]. While the I -V characteristics of other ISPs indicate net collected electrons (e.g.…”

Section: Isp and Lp Plasma Potentialmentioning

confidence: 99%

Section: E × B Drift Of Electrons Into the Probe Volumementioning

confidence: 99%

Section: Design Of Isps For Space Chargementioning

confidence: 99%

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Space-charge limits of ion sensitive probes

Brunner

LaBombard

Ochoukov

et al. 2013

Plasma Phys. Control. Fusion

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Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

Brunner

LaBombard

Ochoukov

et al. 2013

Review of Scientific Instruments

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A new Ion Sensitive Probe head has been created for the outer-midplane scanning probe system on the Alcator C-Mod tokamak. The new probe head contains three elements: an ion sensitive probe to measure ion temperature and plasma potential, a Langmuir probe to measure electron temperature, density, and floating potential, and a second Langmuir probe to measure ion saturation current and the density fluctuations arising from ''blob'' events. The ion sensitive probe current is normalized to this measurement to reduced deleterious effects of the strong fluctuations. Design of the high heat flux probe (>100 MW/m(2)) and initial results are presented.

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Comparative measurements of plasma potential with ball-pen and Langmuir probe in low-temperature magnetized plasma

et al. 2015

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The ball-pen probe (BPP) is used for direct plasma potential measurements in magnetized plasma. The probe can adjust the ratio of the electron and ion saturation currents Isat−/Isat+ to be close to one and therefore its I-V characteristic becomes nearly symmetric. If this is achieved, the floating potential of the BPP is close to the plasma potential. Because of its rather simple construction, it offers an attractive probe for measurements in magnetized plasma. Comparative measurements of plasma potential by BPPs of different dimensions as well as one Langmuir probe (LP) in an argon discharge plasma of a cylindrical magnetron were performed at various experimental conditions. An additional comparison by an emissive probe was also performed. All these types of probes provide similar values of plasma potential in a wide range of plasma parameters. Our results for three different BPP dimensions indicate that the BPP can be operated in a cylindrical magnetron DC argon discharge if the value of the ratio of the magnetic field and neutral gas pressure, B/p, is greater than approximately 10 mT/Pa.

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A small electrostatic retarding field energy analyzer with compensating differentiation circuit

Cited by 4 publications

References 13 publications

Space-charge limits of ion sensitive probes

Space-charge limits of ion sensitive probes

Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

Comparative measurements of plasma potential with ball-pen and Langmuir probe in low-temperature magnetized plasma

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