Historical research guide · 0964 · 1999

Fielding of the on-axis diagnostic package at Z

M. J. Hurst · T. J. Nash · M. Derzon · J. W. Kellogg · J. Torres · J. McGurn · J. Seaman · D. Jobe · S. E. Lazier

In one minute

The Z accelerator at Sandia National Laboratories drives nearly twenty million amps through a wire array and turns it into more than 1.8 million joules of soft x-rays in under ten billionths of a second. M. J. Hurst, T. J. Nash, M. Derzon and their colleagues at Sandia and K-tech describe how you get an instrument close enough to watch that happen from directly overhead. Viewing the pinch from the side was routine; looking straight down the axis meant lowering a package of x-ray cameras, spectrometers and calorimeters into the middle of the machine, where every shot throws off metal fragments with the punch of pistol slugs, a mechanical shock of one to two hundred times gravity, a hard bremsstrahlung flash and an electromagnetic pulse — and then having it cleaned, refitted and realigned for the next day’s shot. Their answer is layered sacrificial armour, heavy-walled lines of sight, a fast valve in front of the detector and a gimbal stiff enough to hold alignment through the blast. Both the instruments and the data survived.

Connection

Chapter 9 is about plasma driven into a shape that holds, and the Z pinch is where that is done at the largest scale anywhere. This paper is the reason the results from it can be trusted: it is the axial view that made the implosion visible at all, and the engineering that kept the instruments alive to record it.

From the source

The Z accelerator produces more than 1.8 megajoules of soft x-rays in less than ten nanoseconds with nearly 20 megaamps flowing through the diode, and the byproducts of that operation — an electromagnetic pulse, a high-energy bremsstrahlung field, mechanical shock and debris — set the environment any instrument near the target has to survive.Section I, Introduction, first paragraph; Figure 1a
A reentrant package lowered into the centre of the machine can hold a full x-ray diagnostic suite on direct lines of sight down the pinch axis — twelve instruments in all, among them two gated pinhole cameras at one-third and two-thirds target magnification, a filtered x-ray diode, time-resolved and one-dimensional imaging spectrometers, a bolometer, a calorimeter, a zero-degree shadowgraphy and optical-attenuation channel, a long focal length microscope and an illumination laser — returning target hydrodynamics, temperature and symmetry at viewing angles of zero, six and nine degrees.Section I, Introduction, closing paragraph; Table 1; Figure 3
The axial view showed pinch physics that side-on diagnostics could not reach: a two-nanosecond framing camera image of a tungsten wire array imploding onto a gold annulus carries a nine-fold symmetry pattern, imprinted by the nine diagnostic slots used to view the pinch from the side. The instrumentation ports are themselves perturbing the implosion.Section I, Introduction, third paragraph; Figure 2
The hardest hazard to design against is the shrapnel plume thrown up the axis: fragments of the equivalent size of 45 calibre slugs, fast enough to cut quarter-inch-deep gouges in the stainless steel vacuum chamber wall. The mitigation is distance plus layered sacrificial armour — a 36-inch cylindrical cover with a half-inch copper top plate, a second stainless shield beneath the package, four further barriers inside the instrument, a 0.010-inch titanium pinhole plate, and a large-aperture fast valve at the detector as the last line of defence.Section: The Environment at Z, paragraphs 1 to 4
It worked. Across the initial ten-shot series no shrapnel damage occurred beyond the pinhole aperture plate; the worst single event was a dimple in a stainless steel debris shield inside a camera. The recurring problem was not impact but deposition — a film of vaporised metal reaching as far as the pinhole plate and occasionally obscuring the 80-micron pinholes, which made the aperture plates consumables.Section: The Environment at Z, paragraphs 4 and 5; Table 1, Maintenance column
What to watch: the shock loading was designed against an estimate rather than a measurement — the shock wave forces were put at 100 to 200 times gravity with no measurements made at the time of design, and the accelerator’s emitted electromagnetic spectrum and intensity had not been quantified either, so double-shielded cables, short runs and faraday enclosures were used in place of a specification. Both are numbers a later campaign can measure directly.Section: The Environment at Z, the mechanical shock and electromagnetic pulse paragraphs

The way in

https://doi.org/10.1063/1.1149377

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 Review of Scientific Instruments volume 70, issue 1, pages 468 to 470, January 1999, published by the American Institute of Physics under its own terms; that version is cited here and is not the copy reproduced below. The text below is the Sandia National Laboratories conference release SAND-98-1282C, CONF-980605, prepared for the twelfth topical conference on high-temperature plasma diagnostics at Princeton, New Jersey, 7 to 11 June 1998, under United States Department of Energy contract DE-AC04-94AL85000, and distributed by the Office of Scientific and Technical Information as record 672045 and DE98005524. Its own cover carries the statement that distribution of the document is unlimited, and it bears no copyright notice, so the complete text is reproduced here. It was downloaded from osti.gov/servlets/purl/672045 on 2026-09-08 and read in full. HOW IT WAS READ. The scan carries no text layer at all: the ten pages were rasterised at 300 dots per inch and put through optical character recognition, and the transcription was then checked against the page images. TWO THINGS TO KNOW ABOUT THE TEXT. First, several inch dimensions are missing from the source document itself, not from the transcription — where a fraction was meant to print, the original shows only a blank low line, and those blanks are reproduced as printed rather than guessed at. Second, the conference release and the published article differ in a few words of the abstract: the release lists EMP among the hazards and says which was fielded and in this paper, where the journal version drops EMP and reads fielded and in this article. The release is transcribed as it stands. Its own typographic slips, including Shodowgraphy and Angar in Table 1 and likely hood in the shrapnel section, are also left as printed. Greater-than and less-than signs are written out in words because this page’s format requires it; the four reference notes are moved to the end and the page furniture, the standard Department of Energy disclaimer, the distribution and record-number stamps and the running page numbers are dropped. The three figures are photographs and machine drawings that are not reproduced; their captions are kept in place, and the complete report with its figures is at the source. AUTHOR AFFILIATIONS as printed: Hurst, Nash, Derzon, Kellogg, Torres, McGurn and Seaman at Sandia National Laboratories, Albuquerque, New Mexico; Jobe and Lazier at K-tech Corporation, Albuquerque. Given names are not expanded because no publisher record retrieved for this page confirms them. RELATED PAGES. What the on-axis view was built to watch: the capsule-implosion cores of the Z-pinch dynamic hohlraum at /library/stm-22f335be63 and the magnetized liner inertial fusion design for the same facility at /library/stm-57d0076dfb. Another Z diagnostic that returned an unexpected number: /library/stm-4b4aa19d9f. The wire arrays that make the pinch: /library/stm-98d874080d.

How to cite it

M. J. Hurst, T. J. Nash, M. Derzon, J. W. Kellogg, J. Torres, J. McGurn, J. Seaman, D. Jobe, S. E. Lazier (1999) Fielding of the on-axis diagnostic package at Z doi:10.1063/1.1149377

Where it sits in the curriculum

Fusion machines: pinches, focus devices and inertial drivers