STM-D-0924Paper2020Published and peer-reviewed

Kinetic characteristics of ions in an inertial electrostatic confinement device

D. Bhattacharjee · N. Buzarbaruah · S. R. Mohanty · S. Adhikari

Abstract and summary · read the original at the source

In one page

An inertial electrostatic confinement machine is the simplest fusion device anyone builds: a vacuum chamber, a see-through wire cage in the middle held at a large negative voltage, and deuterium gas. Ions fall inwards through the gaps in the cage, overshoot, come back, and keep falling through the middle again and again until they hit something. Bhattacharjee and colleagues at the Centre of Plasma Physics in Assam modelled their own tabletop machine particle by particle and set the result against probe measurements made on the same device. The simulation reproduces what the experiment sees: the ions organise themselves into bright spokes through the cage openings, and their own space charge builds a virtual anode inside the real cathode — an electrode made of nothing but trapped ions, with a second, nested one made of electrons appearing at the highest voltages. Core ion density climbs an order of magnitude between one and four kilovolts, and the energy spread of the ions inside the cage tells you which ones are trapped and which are still recirculating.

Why it matters hereChapter 9 is about plasma that organises itself into structure — and the star mode, the virtual anode and the nested virtual cathode of an inertial electrostatic device are that behaviour on a benchtop, with a knob on the front. Chapter 12 keeps the ledger of fusion routes, and this is the one an ordinary laboratory can actually own: the same architecture Philo Farnsworth patented, run as a neutron source and instrumented well enough to be modelled.

What it claims

01Ions recirculating through the openings of the gridded cathode pick out dominant channels rather than filling the volume evenly — the star mode — and the same spokes appear in the simulated phase space and in a photograph taken through the bottom of the chamber during a minus one kilovolt discharge.Section IV, opening; Figure 3(a) and 3(b)
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02Trapped ions build their own electrode: their space charge forms a virtual anode inside the real cathode which reflects later ions before they reach the centre, and the depth of the potential well deepens as the cathode is driven from minus one to minus five kilovolts.Section IV A; Figures 4 and 5(a) to 5(e)
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03Secondary electrons knocked off the grid are themselves trapped by that virtual anode and can form a virtual cathode nested inside it — a second electrode made of nothing but charge — which the experiment shows clearly at minus five kilovolts while the simulation shows only its beginning.Section IV A, discussion of Figure 5(d) and 5(e)
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04The ion density in the core rises an order of magnitude with drive, from 6.3 times ten to the fifteenth per cubic metre at minus one kilovolt to 3.1 times ten to the sixteenth at minus four kilovolts, and the simulated profiles track the probe measurements on the same machine.Section IV A; Figure 7(a) to 7(d)
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05Grid transparency is the design parameter that sets core density: an eight-wire cathode about 92 per cent transparent gives a higher peak core ion density than a sixteen-wire cathode of the same diameter at about 85 per cent, in both the simulation and the experiment.Section IV A, final paragraphs; Figures 8 and 9
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06Inside the cathode the ion energy distribution shifts from a double-Gaussian to a single-Gaussian shape as the voltage rises, the high-energy peak being the trapped population and the low-energy one the ions merely recirculating, so drive converts recirculation into trapping — and resolving the multiple wells above minus four kilovolts is the named next step, needing finite-element or massively parallel particle-in-cell codes rather than the single-processor one used here.Section IV B, Figure 10; Section V, conclusion
What to watch

Read it · abstract

Abstract

The kinetic analyses are quite important when it comes to understanding the particle behavior in any device as they start to deviate from a continuum nature. In the present study, kinetic simulations are performed using the particle-in-cell method to analyze the behavior of ions inside a cylindrical inertial electrostatic confinement fusion (IECF) device which is being developed as a tabletop neutron source. Here, the lighter ions, like deuterium, are accelerated by applying an electrostatic field between the chamber wall (anode) and the cathode (cylindrical gridded wire), placed at the center of the device. The plasma potential profiles obtained from the simulated results indicate the formation of multiple potential well structures inside the cathode grid depending upon the applied cathode potential (from -1 to -5 kV). The ion density at the core region of the device is found to be of the order of 10^(16) m^(-3), which closely resembles the experimental observations. Spatial variation of ion energy distribution function has been measured in order to observe the characteristics of ions at different cathode voltages. Finally, the simulated results are compared and found to be in good agreement with the experimental profiles. The present analysis can serve as a reference guide to optimize the technological parameters of the discharge process in IECF devices.

D. Bhattacharjee, N. Buzarbaruah, S. R. Mohanty and S. Adhikari, Kinetic characteristics of ions in an inertial electrostatic confinement device, Physical Review E 102, 063205 (2020); received 18 September 2020, published 10 December 2020. The work comes from the Centre of Plasma Physics — Institute for Plasma Research at Sonapur, Assam, the Homi Bhabha National Institute in Mumbai, and the Department of Physics at the University of Oslo.

(Abstract only — see the rights note above. On this site, the same group’s experimental study of the discharge plasma in this cylindrical machine is at /library/stm-218a859c1b, deuterium anions in these devices are at /library/stm-27b0684846, space-charge neutralisation in inertial electrostatic plasmas is at /library/stm-5c07c85688, the Defense Intelligence Reference Document on the approach is at /library/stm-cac9786426, and Philo Farnsworth’s founding patent is at /library/stm-3a226d4c01.)

The way in

https://doi.org/10.1103/physreve.102.063205Published as Physical Review E 102, 063205 (2020) under the APS default licence, with no Creative Commons statement, so the sheet stays abstract-only. The full article was read on 2026-09-08 through the APS full-text endpoint at harvest.aps.org, and every claim below is located to a section or figure of it. The abstract is the published one, with the LaTeX superscript braces around the powers in the ion-density figure rendered as parentheses so the page displays.

How to cite it

D. Bhattacharjee, N. Buzarbaruah, S. R. Mohanty, S. Adhikari (2020) Kinetic characteristics of ions in an inertial electrostatic confinement device. doi:10.1103/physreve.102.063205

Where it sits in the curriculum

Plasmoids, charge clusters and the orbs Lattice confinement fusion