Influence of electron impact ionization on the efficiency of thermoemission ion source

2011

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A Monte Carlo method-based model of a hot cavity surface ion source with a spherically shaped ionizer is presented. A numerical code enables studies of ion source efficiency as a function of an extraction voltage, geometry of the ionizer and its temperature, the size of extraction aperture and many other factors. The calculation results for a variety of mentioned parameters are presented. A novel configuration of surface ion source is proposed and discussed -the efficiency of the source with an almost spherically shaped ionizer could be much higher than that of currently used constructions of ion sources.

Section: Introductionmentioning

confidence: 74%

Modeling of Ionization in a Spherical Surface Ionizer

2011

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“…This is done using the successive over-relaxation method as in papers [16,17,[26][27][28][29][30]. Electric field is calculated by numerical derivation of the potential.…”

Section: Two-dimensional Simulations Of H − Ions Extraction 255mentioning

confidence: 99%

Two-Dimensional Simulations of H^-Ions Extraction

2017

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The 2D particle-in-cell method based model of a negative ion source is presented. The spatial distributions of electrostatic potential and plasma component densities are presented. Changes of negative ion distribution and potential as well as the extracted H − current with the plasma grid bias voltage are investigated. The presence of the potential well near the plasma grid surface that traps the negative ions is shown. Increase of the H − ions density inside the chamber with the negative bias voltage is demonstrated. Influence of the H − ion flux outgoing from the plasma grid on the extracted current was checked: increase by factor 2 is observed when the flux rises 4 times. Current-voltage characteristics of the ion source are presented, saturation of the curve is observed above 50 kV

“…It is based on the assumption that multiple collisions of atoms with the hot ioniser walls could lead to high ion source ionisation efficiency. Electron impact ionisation was also proven to bring very important contribution for high ioniser temperatures and in the case of hard-to-ionise elements [14]. Several modifications were made to take into account radioactive decay of nuclides and delays due to the diffusion out of the target as well as effusion delay (related to sticking of particles to the ioniser walls) [15,16].…”

Section: Introductionmentioning

confidence: 99%

Ionisation Efficiency in Conical Hot Cavities

2017

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Surface ionisation in a new type of hot cavity characterised by the shape of a truncated cone is considered in the paper. Influence of the hot cavity shape and its temperature on the ionisation efficiency of stable and long-lived nuclides is under investigation and the supremacy of elongated conical cavities is proven. The role of the extraction opening size is studied and its optimal diameter (≈ 1 mm) is found for the considered cavity shapes. It is shown that the extraction voltages of 1-2 kV are large enough to obtain high efficiencies and saturation of the current-voltage curves is observed above these values. Changes of ionisation effciency with the ioniser temperature are investigated -increase of ion yield with T is observed. It was proven that cold spots inside the ioniser cavity (near the extraction opening -in the considered case) can degrade ion source performance by several tens percent.