Historical research guide · 1039 · 1987

PBFA II ion diode theory and implications

J. P. VanDevender · S. A. Slutz · D. B. Seidel · R. S. Coats · P. A. Miller · C. W. Mendel Jr. · J. P. Quintenz

In one minute

The Particle Beam Fusion Accelerator II was Sandia’s attempt to drive fusion with ions instead of lasers, and everything depended on one component: the diode, a gap a couple of centimetres wide across which a vast voltage pulse tears lithium ions and throws them at a target. Sandia’s later measurements on the same machine describe what that gap has to deliver — a lithium beam of some ten million volts carrying six to nine trillion watts, in a pulse lasting twenty billionths of a second. J. Pace VanDevender and his Sandia colleagues report two things here. Their two-dimensional particle-in-cell simulations, which follow individual charges in the full electromagnetic field, gave them confidence in the diode designs for the new machine. But the measurements from the earlier accelerators did not fit the accepted picture, in which the gap slowly closes as plasma expands into it. So they built a new model of how the diode really behaves, and used it to say how its impedance could be controlled.

Connection

Chapter 9 is about what dense, self-organising plasma actually does when you drive it hard, and a pulsed-power ion diode is that question in its most demanding engineering form — the behaviour of the plasma in the gap is the machine. Chapter 12 gets the wider point: this is one of the two great routes to inertial fusion, and the reason the light-ion line is worth knowing is that the physics that decided its fate was the physics of a few centimetres of driven plasma.

From the source

Fully electromagnetic, relativistic, two-dimensional particle-in-cell simulations were run for both barrel-type and extractor-type Applied-B ion diodes, and the results increased the team’s confidence in the design of the present and future diodes for the Particle Beam Fusion Accelerator II.Abstract, first sentence
The data from the various experiments on the Proto I, Proto II and PBFA I Applied-B ion diodes are inconsistent with the previous models of diode operation, which explained the machine’s behaviour by anode-cathode gap closure from expanding plasmas.Abstract, second sentence
A new model of diode operation has been devised in place of the gap-closure picture, and applied to the PBFA II diode.Abstract, third sentence
The new model accounts for the diode impedance and for its time history — that is, for how the load the machine sees changes across the pulse, which is what decides how much of the stored energy reaches the beam.Abstract, third sentence
The model also suggests methods for controlling the impedance, turning a diagnosis into a design lever for the driver.Abstract, closing clause
The work was carried out at Sandia National Laboratories for the light-ion inertial confinement fusion programme and issued as report SAND-86-1756C under Department of Energy contract AC04-76DP00789, for the 2nd International Topical Symposium on Inertial Confinement Fusion Research by High-Power Beams in Nagaoka, Japan, June 1986.Title page and report identification, SAND-86-1756C, CONF-8606131-3

The way in

https://doi.org/10.1017/s0263034600002925

Historical source-access record. This guide links to the original; it does not reproduce the paper text.

SOURCE PARTLY REACHED. Published as Laser and Particle Beams 5 (1987), copyright Cambridge University Press, which is closed at the publisher, so no text of the journal article is reproduced here and none was read. The work was first issued as Sandia National Laboratories report SAND-86-1756C, conference number CONF-8606131-3, ten pages, prepared under United States Department of Energy contract AC04-76DP00789 and presented at the 2nd International Topical Symposium on Inertial Confinement Fusion Research by High-Power Beams, Nagaoka, Japan, 16 June 1986. That report is indexed by the Office of Scientific and Technical Information as record 5517025 but no full-text copy is served there, and no copy was reached elsewhere. The abstract below is the one Sandia deposited with the Department of Energy for that report — a United States Government document — and it is word-for-word the abstract the publisher deposited with Crossref, except that the publisher’s copy carries a scan artefact reading ‘Pro to I’ where the government copy reads ‘Proto I’. Every claim locator below points to that abstract, never into the body of the paper. Background for the summary was read from a later, freely available Sandia paper on the same machine — Bailey, Carlson, Filuk, Johnson, Lake, McGuire, Mehlhorn, Pointon, Renk and Maron, ‘Charged particle dynamics in the acceleration gap of the PBFA II ion diode’, OSTI record 10175969, a United States Government document — which is where the beam parameters quoted in the summary come from; it is named as background and none of its findings are stated here as claims of this paper.

How to cite it

J. P. VanDevender, S. A. Slutz, D. B. Seidel, R. S. Coats, P. A. Miller, C. W. Mendel Jr., J. P. Quintenz (1987) PBFA II ion diode theory and implications doi:10.1017/s0263034600002925

Where it sits in the curriculum

Fusion machines: pinches, focus devices and inertial drivers