Transport of negative ions across a double sheath with a virtual cathode

McAdams, R.; Holmes, Andrew; King, D.; Surrey, E.

doi:10.1088/0963-0252/20/3/035023

Cited by 55 publications

(60 citation statements)

References 24 publications

(63 reference statements)

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“…Negative ions created by atoms on the caesiated surface are transported across the virtual cathode 12 and sheath into the plasma. Those from the bulk plasma enter the meniscus to form a well ordered beam.…”

Section: Fig 2 (Color Online) Beam Formation In a Caesiated Negatimentioning

confidence: 99%

Beyond ITER: Neutral beams for a demonstration fusion reactor (DEMO) (invited)

McAdams

2014

Review of Scientific Instruments

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(Presented XXXXX; received XXXXX; accepted XXXXX; published online XXXXX) (Dates appearing here are provided by the Editorial Office)In the development of magnetically confined fusion as an economically sustainable power source, ITER is currently under construction. Beyond ITER is the DEMO programme in which the physics and engineering aspects of a future fusion power plant will be demonstrated. DEMO will produce net electrical power. The DEMO programme will be outlined and the role of neutral beams for heating and current drive will be described. In particular, the importance of the efficiency of neutral beam systems in terms of injected neutral beam power compared to wallplug power will be discussed. Options for improving this efficiency including advanced neutralisers and energy recovery are discussed.

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Section: Fig 2 (Color Online) Beam Formation In a Caesiated Negatimentioning

confidence: 99%

Beyond ITER: Neutral beams for a demonstration fusion reactor (DEMO) (invited)

McAdams

2014

Review of Scientific Instruments

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“…It has been extended to include virtual cathode formation. 12 Only the outline of the model and the main results will be given here.…”

Section: The Sheath Modelmentioning

confidence: 99%

“…The emitted current density is j b and the maximum transported current density is j bmax . The method of solution [10][11][12] of Poisson's equation is to initially solve the equation up to the space charge limit. This allows the maximum transported current density j bmax before the formation of a virtual cathode to be calculated.…”

Section: The Sheath Modelmentioning

confidence: 99%

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Sheath structure in negative ion sources for fusion (invited)

McAdams

King

Holmes³

et al. 2012

Review of Scientific Instruments

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In fusion negative ion sources, the negative ions are formed on the caesiated plasma grid predominantly by hydrogen atoms from the plasma. The space charge of the negative ions leaving the wall is not fully compensated by incoming positive ions and at high enough emission a virtual cathode is formed. This virtual cathode limits the flux of negative ions transported across the sheath to the plasma. A 1D collisionless model of the sheath is presented taking into account the virtual cathode. The model will be applied to examples of the ion source operation. Extension of the model to the bulk plasma shows good agreement with experimental data. A possible role for fast ions is discussed.

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“…In negative hydrogen ion sources, a virtual cathode can be present in the PG sheath, 18,19 also affecting the electron dynamics from the plasma onto the PG surface. Since the plasma potential at BATMAN can be determined in the bulk plasma only, the PG sheath potential difference is used for the description of the sheath property, neglecting the presence of a virtual cathode.…”

Section: Introductionmentioning

confidence: 99%

Extraction of negative charges from an ion source: Transition from an electron repelling to an electron attracting plasma close to the extraction surface

Wimmer

Fantz

NNBI-Team³

2016

Journal of Applied Physics

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Large-scale sources for negative hydrogen ions, capable of delivering an extracted ion current of several ten amperes, are a key component of the neutral beam injection system of the upcoming ITER fusion device. Since the created heat load of the inevitably co-extracted electrons after magnetic separation from the extracted beam limits their tolerable amount, special care must be taken for the reduction of coextracted electrons -in particular in deuterium operation, where the larger amount of co-extracted electrons often limits the source performance. By biasing the plasma grid (PG, first grid of the extraction system) positively with respect to the source body the plasma sheath in front of the PG can be changed from an electron repelling towards an electron attracting sheath. In this way, the flux of charged particles onto the PG can be varied, thus changing the bias current and inverse to it the amount of co-extracted electrons. The PG bias affects also the flux of surface-produced H − towards the plasma volume as well as the plasma symmetry in front of the plasma grid, strongly influenced by an ⃗ E × ⃗ B drift. The influence of varying PG sheath potential profile on the plasma drift, the negative hydrogen ion density and the source performance at the prototype H − source is presented, comparing hydrogen and deuterium operation. The transition in the PG sheath profile takes place in both isotopes, with a minimum of co-extracted electrons formed in case of the electron attracting PG sheath. The co-extracted electron density in deuterium operation is higher than in hydrogen operation, which is accompanied by an increased plasma density in deuterium.

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Transport of negative ions across a double sheath with a virtual cathode

Cited by 55 publications

References 24 publications

Beyond ITER: Neutral beams for a demonstration fusion reactor (DEMO) (invited)

Beyond ITER: Neutral beams for a demonstration fusion reactor (DEMO) (invited)

Sheath structure in negative ion sources for fusion (invited)

Extraction of negative charges from an ion source: Transition from an electron repelling to an electron attracting plasma close to the extraction surface

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