  Magneto-Inertial Fusion Technology Inc. has been working on a Z-pinch concept
where a high atomic number liner is compressing a fusion fuel
(deuterium-deuterium, or deuterium-tritium) target. The viability of this so
called Staged Z-pinch (SZP) concept as a potential high-gain fusion energy
source has been questioned in a recent publication by Lindemuth et al [1]. The
authors attempted to reproduce previously published MACH2 simulation results
[2-4] for Z-machine parameters using three different MHD codes: Hydra, Raven
and MHRDR. Their conclusion was that "there is no conceivable modification of
the parameters that would lead to high-gain fusion conditions using these other
codes". Although they used well established MHD codes to check the SZP concept,
and correct input current profiles, we show that their Lagrangian formalism was
likely not treating the vacuum/liner boundary properly. Proper modeling using
Lagrangian, Eulerian or Adaptive Lagrangian-Eulerian (ALE) formalism indeed
confirms that fusion energy production > 1 MJ can be expected without alpha
heating, and significantly higher if alpha heating is included. It is shown
that magnetosonic shocks play an important role in preheating the target plasma
and in piling liner mass at the liner/target interface, which substantially
increases the ram pressure just before the pinch stagnation time.
