Magnetized Target Fusion - MTF Approach

MTF Approach

While MCF and ICF attack the Lawson criterion problem from different directions, MTF attempts to work between the two. Magnetic fusion confines a dilute plasma at about 10 cm. Inertial fusion works around 10 cm. MTF aims for 10 cm. At this density, the fusion rate is relatively slow, so some confinement time is needed to allow fuel to undergo fusion. Here too, MTF works between the ~1 second times of magnetic methods, and the nanosecond times of inertial, aiming for times on the order of 1 µs. In MTF, magnetic fields are used to slow down plasma losses, and inertial compression is used to heat the plasma.

In general terms, MTF is an inertial method. The density is increased through a pulsed operation that compresses the fuel, and since temperature is the average energy per unit density, as long as heat is not lost to the surroundings, the temperature of the fuel is raised by a similar amount. In traditional ICF, more energy is added through the lasers that compress the target, energy that leaks away through a variety of processes. No more energy is added in MTF. Instead, a magnetic field is created before compression that confines fuel, and insulates it so less energy is lost to the outside. The result, compared to ICF, is a somewhat-dense, somewhat-hot fuel mass that undergoes fusion at a medium reaction rate, so it only must be confined for a medium length of time.

At first glance it might seem that this approach would have no advantages over traditional ICF methods. All that has changed is a tradeoff between confinement time and density, but the end result is the same. The reason MTF appears to be so much more practical is that the lower density it needs can be formed through a variety of processes that are relatively efficient and inexpensive, whereas ICF demands specialized high-performance lasers of low efficiency. The cost and complexity of these lasers, termed "drivers", is so great that traditional ICF methods appear to be impractical for commercial energy production. Likewise, although MTF needs magnetic confinement to stabilize and insulate the fuel while it is being compressed, the needed confinement time is thousands of times less than for MCF. Confinement times of the order needed for MTF were demonstrated in MCF experiments years ago.

This is the promise of the MTF approach. Making a pure MCF or ICF device needs extremely high-end engineering that is still being experimented on, with no guarantee that it will ever be practical. But the densities, temperatures and confinement times needed by MTF are well within the current state of the art and have been repeatedly demonstrated in a wide variety of experiments. LANL has referred to the concept as a "low cost path to fusion".