ISIS Penning source extraction studies reveal the 3-dimensional Child–Langmuir effect

We report on a successful test of a new method for intense ion beam formation using an extraction with inhomogeneous electric field. Its key feature is a special shape of the extraction electrodes providing a higher rate of ion acceleration. It is applicable to any ion source type and could be used to improve performance of a wide range of plasma devices. The proof of concept was carried out using a high-current electron-cyclotron resonance ion source SMIS 37. High efficiency of the new extraction and proton beam formation with a record current density of up to 1.1 A cm −2 was demonstrated.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High current ion beam formation with strongly inhomogeneous electrostatic field

Vybin¹,

Izotov²,

Skalyga³

2020

“…Another example comes from the study that inspired this one, where for the first time the 3D CL law was studied experimentally using a plasma ion source [32]. The study used two Penning type negative ion sources (differing by the plasma volume) with total of four different PE aperture sizes and shapes (three slits and one round aperture).…”

Section: Discussionmentioning

confidence: 99%

Critical assessment of the applicability of the Child-Langmuir law to plasma ion source extraction systems

Kosonen

Kalvas

Toivanen

et al. 2023

Self Cite

Applicability of the classical one-dimensional and the recently developed multi-dimensional Child-Langmuir laws to plasma ion source extraction systems is studied. Experiments with a filament-driven multicusp ion source using a simplified extraction system, and comprehensive simulations with two different software packages, suggest that ion beams, which are typically assumed to be space charge or Child-Langmuir limited, are actually divergence-limited. In addition, it was observed that the dynamic plasma meniscus and geometric effects of the extraction system have a greater impact on the ion beam behavior than the effects predicted by the multi-dimensional Child-Langmuir law. Nevertheless, it was found that ion beams produced by the ion source exhibit space charge limited behavior, the beam current scaling with the extraction voltage as $I\propto V^{3/2}$, provided that the entire beam is measured and its divergence is kept small and constant for each extraction voltage. This implies that the applicability of the Child-Langmuir law on a specific extraction system cannot be resolved by a straightforward voltage sweep and beam current measurement but instead, the plasma parameters must be adjusted for each extraction voltage. By shifting the focus from the Child-Langmuir limited framework to the divergence-limited framework, a clearer interpretation of the beam current -- voltage characteristics of extraction systems can be achieved. This shift in perspective may also lead to the development of new design paradigms that can further enhance the performance of plasma ion source extraction systems.

“…Fourth, it should be noted that the new approach to the formation of an ion beam is also applicable to a multicomponent plasma. In particular, when forming a beam of negative ions, it is possible to decrease the power of the co-extracted electron beam [11]. The use of the new approach makes it possible to unleash the potential of those facilities, where the plasma emission ability exceeds the capability of the extraction system [2].…”

Section: Introductionmentioning

confidence: 99%

Experiments on intense ion beam formation with an inhomogeneous electric field

Vybin¹,

Skalyga²,

Izotov³

et al. 2021

The high efficiency of a new ion beam extraction system with a strongly inhomogeneous electric field has been experimentally demonstrated. Previously, this approach was proposed and analysed numerically by the authors. The experiment was carried out using a pulsed high-current electron-cyclotron resonance (ECR) ion source SMIS 37 with high frequency (37.5 GHz) and high power (100 kW) microwave plasma heating. The accelerating field strength is increased (when compared to a flat or a quasi-pierced geometry) in the plasma meniscus region due to its inhomogeneity. It allows for the increase of the ion acceleration rate and for expansion of the available range of current densities with effective ion beam formation. The experiment demonstrated the main advantages of this approach, such as: a significant decrease in the optimal accelerating voltage for certain values of current density; a possibility of ion beam formation with previously inaccessible current densities; a significant decrease in the ion flux to the puller in non-optimal modes of ion beam formation. Proton beams with a current density of up to 1.1 A cm-2 were obtained for the first time with an ECR ion source.