Historical research guide · 1049 · 2013

Z-Pinch fusion-based nuclear propulsion

Janie H. Miernik · Geoffrey Statham · Leo Fabisinski · C. Dauphne Maples · Robert B. Adams · Tara Polsgrove · Sharon Fincher · Jason Cassibry · Ross J. Cortez · Matt Turner · Thomas K. Percy

In one minute

NASA Marshall’s 2010 study turns a Z-pinch fusion pulse into a spacecraft-engine concept. A roughly 100-megaampere current passes through deuterium-tritium fuel for microseconds; its magnetic field compresses the plasma. The concept fires ten times per second. Eight superconducting ring assemblies form a parabolic magnetic nozzle around the fusion point. They keep the expanding plasma away from material walls and transfer its reaction force to the vehicle through magnetic pressure. A lithium-6 liner returns current, absorbs some neutrons, and is intended to breed tritium. The study’s design point is 19,436 seconds of specific impulse and about 38 kilonewtons at 10 hertz. Those are model outputs for a proposed system; the paper specifies component tests, not a flight-engine result.

Connection

The paper connects a pinched plasma column to engineering choices: ring layout, capacitor energy, radiation protection, materials, and structural loads. It gives the reader a propulsion system that can be tested one subsystem at a time.

From the source

Recent advances in experiment and theory show favourable scaling of fusion power output yield as the fourth power of the drive current, I⁴, in the Z-Pinch dense plasma focus.Abstract and Introduction, citing Velikovich et al., Z-Pinch plasma neutron sources, Physics of Plasmas 14, 022701 (2007)
The design point is a specific impulse of 19,436 seconds and a useful impulse to the vehicle of 3812 newton-seconds per pulse, or about 38 kilonewtons of thrust at the 10 hertz pulse rate — a fortyfold increase in specific impulse over chemical propulsion. The assumptions behind it are 100 milligrams of deuterium-tritium fuel per pulse, a compression ratio of 10, an ignition temperature of 20 kiloelectronvolts, and an expanding plasma of 0.02 kilograms carrying 1 × 10⁹ joules of initial kinetic energy.Section 2, Main engine propulsion concept; Table I; Conclusion
The nozzle is magnetic, not material. Eight ring assemblies form a parabola with the fusion point at its focus; each ring carries a yttrium-barium-copper-oxide superconductor with a transition temperature of 92 kelvin held at 77 kelvin by liquid nitrogen, which lays down the seed field, plus a separate thrust coil. The expanding plasma shell compresses that field, the rising magnetic pressure keeps the plasma off the rings, and the field springs back — transferring the pulse to the vehicle without contact.Section 2, Main engine propulsion concept
The lithium-6 liner does three jobs in one part. It is injected through an annular nozzle so that it meets the deuterium-tritium fuel at the cathode point and serves as the current return path that completes the circuit; it acts as a neutron getter and radiation shield; and the reaction between neutrons and lithium-6 breeds tritium, adding fuel back into the reaction and boosting the energy output.Introduction and Section 1, Z-Pinch fusion reaction modelling
The engine recharges itself between shots. The thermodynamic model estimates a Z-Pinch gain of 3, so a pulse releasing 1 gigajoule needs 333 megajoules delivered into the fuel in 100 nanoseconds; at 80 percent capacitor charge efficiency the bank must hold 416 × 10⁶ joules. Eight Marx-generator stages ringing the pinch charge in parallel over microseconds and discharge in series in nanoseconds, and the current induced in the thrust coils during each plasma expansion recharges them.Section 3, Z-Pinch energy regeneration and discharge system
The NASA presentation rates high-temperature Z-Pinch and intense electrical pulse power at technology readiness level 4, magnetohydrodynamic electricity at 5, thermonuclear equations of state and dynamic plasma radiation shielding at 3, and advanced structures and reaction containment at 2. A nozzle-coil assembly that survives repeated pulses is the hardware test that joins those parts into an engine.Key technology maturity chart, NASA presentation NTRS 20120016678

The way in

https://doi.org/10.1016/j.actaastro.2012.02.012

Historical source-access record. This guide links to the original; it does not reproduce the paper text.

WHAT IS REPRODUCED. The Elsevier journal article at the DOI above is closed and is NOT the text on this page. The text below is the NASA Marshall Space Flight Center conference version of the same study by the same team — Z-Pinch Magneto-Inertial Fusion Propulsion Engine Design Concept, presented at the Seventh IAA Symposium on Realistic Near-Term Advanced Scientific Space Missions, Aosta, Italy, 11 to 14 July 2011 — read in full from the NASA Technical Reports Server, record 20120016553, file 20120016553.pdf. As a work of the United States Government prepared at Marshall Space Flight Center it carries no copyright. A second NASA record, 20120016678, is the presentation Janie Miernik gave at the same symposium; it was also read in full and supplies the technology-readiness figures and the vehicle mass statement quoted in the claims, and each of those locators names it. REPAIRS MADE TO THE EXTRACTED TEXT AND NOTHING ELSE: superscripts lost by the PDF text layer are restored — the current scaling reads I⁴, the pulse timescale reads 10⁻⁶ seconds, the capacitor bank energy reads 416 × 10⁶ J and the pulse kinetic energy reads 1 × 10⁹ joules; reaction arrows dropped by the extractor are restored; running heads, page numbers, figure images and figure captions are dropped as page furniture; and three broken word joins are closed — Z-Pinch Magneto in the title, utilized a, and 30-day. AUTHOR NAMES. Crossref carries this author list with initials only; the given names here are read from the NASA cover pages of the two records above.

How to cite it

Janie H. Miernik, Geoffrey Statham, Leo Fabisinski, C. Dauphne Maples, Robert B. Adams, Tara Polsgrove, Sharon Fincher, Jason Cassibry, Ross J. Cortez, Matt Turner, Thomas K. Percy (2013) Z-Pinch fusion-based nuclear propulsion doi:10.1016/j.actaastro.2012.02.012

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