Ultrafast x-ray imaging of pulsed plasmas in water

Letter
Open Access

Ultrafast x-ray imaging of pulsed plasmas in water

Christopher Campbell, Xin Tang, Yancey Sechrest, Kamel Fezzaa, Zhehui Wang, and David Staack

Phys. Rev. Research 3, L022021 – Published 8 June 2021

Abstract

Ultrafast x-ray imaging is useful for diagnosing a wide range of nanosecond-time scale physical processes, particularly those concealed by optical emission or otherwise opaque objects. Here we use the ultrafast x-ray imaging facilities at Argonne National Laboratory's Advanced Photon Source to interrogate nanosecond-pulsed single-electrode plasma initiation processes in water ( $+ 25$ kV, 10 ns, 5 mJ), with supporting nanosecond optical imaging and x-ray diffraction computational model. These results clearly resolve narrow ( $\sim 10 μ m$ ) low-density plasma channels during initiation time scales typically obscured by optical emission. This multiphase environment is not well described in literature, and these experimental results appear to be inconsistent with prevailing breakdown initiation hypotheses. This work also proposes this plasma process as a cheap, compact, and repeatable benchmark imaging target with hypersonic phenomena (29.1 km/s) and very high-power densities ( $1 TW / {cm}^{2}$ ), useful for the development of next-generation ultrafast imaging of inertial confinement fusion and other nanosecond processes of interest.

Received 12 February 2020
Revised 15 July 2020
Accepted 15 March 2021

DOI:https://doi.org/10.1103/PhysRevResearch.3.L022021

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Glow & corona plasma discharges Nonlinear phenomena in plasmas Plasma discharges Plasma discharges in liquid & solid Plasma interactions Plasma sources Shock waves & discontinuities in plasma

Laboratory plasma Low-temperature plasma

Optical plasma measurements Plasma diagnostic techniques X-ray & gamma ray plasma measurements

Plasma PhysicsAccelerators & Beams

Authors & Affiliations

Christopher Campbell ¹, Xin Tang ¹, Yancey Sechrest ², Kamel Fezzaa ³, Zhehui Wang ^2,*, and David Staack^1,†

¹Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843, USA
²Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
³X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

^*zwang@lanl.gov
^†dstaack@tamu.edu

Article Text

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Supplemental Material

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References

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Issue

Vol. 3, Iss. 2 — June - August 2021

Subject Areas

Plasma Physics

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Images

Figure 1
The pulsed water plasma of interest to this work imaged with four different methods, in order of decreasing exposure time: (a) 67 ms, (b) $2.38 μ s$ , (c) 10 ns, and (d) 50 ps.
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Figure 2
(a) Diagram of the laser-triggered driving circuit with (b) voltage and current traces for a typical event. (c) Power and energy calculated from direct integration. $R_{1} = 20 M Ω, C_{1} = 1 nF$ , and $V_{b} = + 25 kV$ . During this event a total of 242 mJ was dissipated: 225 mJ ( $93 %$ ) was dissipated by the air spark switch, 5 mJ ( $2 %$ ) contributed to plasma generation, and the remaining 12 mJ ( $5 %$ ) was lost via long-time scale heating and electrolysis. The resulting plasma current pulse had a FWHM of 12 ns and a peak of 23 A.
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Figure 3
A series of video frames from high-speed (2.38 $μ s / frame$ ) backlit photography of a single water discharge event {(a), Supplemental Video S1 [25]}. Collection of backlit fast-exposure (10 ns) ICCD images from many disparate events, sorted by camera delay relative to time of event as measured by peak PMT signal, with $t = 0$ defined to be the average time of peak current {(b), Supplemental Video S2 [25])}. Images from (b) were used to generate plots of plasma channel length (c) and average frame brightness (d) vs time.
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Figure 4
Frames from ultrafast x-ray imaging videos of two pulsed water plasma events [(a) and (b)], with time stamps annotated relative to peak plasma current as measured through the positive electrode. Frame rates are 136 kfps (a) and 272 kfps (b), or 7.37 and 3.69 $μ s / frame$ respectively. Resolution is 2 $μ m / pixel$ . Note the evolution from predischarge to small-diameter long plasma channels to large-diameter cavitation and expansion, as emphasized in (c) and (d) with two-frame composite images from (a) and (b), respectively. See Supplemental Material, Sec. 2 [25] for additional multiframe videos of single events, all of which show correlation in position between the small-diameter channels and larger-diameter bubbles. The event shown in (a) corresponds to Supplemental Video S3 [25].
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Figure 5
(a) Illustration of a typical plasma channel cutline interpolation from an x-ray image; (b) typical diffraction model result after optimization relative to the average experimental cutline. Dotted lines represent first and third quartiles of the cutline distribution for each lateral position. For this particular result, the channel diameter and specific gravity were found to be $11 . 7_{- 1.3}^{+ 1.5} μ m$ and $0 . 09_{- 0.09}^{+ 0.17}$ , respectively. Computational results for 27 interpolated experimental cutlines are summarized in (c) $d_{channel}$ vs $t$ and (d) $S G_{vap}$ vs. $t$ plots, with time measured relative to water plasma initiation. See Supplemental Figure S9 [25] for a discussion on uncertainty in these plots. Note the general trend that longer times after initiation correlate with larger-diameter plasma channels and lower specific gravities on time scales much faster than the x-ray frame rate. Also included in Fig. 5 are the maximum plasma channel lengths (red crosses) taken from each event, the fastest of which implies a channel propagation speed of 11.7 km/s.
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