Session BM9: Mini-Conference on Magneto-inertial Fusion Science and Technology I

Spherically Imploding Plasma Liners as a Standoff Magneto-Inertial-Fusion Driver

Spherically imploding plasma liners formed by merging hypersonic plasma jets are a proposed compression driver for magneto-inertial fusion (MIF).  Under the ARPA-E ALPHA program, the Plasma Liner Experiment--ALPHA (PLX-$\alpha$) plans to culminate in forming spherically imploding sub-fusion-scale plasma liners [1] via 36 merging hypersonic plasma jets (with initial $n_i \sim 2\times 10^{16}$~cm$^{-3}$, $v_{\rm jet} \approx$ 50~km/s, mass $\sim 1$~mg, and various gas species).  We summarize experimental results on the formation of a conical section of spherically imploding plasma liners by merging six [2] and seven plasma jets.  Data from fast-framing-cameras, visible spectrometers, and a multi-chord interferometer have been analyzed to assess (i) ion heating (and associated liner-Mach-number degradation) due to collisional shock formation between merging jets [3], and (ii) liner uniformity upon jet merging.  These data are benchmarking code calculations, which will set requirements on fusion-scale plasma liners.  [1] S. C. Hsu and Y. C. F. Thio, J. Fusion Energ.~{\bf 37}, 103 (2018); [2] S. C. Hsu et al., {\em IEEE Trans.\ Plasma Sci.}~{\bf 46}, 1951 (2018); [3] S. J. Langendorf et al., submitted (2018); https://arxiv.org/abs/1805.09933.   

Coaxial Plasma Gun Development for Plasma-Jet-Driven Magneto-Inertial Fusion (PJMIF)

PJMIF requires high-Z (e.g. Xe) plasma jets with velocity above 50 km/s, particle density > 10¹⁷ per cc, Mach number > 15, jet length < 5 cm, jet- to-jet variations in mass of less than 5% and launch time of less than 200 ns, with high degree of density and velocity uniformity within the jet. The deflagration and snow-plow acceleration of plasma tend to produce long jets. The plasma may be accelerated in the slab mode, with suitably contoured electrodes to avoid the blow-by instability. The plasma gun has undergone two generations of development. Development of a third generation of the gun (HJ1) is underway to meet the needs of PLX-a, an experiment to form a spherical plasma liner. The major components of the gun are the capacitor module, the PFN, the gun electrodes, the gas valve, the switch, and the pre-ionizer. Highlights of the development and the test data for these various components and the integrated system will be presented and dis­cussed. 
  

Sheared-flow Stabilized Z-Pinch Reactor Embodiment

The sheared-flow stabilized (SFS) Z-pinch has demonstrated long-length and long-lived Z-pinches with T_i ~ 1-2 keV, n_e > 10^23 m^-3, for 100s of MHD instability growth times.  The fusion Z-pinch experiment, FuZE, has shown neutron production over periods of 5-8 us when operated with a 20% D/80% H or He mixture.  Yield calculations are >10^5 neutrons per pulse, agreeing with cross-section estimates and scaling as the square of the D concentration.  Reactor embodiment for the SFS Z-pinch reactor consists of a vertically-oriented pinch in a cavity formed by Li-Pb flowing over a weir wall.  Li-Pb serves as the Z-pinch outer electrode, heat transfer material, tritium breeding blanket, and biological shield.  MCNP is used to calculate neutron transport, including the tritium breeding ratio (TBR).  Configurations have been found reaching the goal of TBR > 1.1 with the 17% Li/83% Pb eutectic and natural Li-6 enrichment of 7.5%.  A model is under development to calculate the time required to build up tritium inventory when starting with D-D operation.  Bred tritium is introduced into the deuterium fuel stock, increasing the net TBR, bootstrapping the reactor to 50% D / 50% T.  SFS Z-pinch background, results, and reactor embodiment studies will be presented.   

Development of multi-beam ion accelerators for plasma heating

Reducing the size, power needs and cost of accelerators opens new opportunities in mass spectrometry, ion implantation and ultimately plasma heating for fusion. We have demonstrated a compact multi-beam RF accelerator [1] with ion acceleration in an array of 3x3 beams. Our technology is based on wafer-based components (silicon or circuit boards) where beam transport is in the direction of the surface normal to the wafer. This allows stacking of wafers to increase beam energy while limiting the peak voltage to several kilovolts.  The wafer-based implementation allows us to operate multiple ions beams on a single wafer in parallel for much increased current densities per wafer in a multi-beamlet arrangement compared to a single beam with one large aperture. We report on the integration of all accelerator components (matching section, focusing elements and acceleration stages) and will discuss paths for scaling to high beam power for applications in manufacturing, materials analysis and fusion plasma heating. 
[1] Persaud, A. et al., Rev. Sci. Instrum. 88, 063304 (2017); Seidl, P. A. et al. , Rev. Sci. Instrum. 89, 053302 (2018).