Neutron production rate and plasma characteristics of spherically convergent beam fusion
Kunihito Yamauchi · Yasushi Takeuchi · Yutaka Ogino · Masato Watanabe · Akitoshi Okino · Yoshitaka Sunaga · Eiki Hotta
Abstract and summary · read the original at the source
In one page
An inertial-electrostatic confinement device is the simplest fusion machine anyone can build: a wire cage inside a vacuum chamber, held tens of kilovolts negative, so that deuterium ions fall inward through the gaps and meet in the middle. Yamauchi, Takeuchi, Ogino, Watanabe, Okino, Sunaga and Hotta at the Tokyo Institute of Technology built one and measured it properly. Running deuterium at a few millitorr, 40 kilovolts and 2 milliamps, it produced ten thousand neutrons a second, steadily, from a table-top. They then asked the harder question — where are the fusions actually happening — and answered it two ways. The neutron count rises with current a little faster than in a straight line but well short of squared, which says most reactions are fast ions striking slow background gas rather than beam meeting beam. And both a probe pushed into the plasma and a particle simulation show the same thing: a second potential hill, a virtual anode, standing in the very centre.
Why it matters hereChapter 12 is the ledger of fusion routes, and this is the cheapest working one: real deuterium-deuterium neutrons out of a wire cage and a power supply, characterised well enough to say which collisions produced them. Chapter 9 gets the virtual anode — a plasma building its own potential structure in mid-air and holding it — measured and simulated in the same paper.
What it claims
01The device is a 45 cm diameter, 31 cm high stainless-steel cylindrical chamber holding a 30 cm spherical mesh anode and, inside it, an open spherical grid cathode 5 cm across made of 2.0 mm stainless-steel wire, run on hydrogen or deuterium at a steady 1 to 15 millitorr.Abstract; Section 2, Fig. 2 and Fig. 3
Published and peer-reviewed02With deuterium, a steady-state neutron production of ten thousand per second was measured at a discharge of 40 kilovolts and 2 milliamps, using a helium-3 counter mounted 25 cm above the device centre and converting the dose rate on the assumption that emission is spherically symmetric.Abstract; Section 3.3, Figs. 7 and 8
Published and peer-reviewed03Both the electrostatic-probe measurement and the particle simulation confirm that a virtual anode forms in the central part inside the grid cathode — a second potential structure, built by the space charge of the converging ions themselves, that traps and re-focuses them.Abstract; Section 3.2, Fig. 6 and Section 4.2, Fig. 10
Published and peer-reviewed04Neutron production rises with cathode voltage along the curve expected from the deuterium-deuterium reactivity if every reaction were a beam ion striking background gas with kinetic energy equal to the applied cathode voltage; the measurement follows that curve fairly closely.Section 3.3, Fig. 7
Published and peer-reviewed05Neutron production scales as roughly the 1.3 power of discharge current, which sits between the linear scaling of beam-background reactions and the quadratic scaling of beam-beam reactions. Fitting the rate as a linear term plus a quadratic term and plotting the ratio of the two against cathode voltage shows the beam-background share growing as the voltage rises, and shows that below about 4 milliamps in this device beam-background reactions dominate: beam-beam collisions have the larger cross-section but happen only in a very small volume near the centre.Section 3.3, Eq. 1 with Figs. 8 and 9
Published and peer-reviewed06The particle simulation is one-dimensional in position and two-dimensional in velocity, using ten thousand superparticles each for ions and electrons started from a uniform density with a Maxwellian spread, at 0.026 eV for ions and 2.0 eV for electrons; spherical symmetry lets the self-generated magnetic field cancel and be neglected. The measured Paschen curve also shows deuterium breaking down at roughly twice the voltage of hydrogen at the same pressure-times-distance.Section 4.1, Table 1 and Section 3.1, Fig. 5
Published and peer-reviewed
Read it · abstract
Abstract
AbstractExperimental and simulation results of a spherical glow discharge for a portable neutron source are presented. The experimental device is a 45‐cm‐diameter, 31‐cm‐high stainless‐steel cylindrical chamber, in which a spherical mesh‐type anode 30 cm in diameter is installed. The spherical grid cathode consists of 2.0‐mm‐diameter stainless‐steel wire, which is made into an open spherical grid of 5‐cm diameter. The system is maintained at a constant pressure of 1 to 15 mTorr by feeding hydrogen or deuterium gas. The basic characteristics of breakdown voltages versus pressure and electrostatic potential profiles were measured for hydrogen discharge. Using deuterium, a steady‐state neutron production of 104 s–1 was observed at a discharge of 40 kV, 2 mA. Motions of ions and electrons in the device were simulated by using a particle code, which is one‐dimensional in coordinate system and two‐dimensional in velocity space. It was confirmed by both the measurement and simulation that a virtual anode is formed in the central part inside the grid cathode. © 2001 Scripta Technica, Electr Eng Jpn, 135(2): 1–8, 2001
Kunihito Yamauchi, Yasushi Takeuchi, Yutaka Ogino, Masato Watanabe, Akitoshi Okino, Yoshitaka Sunaga and Eiki Hotta, Neutron production rate and plasma characteristics of spherically convergent beam fusion, Electrical Engineering in Japan 135, issue 2, 1–8 (2001), translated from IEEJ Transactions on Fundamentals and Materials 120, issue 4, 420–426 (2000). The work was done at the Tokyo Institute of Technology.
(Abstract only — see the rights note above. On this site, Bhattacharjee and colleagues on the kinetic characteristics of ions in an inertial electrostatic confinement device are at /library/stm-0b806244cb, Evstatiev and colleagues on space-charge neutralization in inertial electrostatic confinement plasmas is at /library/stm-5c07c85688, Boris and colleagues on deuterium anions in these devices is at /library/stm-27b0684846, Buzarbaruah and colleagues on discharge plasma in a cylindrical device is at /library/stm-218a859c1b, and the Defense Intelligence Agency reference document on inertial electrostatic confinement fusion is at /library/stm-cac9786426.)
The way in
https://doi.org/10.1002/eej.1The English version is Electrical Engineering in Japan 135, issue 2, pages 1 to 8 (2001), a Scripta Technica translation published by Wiley, copyright 2001, with no open licence recorded; Wiley’s PDF refuses automated requests, so the sheet is abstract-only and no text beyond the deposited abstract is reproduced. The Japanese original — Yamauchi and colleagues, IEEJ Transactions on Fundamentals and Materials 120, issue 4, pages 420 to 426 (2000), DOI 10.1541/ieejfms1990.120.4_420 — is openly readable on J-STAGE and was fetched and read there on 2026-09-08, carrying the same English abstract plus the figures; every claim below is located to a section, equation, table or figure of that original. Two defects in the deposited English abstract are left exactly as deposited and corrected in the claims instead: the word Abstract is run together with the first word of the text, and the neutron rate printed as 104 s-1 is ten to the fourth per second, as both the original’s own English abstract and its Figs. 7 and 8 confirm. Affiliation for all seven authors: Tokyo Institute of Technology.
How to cite it
Kunihito Yamauchi, Yasushi Takeuchi, Yutaka Ogino, Masato Watanabe, Akitoshi Okino, Yoshitaka Sunaga, Eiki Hotta (2001) Neutron production rate and plasma characteristics of spherically convergent beam fusion. doi:10.1002/eej.1
Where it sits in the curriculum
Lattice confinement fusionPlasmoids, charge clusters and the orbs