Andrea Schmidt (15-ERD-034)
Compact high-flux, reusable neutron sources that operate in deuterium fuel are of interest to a variety of fundamental research areas in radiation detection, nuclear physics, astrophysical processes, and Inertial Confinement Fusion. Miniature dense-plasma focus Z-pinch devices could fill this need if their yield was increased and their pulse is lengthened. The name refers to the direction of the current in these devices, the Z-axis on a normal three-dimensional graph. The device is a plasma-confinement system consisting of two coaxially located electrodes with a high-voltage source at one end. In the presence of a low-pressure gas, the high-voltage source induces a plasma sheath formation. The plasma sheath is pushed down the length of the electrode, collapses, and implodes, creating a high-density pinch effect that emits high-energy electron and ion beams, x rays, and neutrons in the presence of deuterium. In this project, we plan to use a unique Livermore simulation tool to better understand the kinetic instabilities in these plasmas that drive the ion beam formation and neutron yield. Through simulations, we will gain an understanding of how different driver properties affect the formation of these instabilities, and will perform the first three-dimensional kinetic dense-plasma focus calculations. We will apply this new understanding to increase yield in a miniature dense-plasma focus device with stockpile stewardship applications in mind.
If this project is successful, we will pursue building a prototype, compact dense-plasma focus device using static-gas-fill deuterium that achieves relevant yields for stockpile stewardship applications. Such a compact, short-pulse neutron source could also have relevance for portable active interrogation relevant to nonproliferation and nuclear terrorism. We are leveraging the modeling capabilities developed at Lawrence Livermore to identify parameters for the kinetic instabilities that create large-beam-forming gradients, a fundamental science problem that remains unsolved after 40 years of Z-pinch research. An understanding of these instabilities and the conditions under which they arise would allow us to control and tailor the behavior of dense-plasma focus systems. We expect to characterize and optimize the neutron pulse shape to lengthen the neutron pulse with our device. The approach will be to purposefully induce multiple pinches. Additionally, the presence of a solid target will lengthen each pinch's neutron pulse by about 70 ns because of time-of-flight considerations for a target that is 5 cm from the pinch. We will use a scintillator in current mode for this measurement. In addition, we will introduce the first three-dimensional fully kinetic modeling of a dense-plasma focus system.
This project enhances capabilities in fully kinetic Z-pinch modeling, a component of the Laboratory's high-energy-density science core competency. Our work also enables applications in the strategic focus area of stockpile stewardship science in which the predictive capability for nuclear weapon performance requires fundamental understanding of extreme, high-energy-density states of matter. In addition, creating a path to portable neutron sources to be used for active radiation interrogation would enable key applications for nuclear threat reduction, and is relevant to the core competency in nuclear, chemical, and isotopic science and technology.
FY16 Accomplishments and Results
In FY16 we (1) completed design of a new miniature dense-plasma focus machine including engineering drawings, (2) held a preliminary design review followed by a final design review; (3) constructed the dense plasma focus device; and (4) achieved first plasmas (see figure).
Publications and Presentations
- Cooper, C. M., et al., Construction of a compact, low-inductance, 100 J dense plasma focus for yield optimization studies. American Physical Society Division of Plasma Physics Annual Meeting, San Jose, CA, Oct. 31–Nov. 4, 2016. LLNL-ABS-697275.
- Jiang, S., et al., Study on the polarity riddle of the dense plasma focus. 58th American Physical Society Division Division of Plasma Physics Annual Meeting, San Jose, CA, Oct. 31–Nov. 4, 2016. LLNL-ABS-697681.
- Liu, J. X., Seeding the m=0 instability in dense plasma focus z pinches. American Physical Society Division Division of Plasma Physics Annual Meeting, San Jose, CA, Oct. 31–Nov. 4, 2016. LLNL-ABS-697806.
- McMahon, M., et al., Optimizing dense plasma focus neutron yields with fast gas puffs. American Physical Society Division Division of Plasma Physics Annual Meeting, San Jose, CA, Oct. 31–Nov. 4, 2016. LLNL-ABS-697538.
- Povilus, A., et al., Preionization techniques in a kJ-scale dense plasma focus. American Physical Society Division Division of Plasma Physics Annual Meeting, San Jose, CA, Oct. 31–Nov. 4, 2016. LLNL-ABS-697764.
- Schmidt, A., et al., Optimization of intense dpf z-pinch neutron source via experiments and kinetic modeling. Hardened Electronics And Radiation Technology Technical Information Meeting, Apr. 24–28, Denver. LLNL-ABS-677487.
- Sears, J., et al., The Effect of driver rise-time on pinch current and its affect on plasma focus performance and neutron yield. American Physical Society Division of Plasma Physics Annual Meeting, San Jose, CA, Oct. 31–Nov. 4, 2016. LLNL-ABS-697680.