Historical research guide · 0975 · 2002
Two-dimensional MHD simulations of a neon Z pinch on Hawk
J. W. Schumer · D. Mosher · B. Moosman · B. V. Weber · R. J. Commisso · Niansheng Qi · J. Schein · M. Krishnan
In one minute
A Z pinch is the most direct way there is to squeeze a plasma. Run an enormous current down a column of gas and the magnetic field that current makes pulls the column in on itself. On the Naval Research Laboratory’s Hawk generator a shell of neon is puffed through a nozzle and imploded in about 250 nanoseconds. Schumer, Mosher, Moosman, Weber and Commisso at NRL, with Qi, Schein and Krishnan of Alameda Applied Sciences, simulated that implosion in two dimensions with the MACH2 magnetohydrodynamic code and checked it against pictures of the real thing — laser shearing interferometer images that read out the electron density of the collapsing sheath shot by shot. To make the comparison honest they started the simulation from the measured gas distribution rather than an idealised one, and added neon ionisation and equation-of-state models to the code so the radiation would be computed consistently. The computed densities track the measured ones as the snowploughed channel forms and collapses.
Connection
Chapter 9 is about self-organising, self-compressing plasma structures, and the imploding pinch is the laboratory’s cleanest example of one; chapter 12 needs compression schemes whose behaviour can be predicted before the shot, and this paper is the moment a pinch simulation is held up against interferometry of the real implosion and matches.
From the source
Two-dimensional magnetohydrodynamic simulations run with the MACH2 code were benchmarked against laser shearing interferometer images of the evolving electron-density sheath during 250-nanosecond neon gas-puff Z pinch implosions on the Naval Research Laboratory Hawk generator.Abstract, sentence 1; IEEE Transactions on Plasma Science 30, 488 (2002)
The starting point of the simulation was not an idealised profile: the initial density distribution was calculated using a ballistic-flow-model fit to the measured initial gas-density distributions of the puff.Abstract, sentence 2
The implosion was modelled using an applied current profile, single-temperature energy equations and black-body-limited optically thin radiation, and for consistency with that radiation model neon ionisation and equation-of-state models were added to MACH2.Abstract, sentences 3 and 4
The computed magnetohydrodynamic ion-density distributions compare well with the interferometer images as the snowploughed plasma channel evolves during the implosion — that is, the code reproduces the measured collapse rather than merely resembling it.Abstract, sentence 5
Current-channel evolution derived from one-dimensional snowplow calculations compares well with the two-dimensional results for the same current history and initial density distribution, which indicates that axial mass flow does not strongly affect the implosion dynamics.Abstract, final sentence
What to watch: the simulations also show features that may be helpful for understanding the early and weak K-shell radiation observed near the nozzle in Double-Eagle gas-puff experiments — the measurement that would settle it is time-resolved K-shell imaging near the nozzle on a machine of that class, compared against the same modelling.Abstract, sentence 6
The way in
https://doi.org/10.1109/tps.2002.1024281How to cite it
J. W. Schumer, D. Mosher, B. Moosman, B. V. Weber, R. J. Commisso, Niansheng Qi, J. Schein, M. Krishnan (2002) Two-dimensional MHD simulations of a neon Z pinch on Hawk doi:10.1109/tps.2002.1024281