Two approaches to controlled thermonuclear fusion have dominated the research landscape for decades – magnetic confinement fusion, which uses large, externally generated magnetic fields to confine a large, sparse plasma over long timescales, and inertial confinement fusion, which uses intense radiation fields (lasers or X-rays) to implode capsules of fuel, transiently creating powerful fusion explosions.

A third approach, magnetized target fusion (MTF, also called magneto-inertial fusion) utilises aspects of both of these techniques. A magnetised plasma target is formed and then compressed inside a “liner”, which can be made from imploding, heavy plasma, or a solid metal wall. The magnetic fields insulate the target from the cold liner, keeping the fuel hot as it sub-sonically compresses to a hot, dense state where fusion occurs. There has recent been growing enthusiasm for this approach from the private sector, with start ups such as Fuse and Pacific Fusion planning large pulsed-power facilities to test MTF concepts.

An outstanding challenge in MTF is understanding how heat is transported in these hot, dense, magnetized plasmas. Exotic effects outside of standard magnetohydrodynamics, such as the Nernst term, can lead to rapid destruction of the insulating magnetic fields. Tangled magnetic field lines, generated by turbulence can provide very long connection lengths for plasma, effectively lower the bulk conductivity. Using PUFFIN we will create and sustain MTF-relevant plasmas and study heat transport effects within them to assess the viability of various MTF approaches.

Another challenge in MTF is the magneto-hydrodynamic stability of the imploding plasma. The long time scale of PUFFIN makes it ideal for studying the growth of instabilities such as the Rayleigh Taylor and Kelvin Helmholtz, and also for studying techniques to mitigate these instabilities, such as density-profile tailoring and shear-flow stabilisation.

Further Reading