Magnetized Target Fusion

MTF is a fusion approach that is in between magnetized fusion (MF) and inertial confinement (ICF). In MF the plasma density is very low (10¹⁴ particles/cm³) so the fusion rate is slow and the plasma must be contained for many seconds in order to make more energy than initially invested in heating the plasma. This is hard because the very hot plasma tends to twist and escape the magnetic field. In ICF the plasma density is 1000 times the density of a solid (10²⁵ particles/cm³). The reaction rate is enormous and the fusion energy is released in ~1 nanosecond. That is faster than the time for the plasma to cool down even if there is no attempt at preventing the heat from escaping. The problem here is that a lot of energy must be crammed in a very small spot, and in a very short time to achieve these conditions. The energy driver to do that (laser, particle beam) is difficult.

In MTF a relatively cold plasma with an embedded electrical current is generated inside a conductive cavity. The electric current produces a magnetic field that helps confining the plasma in a similar way to MF. The cavity is then rapidly collapsed like in ICF. Because the magnetic field cannot penetrate the conductive wall, the plasma is compressed and heated to thermonuclear conditions. Because of the magnetic field the heat does not escape as fast as ICF so the compression can be slower and the peak density can be less (~10²⁰ particles/cm³). Yet this density is one million times more than MF so the magnetic configuration must keep the heat for only 1 microsecond; a much easier task than MF. The slower rate of compression and larger plasma considerably relax the peak power and focus of the energy driver allowing a simpler, cheaper system to be used.

Los Alamos National Lab in the US is working on MTF. In their approach, the cavity is a metal tube and it is collapsed by passing a large electrical current in it. The current reacts with the induced magnetic field to produce a force that crushes the tube. (http://wsx.lanl.gov/mtf.html)
 
A great source of documentation on LANL's approach is located here: http://wsx.lanl.gov/frxl-pubs.html
 
More information about MTF can also be found on the Wikipedia page, Magentized target fusion.