Jason Cassibry

Spherically Imploding Plasma Liners as a Standoff Driver for Magnetoinertial Fusion

Spherically imploding plasma liners formed by merging an array of high Mach number plasma jets are a proposed standoff driver for magnetoinertial fusion (MIF). This paper gives an updated concept-level overview of plasma liner MIF, including advanced notions such as standoff methods for forming and magnetizing the fuel target and liner shaping to optimize dwell time. Results from related 1-D radiation-hydrodynamic simulations of targetless plasma liner implosions are summarized along with new analysis on the efficiency of conversion of the initial liner kinetic energy to stagnation thermal energy. The plasma liner experiment (PLX), a multi-institutional collaboration led by the Los Alamos National Laboratory, plans to explore the feasibility of forming spherically imploding plasma liners via 30 merging plasma jets. In the near term, with modest pulsed power stored energy of ≲1.5 MJ, PLX is focusing on the generation of centimeter-, microsecond-, and megabar-scale plasmas for the fundamental study of high energy density laboratory plasmas. In the longer term, PLX can enable a research and development path to plasma liner MIF ultimately requiring compressing magnetized fusion fuel to ≳100 Mbar.

Estimates of confinement time and energy gain for plasma liner driven magnetoinertial fusion using an analytic self-similar converging shock model

Plasma liner driven magnetoinertial fusion (PLMIF) is a fusion energy concept that utilizes an imploding plasma liner to shock heat and compress a magnetized target plasma to fusion conditions. The fusion burn fraction is linearly proportional to the confinement (or “dwell”) time of the liner-target system at peak compression, and therefore it is important to estimate the dwell time accurately in order to assess the fusion energy yield and gain. In this work, the dwell time has been estimated using the exact solution to a self-similar converging shock model. The dwell time was found to be determined by the sum of the outgoing shock and rarefaction times through the plasma liner at peak compression, and for chosen PLMIF conditions the dwell time was on the order of 1 μs. In addition, we show that the engineering gain, i.e., the total energy extracted as electricity (from fusion plus expanded liner energy) divided by the electrical energy required to implode the liner, exceeds unity for a wide range of line...

One-dimensional radiation-hydrodynamic scaling studies of imploding spherical plasma liners

One-dimensional radiation-hydrodynamic simulations are performed to develop insight into the scaling of stagnation pressure with initial conditions of an imploding spherical plasma shell or “liner.” Simulations reveal the evolution of high-Mach-number (M), annular, spherical plasma flows during convergence, stagnation, shock formation, and disassembly, and indicate that cm- and μs-scale plasmas with peak pressures near 1 Mbar can be generated by liners with initial kinetic energy of several hundred kilo-joules. It is shown that radiation transport and thermal conduction must be included to avoid non-physical plasma temperatures at the origin which artificially limit liner convergence and, thus, the peak stagnation pressure. Scalings of the stagnated plasma lifetime (τstag) and average stagnation pressure (Pstag, the pressure at the origin, averaged over τstag) are determined by evaluating a wide range of liner initial conditions. For high-M flows, τstag ∼ ΔR/v0, where ΔR and v0 are the initial liner thick...

Two-dimensional axisymmetric magnetohydrodynamic analysis of blow-by in a coaxial plasma accelerator

When the driving magnetic pressure profile is unbalanced by the plasma density profile in a coaxial plasma accelerator, a portion of the plasma and associated current sheet may “blow by” the remaining bulk of the plasma. The fast moving plasma creates a significant back electromotive force, draining energy otherwise available for acceleration. The onset of blow-by for an unmagnetized plasma of finite length in a straight coaxial plasma accelerator was studied by exploring systematically the effects of the initial density profile, driving current, plasma temperature, inductance gradient, and electrode radii scale size on the blow-by time. In order to avoid the onset of blow-by, the principal acceleration phase needs to be less than the characteristic blow-by time, which is a function of electrode geometry, plasma conditions, and circuit parameters. For an initially uniform density profile, the total impulse at blow-by time is proportional to the current, plasma mass, jet length, and reciprocal of the elect...

Tendency of spherically imploding plasma liners formed by merging plasma jets to evolve toward spherical symmetry

We have performed three-dimensional (3D) simulations using smoothed particle hydrodynamics (SPH) in order to study the effects of discrete plasma jets on the processes of plasma liner formation, implosion on vacuum, and expansion. It was found that the pressure histories of the inner portion of the liner from 3D SPH simulations with a uniform liner and with 30 discrete plasma jets were qualitatively and quantitatively similar from peak compression through the complete stagnation of the liner. The 3D simulations with a uniform liner were first benchmarked against results from one-dimensional radiation-hydrodynamic simulations [T. J. Awe et al., Phys. Plasmas 18, 072705 (2011)]. Two-dimensional plots of the pressure field show that the discrete jet SPH case evolves towards a profile that is almost indistinguishable from the SPH case with a uniform liner, thus indicating that non-uniformities due to discrete jets are smeared out by late stages of the implosion. The processes of plasma liner formation and implosion on vacuum were shown to be robust against Rayleigh-Taylor instability growth. Finally, interparticle mixing for a liner imploding on vacuum was investigated. The mixing rate was found to be very small until after the peak compression for the 30 jet simulations.

