Historical research guide · 1074 · 1991

A Light Ion Beam Driver for the Laboratory Microfusion Facility

J. J. Ramirez · K. R. Prestwich · R. W. Stinnett · D. L. Johnson · C. L. Olson · G. O. Allshouse · M. J. Clauser · V. Harper-Slaboszewicz · T. W. L. Sanford · J. D. Boyes · T. A. Mehlhorn · L. J. Lorence · D. L. Hanson · M. E. Cuneo · R. R. Peterson · R. L. Engelstad · J. W. Powers · H. Y. Khater · M. E. Sawan · E. G. Lovell · G. A. Moses

In one minute

In October 1990 a Sandia National Laboratories team led by J. J. Ramirez, with colleagues from the University of Wisconsin, set out the engineering of a machine that would light a fusion pellet with beams of lithium ions rather than lasers. The Laboratory Microfusion Facility was planned to get 200 to 1000 megajoules of fusion yield out of about 10 to 20 megajoules put into a target the size of a peppercorn. Their driver is 36 pulsed-power accelerators, each a relative of Sandia’s Hermes III machine, fired in a choreographed six-six-twenty-four sequence so three shaped pushes land in turn. Every module accelerates lithium ions across a ring-shaped diode and ramps the voltage as it goes, so the tail of each beam catches the head over the four metres to the target and the pulse squeezes down to fifteen billionths of a second. A magnetic lens at the chamber wall then focuses the beam onto a one-centimetre pellet. The paper is a status report: what is designed, what has been measured, and what still has to be shown.

Connection

Chapter 12 is about getting a very large amount of energy out of a very small amount of fuel, and this is the pulsed-power route to it — no lasers, no magnetic bottle, just capacitors, induction cavities and ions arriving in step. Chapter 9 is about intense, self-organising plasma, and the applied-magnetic-field ion diode described here is one of the most extreme plasma devices ever built: tens of millions of volts across a few centimetres, with the electrons held back by a magnetic field so that only the ions cross.

From the source

The Laboratory Microfusion Facility was planned to develop high-gain, high-yield inertial confinement fusion targets returning 200 to 1000 megajoules, for nuclear weapons effects simulation, thermonuclear weapons physics and energy production, and a 1000-megajoule yield was expected to require about 10 to 20 megajoules of input energy delivered to the target.Abstract; section I, Introduction
The driver concept is 36 accelerator modules driving independent lithium-ion diodes: twelve Hermes-III-sized modules producing a 40-nanosecond beam ramping from 18 to 20 megaelectronvolts at 0.46 to 0.72 megamperes, and twenty-four high-energy modules ramping from 26 to 32 megaelectronvolts at 0.8 to 1.2 megamperes, with the ramp making each beam bunch over the four-metre transport so the power pulse at the target shortens to 15 nanoseconds and about 16 megajoules arrives inside a two-centimetre diameter.Section I, Introduction
The module technology already exists: Hermes III is a 22-megavolt, 730-kiloampere, 40-nanosecond generator that adds eighty pulse-forming modules through induction cavities and a magnetically insulated transmission line, positive-polarity operation was demonstrated on Hermes III and HELIA simply by rotating the twenty induction cavities, and an analysis of measured Hermes III performance indicates the twenty-four high-power modules can be synchronised to within an acceptable two-nanosecond window.Section II, Accelerator Modules
The diode is the hard part and the authors say so: the required 25 to 32 ohm operating impedance is higher than other high-power ion diodes have been tested at, the 27 to 32 megavolt diode voltage is beyond the existing experimental database and will need larger anode-cathode gaps and higher insulating magnetic fields, and where a beam microdivergence of about 14 milliradians is acceptable for an ignition experiment on PBFA II, this 16-megajoule design needs about 6 milliradians.Section III, Lithium Ion Diode
Focusing is done by a two-lens achromatic system — the beam’s own magnetic field in the diode working with a 30-centimetre solenoidal lens centred 1.65 metres from the target — with one torr of helium providing charge and current neutralisation; particle-in-cell simulations with the code PICDIAG predict 90 percent energy and 148 percent power transport efficiency for a beam of zero microdivergence, and 60 percent energy and 106 percent power transport efficiency at a half-width-at-half-maximum microdivergence of 6 milliradians.Section IV, Beam Transport and Focusing
A research programme to validate the concept was under way: applied-magnetic-field extraction ion diode experiments on the new SABRE accelerator at about 3 megavolts matched the theoretical model that also describes the PBFA II barrel diode and transitioned to enhanced ion flow in less than five nanoseconds, SABRE was to reach 10 megavolts by December 1990, and a successful sub-scale test there would be followed by a full-scale demonstration on Hermes III.Section VI, Technology Validation Program

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https://doi.org/10.13182/fst91-a29420

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

WHAT IS REPRODUCED. The version of record is Fusion Technology volume 19, issue 3 part 2A, pages 664 to 668, May 1991, published for the American Nuclear Society and held closed by Informa UK Limited; that version is cited here and is not the copy reproduced below. The text below is the Sandia National Laboratories conference release SAND-90-1445C, CONF-901007-31, prepared for the ninth topical meeting on the technology of fusion energy at Oak Brook, Illinois, 7 to 11 October 1990, under United States Department of Energy contract DE-AC04-76DP00789, and distributed by the Office of Scientific and Technical Information as record 6376642 and DE91 005313. Page one carries the MASTER stamp and the line DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED, the closing page carries the standard Department of Energy disclaimer, and the document bears no copyright notice, so the complete text is reproduced here. It was downloaded from osti.gov/servlets/purl/6376642 on 2026-09-08 and read in full, page images included. HOW IT WAS READ AND WHAT WAS FIXED. The scan carries a text layer of uneven quality; the transcription below was checked against the page images at 140 dots per inch. Three optical-character-recognition artefacts were corrected: the diode impedance printed as ohms had been read as the letters ft, the beam-divergence sign had been read as a stray glyph, and the reference-number superscripts scattered through the running text have been dropped, since the numbered reference list is reproduced in full at the end. Inequality signs are written out in words. TWO DEFECTS THAT BELONG TO THE SOURCE, NOT THE TRANSCRIPTION. First, in the list of beam-focus degradation mechanisms in section four the original names four items but the sentence that follows refers to items one, four and five; that mismatch is in the printed document. Second, the subscript on the letter E in item four of the same list did not survive the scan and is left unmarked rather than guessed at. The figures and their caption page are images and are not reproduced. Companion sheets: the programme statement for light-ion inertial confinement fusion at /library/stm-102f44df48, the PBFA II ion diode theory this driver builds on at /library/stm-a14b16230b, and the international status review of the same period at /library/stm-b23ae31c98.

How to cite it

J. J. Ramirez, K. R. Prestwich, R. W. Stinnett, D. L. Johnson, C. L. Olson, G. O. Allshouse, M. J. Clauser, V. Harper-Slaboszewicz, T. W. L. Sanford, J. D. Boyes, T. A. Mehlhorn, L. J. Lorence, D. L. Hanson, M. E. Cuneo, R. R. Peterson, R. L. Engelstad, J. W. Powers, H. Y. Khater, M. E. Sawan, E. G. Lovell, G. A. Moses (1991) A Light Ion Beam Driver for the Laboratory Microfusion Facility doi:10.13182/fst91-a29420

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