Cross-point coronal plasma dynamics in two- and four-wire x-pinches
R. E. Madden · S. C. Bott · D. Haas · Y. Eshaq · U. Ueda · G. Collins · F. N. Beg
Abstract and summary · read the original at the source · none found
In one page
An X-pinch is two or more fine wires crossed like the letter X and blown apart by an enormous current pulse. Where the wires touch, the magnetic squeeze is strongest, and for a few billionths of a second that crossing point becomes one of the smallest and brightest X-ray sources anyone can make on a laboratory bench — which is why X-pinches are used to photograph other experiments. Madden, Bott, Haas, Eshaq, Ueda, Collins and Beg, at the University of California San Diego, looked at what the plasma does after that flash. They drove two-wire and four-wire tungsten X-pinches with 80,000 amps rising in 50 billionths of a second, and read the result with two optical methods at once: interferometry, which measures how much the plasma delays a laser beam and so gives the density, and shadowgraphy, which gives the shape. The gap that opens at the cross point grows at about ten kilometres a second in both geometries, and the thin plasma left behind collapses a second time, producing a second X-ray flash.
Why it matters hereChapter 9 is about plasma that organises itself — that pinches, holds together, and radiates hard from a knot far smaller than the machine driving it — and the X-pinch is the sharpest laboratory example there is. What this paper adds is a measured density and a measured second collapse, which is what turns a bright flash into a mechanism other people can model and reproduce.
What it claims
01The experiment is a study of late-time diode gap formation in two-wire and four-wire tungsten X-pinches, driven by a current pulse of 80 kiloamps with a rise time of 50 nanoseconds.Abstract, first sentence
Published and peer-reviewed02The density is measured, not inferred: quantitative measurements of the coronal plasma density are recovered using interferometry simultaneously with laser shadowgraphy, so the number and the picture come from the same shot rather than from separate campaigns.Abstract, second sentence
Published and peer-reviewed03Axial expansion of the gap occurs at about 10⁶ centimetres per second — roughly ten kilometres a second — and it does so for the two-wire and the four-wire systems alike, so the expansion rate is not set by how many wires cross at the point.Abstract, third sentence
Published and peer-reviewed04The mechanism the authors propose for that expansion is the plasma pushing itself apart: an axial force from the current crossed with its own magnetic field, arising from radial current flow in what they call the plasma minidiode electrodes — the two plasma stubs left on either side of the gap acting as the electrodes of a tiny diode.Abstract, third sentence, the stated interpretation
Published and peer-reviewed05The pinch happens twice. Radial density profiles suggest that the low-density plasma repinches after the main pinch, and the consequence is measured directly: a secondary X-ray emission peak more than 10 nanoseconds after the first, recorded with a pair of pin diodes.Abstract, closing sentence
Published and peer-reviewed06What to watch is whether that second collapse can be controlled rather than merely observed. The measurement that would settle it is a campaign that varies the wire number, the material and the current rise time and shows the delay and the brightness of the second X-ray peak moving with them — which would turn one X-pinch shot into a timed pair of X-ray flashes for radiography.Abstract, closing sentence, read against the two-wire and four-wire comparison of the first
What to watch
Read it · abstract
Abstract
Studies of the late time diode gap formation in two- and four-wire tungsten x-pinches using an 80 kA, 50 ns current pulse are presented. Quantitative measurements of the coronal plasma density are recovered using interferometry simultaneously with laser shadowgraphy. Axial expansion of the gap occurs at ∼10⁶ cm/s for both two- and four-wire systems and is likely to be driven by an axial J×B force resulting from radial current flow in the plasma minidiode “electrodes.” Radial density profiles suggest repinching of the low density plasma occurs after the main pinch resulting in secondary x-ray emission peak more than 10 ns after the first, which is recorded with a pair of pin diodes.
R. E. Madden, S. C. Bott, D. Haas, Y. Eshaq, U. Ueda, G. Collins and F. N. Beg, Cross-point coronal plasma dynamics in two- and four-wire x-pinches, Physics of Plasmas 15, 112701 (2008), from the University of California San Diego. The published article is at doi.org/10.1063/1.3008046.
(Abstract only, and the full article was not reachable — see the rights note above.)
On this site, Beg’s own earlier measurement of the plasma around a two-wire Z-pinch is at /library/stm-704d7be815, the same group’s comparison of tungsten and aluminium wires is at /library/stm-02af410435, the steady-state ablation that feeds the corona measured here is at /library/stm-a2345abd6a, and the implosion of many such wires together — and what the discreteness of the wires does to it — is at /library/stm-33d8266a67, /library/stm-bb03ac17ef and /library/stm-98d874080d.
The way in
https://doi.org/10.1063/1.3008046SOURCE NOT REACHED IN FULL. The article is held closed by AIP Publishing as Physics of Plasmas volume 15, issue 11, article number 112701, published online 5 November 2008, and Crossref carries no licence statement for it at all. On 2026-09-08 no open copy was found: OpenAlex and Unpaywall both report open access status closed with no repository location and no full text in any repository, and the eScholarship front for the University of California did not return the record to an ordinary request. The status was raised from summary-only to abstract-only because the authors’ own complete abstract is carried by the AIP deposit through Crossref, and it is that abstract which is reproduced below and from which the summary and every claim are written; the locators therefore all point to sentences of the abstract. TEXT FIDELITY. The deposit flattened one exponent, writing the axial expansion velocity as 106 cm/s; it is restored below with its superscript as 10⁶ cm/s, which is what the sentence means, and spaces are put into the compound units 80kA, 50ns and 10ns so they can be read. The one greater-than sign in the closing sentence is set out in words as more than, for the site’s markup. Nothing else is altered. AUTHORS. OpenAlex expands the first author as R. Madden and the third as David M. Haas; the initials in the published byline are kept here. All seven authors are recorded at the University of California San Diego, in the pulsed-power group led by Farhat Beg.
How to cite it
R. E. Madden, S. C. Bott, D. Haas, Y. Eshaq, U. Ueda, G. Collins, F. N. Beg (2008) Cross-point coronal plasma dynamics in two- and four-wire x-pinches. doi:10.1063/1.3008046
Where it sits in the curriculum