Case and Development Path for Fusion Propulsion

This paper discusses the importance of fusion propulsion for interplanetary space travel, illustrates why the magnetoinertial fusion parameter space may facilitate the most rapid, economic path for development, justifies the choice of pulsed Z pinch, and provides a potential development path leading up to a technical readiness level 9 system. Round trips of less than one year to Mars are only possible using fusion propulsion systems. Such a system will require an onboard nuclear fission reactor for reliable startups, and so fission and fusion developments for space are mutually beneficial. The paper reviews the more than 50 year history of fusion research and summarizes results from a recent study of the fusion parameter space for terrestrial power, which suggests magnetoinertial fusion can provide the smallest, most economical approach for a fusion propulsion system. Emerging experimental data and theory show pulsed Z-pinch fusion solves some of the most deleterious instabilities and scales to fusion bre...

One-dimensional radiation-hydrodynamic simulations of imploding spherical plasma liners with detailed equation-of-state modeling

This work extends the one-dimensional radiation-hydrodynamic imploding spherical argon plasma liner simulations of Awe et al. [Phys. Plasmas 18, 072705 (2011)] by using a detailed tabular equation-of-state (EOS) model, whereas Awe et al. used a polytropic EOS model. Results using the tabular EOS model give lower stagnation pressures by a factor of 3.9–8.6 and lower peak ion temperatures compared to the polytropic EOS results. Both local thermodynamic equilibrium (LTE) and non-LTE EOS models were used in this work, giving similar results on stagnation pressure. The lower stagnation pressures using a tabular EOS model are attributed to a reduction in the liners ability to compress arising from the energy sink introduced by ionization and electron excitation, which are not accounted for in a polytropic EOS model. Variation of the plasma liner species for the same initial liner geometry, mass density, and velocity was also explored using the LTE tabular EOS model, showing that the highest stagnation pressure...

Ideal hydrodynamic scaling relations for a stagnated imploding spherical plasma liner formed by an array of merging plasma jets

This work presents scaling relations for the peak thermal pressure and stagnation time (over which peak pressure is sustained) for an imploding spherical plasma liner formed by an array of merging plasma jets. Results were derived from three-dimensional (3D) ideal hydrodynamic simulation results obtained using the smoothed particle hydrodynamics code SPHC. The 3D results were compared to equivalent one-dimensional (1D) simulation results. It is found that peak thermal pressure scales linearly with the number of jets and initial jet density and Mach number, quadratically with initial jet radius and velocity, and inversely with the initial jet length and the square of the chamber wall radius. The stagnation time scales approximately as the initial jet length divided by the initial jet velocity. Differences between the 3D and 1D results are attributed to the inclusion of thermal transport, ionization, and perfect symmetry in the 1D simulations. A subset of the results reported here formed the initial design basis for the Plasma Liner Experiment [S. C. Hsu et al., Phys. Plasmas 19, 123514 (2012)].

Status of Magnetic Nozzle and Plasma Detachment Experiment

High power plasma propulsion can move large payloads for orbit transfer, lunar missions, and beyond with large savings in fuel consumption owing to the high specific impulse. At high power, lifetime of the thruster becomes an issue. Electrodeless devices with magnetically guided plasma offer the advantage of long life since magnetic fields confine the plasma radially and keep it from impacting the material surfaces. For decades, concerns have been raised about the plasma remaining attached to the magnetic field and returning to the vehicle along the closed magnetic field lines. Recent analysis suggests that this may not be an issue if the magnetic field is properly shaped in the nozzle region and the plasma has sufficient energy density to stretch the magnetic field downstream. An experiment is being performed to test the theory regarding the MHD detachment scenario. The status of that experiment will be discussed in this paper.

Scale coupling in Richtmyer-Meshkov flows induced by strong shocks

We perform the first systematic study of the nonlinear evolution and scale coupling in Richtmyer-Meshkov (RM) flows induced by strong shocks. The smoothed particle hydrodynamics code (SPHC) is employed to ensure accurate shock capturing, interface tracking and accounting for the dissipation processes. We find that in strong-shock-driven RMI the background motion is supersonic. The amplitude of the initial perturbation strongly influences the flow evolution and the interfacial mixing that can be sub-sonic or supersonic. At late times the flow remains laminar rather than turbulent, and RM bubbles flatten and decelerate. In the fluid bulk, reverse cumulative jets appear and “hot spots” are formed—local heterogeneous microstructures with temperature substantially higher than that in the ambient. Our numerical simulations agree with the zero-order, linear, weakly nonlinear, and highly nonlinear theoretical analyses as well as with the experiments and suggest that the evolution of RMI is a multi-scale and heter...