Historical research guide · 0945 · 2009
Deuterium anions in inertial electrostatic confinement devices
D. R. Boris · E. Alderson · G. Becerra · D. C. Donovan · B. Egle · G. A. Emmert · L. Garrison · G. L. Kulcinski · J. F. Santarius · C. Schuff · S. J. Zenobia
In one minute
An inertial electrostatic confinement machine is a vacuum chamber with a see-through wire cage at its centre, held at a hundred thousand volts negative. Deuterium ions fall inwards through the gaps, oscillate through the middle, and some of them fuse. Everyone had assumed the traffic was positive. D. R. Boris and colleagues in Gerald Kulcinski’s group at the University of Wisconsin–Madison put two instruments on their machine — a magnet that sorts charged particles by mass and speed, and a shielded current collector — and found deuterium ions carrying a negative charge streaming out of it. The energy spectra separate how they are made: ions that pick up two electrons from background gas on the way in, and ions built right at the glowing cathode when a slow electron attaches to an excited deuterium molecule. Some survive as whole molecules long enough to fly forty centimetres to the detector. The negative current is not a curiosity — the team estimates about a milliamp of it, flowing in channels set by the cage geometry.
Connection
Chapter 9 studies plasma that organises itself into structure, and this paper shows an inertial electrostatic device sorting its own particles into beams and channels that nobody designed; chapter 12 keeps the ledger of fusion routes, and this is the one an ordinary laboratory can own — instrumented here well enough to reveal a whole population of carriers the standard models of the device had left out.
From the source
Deuterium ions with a negative charge stream out of a gridded inertial electrostatic confinement device in quantity: current densities as high as 8.5 microamps per square centimetre were measured at the wall of the Wisconsin machine, forty centimetres from the cathode surface, with a collector of admittance area 0.7 square centimetres.Abstract; Section II E, Faraday trap results
The energy spectrum taken at a hundred kilovolts resolves five separate populations: three born in the space between the grids when fast positive molecular ions capture electrons from the background gas, and two born at the cathode itself when a slow electron attaches to an excited deuterium molecule.Section II B and II C; Figures 4 and 5, the five-Gaussian fit
Whole molecular anions survive the trip. Their flight distance implies a metastable lifetime of at least about half a microsecond, and the ratio of molecular to atomic anions formed at the cathode came out between 0.5 and 1 — many orders of magnitude above the roughly one-in-a-hundred-thousand ratio reported for caesium-sputter sources, and in line with the 0.35 to 0.4 seen in dielectric barrier discharges.Section II C, Discussion of the magnetic deflection-energy analyzer results
Along the line of sight measured, secondary electrons are the minor part of the outgoing negative current, not the major one: switching on a hundred-gauss deflecting field removed only eighteen per cent of the collected current, and raising it to four hundred gauss removed a further two per cent, showing the remainder is genuinely made of ions.Section II E, Experimental results, Faraday trap
The outgoing negative flow is not uniform but channelled: the potential dips around the individual cathode wires focus anions and electrons into beams, the collected current differed by a factor of five between two viewing positions, and scaling one channel to the 230 openings of the cathode gives a total anion current of roughly 0.5 to 1.5 milliamps.Section II E and Section II E 2; Figures 9, 10 and 12
What to watch: the authors name their own next measurement — a multichannel array of Faraday cups to map the angular structure of the anion and electron beams, which would settle quantitatively how much of the cathode current these negative species carry, and how far the same physics explains the divergent flows seen in other hollow-cathode devices.Section II E 2, closing paragraphs; Section III, Conclusions
The way in
https://doi.org/10.1103/physreve.80.036408How to cite it
D. R. Boris, E. Alderson, G. Becerra, D. C. Donovan, B. Egle, G. A. Emmert, L. Garrison, G. L. Kulcinski, J. F. Santarius, C. Schuff, S. J. Zenobia (2009) Deuterium anions in inertial electrostatic confinement devices doi:10.1103/physreve.80.036408