Abstract
The dynamics of electrode heating, sheath flow, and contaminant plasma evolution in Sandia National Laboratories' high-power $Z$ accelerator is studied in a series of 2D relativistic particle-in-cell simulations. These dynamics can lead to the shunting of current before reaching the $Z$ pinch load, thus degrading load performance. Previous work has focused on current diverted in the upstream magnetically insulated transmission lines (MITLs) and post-hole convolute regions of $Z$. In these regions, losses were found to scale strongly with load impedance as well as the system vacuum and were calculated to be as high as 1--2 MA. Downstream from the convolute region in $Z$, current measurement is problematic, leading to a lack of understanding of the loss mechanisms in the small radius ($l3\text{ }\text{ }\mathrm{cm}$) MITL feeding the load. In this paper, we present the first ever 2D fully electromagnetic, fully kinetic simulations of plasma evolution and current shunting in the inner MITL region of $Z$. This region is defined by a radially converging MITL, which is a feature common to MA-scale $Z$ pinch accelerators. The electrodes in this region are rapidly heated via mainly Ohmic or skin depth heating. Plasmas quickly form, and surface contaminants are liberated as the temperatures exceed 700 K. Instabilities lead to a rapid plasma density fill of the inner MITL and subsequent current loss. The instability growth is likely due to the resistivity of the magnetized electrode plasma. The plasma, after exceeding ${10}^{15}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ density, leads to an additional 1--2 MA current loss in the inner MITL region.
Highlights
The Z accelerator at Sandia National Laboratories has successfully transported >25 MA current to a variety of loads
We present first-of-a-kind calculations, using the particle-in-cell (PIC) simulation code CHICAGO, which provide insight in the physical mechanisms for plasma transport and current loss in the final inner magnetically insulated transmission lines (MITLs) of the Z accelerator
A second series of shots fielded on Z that is interesting for inner MITL plasma evolution is the MagLIF 17b series
Summary
The Z accelerator at Sandia National Laboratories has successfully transported >25 MA current to a variety of loads. We present first-of-a-kind calculations, using the particle-in-cell (PIC) simulation code CHICAGO, which provide insight in the physical mechanisms for plasma transport and current loss in the final inner MITL of the Z accelerator. Understanding these processes is crucial to the design of next-generation, higher current accelerators. Downstream from the convolute post is a radially converging MITL supplying the full current to the load, which is a feature common to MA-scale Z pinch accelerators Current measurement in this region is problematic [7], leading to a lack of understanding of the loss mechanisms at a small radius (
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
