An electron beam created by a tabletop laser 2. Traditionally, direct drive has suffered from serious limitations, mainly because non-uniformities in the laser light's intensity cause the shells to implode in a less than optimal fashion. Each of the polarized beams fluctuates independently of the other, so overlapping them averages or smooths out such intensity modulations. The emission of neutrons is generally proportional to the fusion reaction rate. Maximizing the areal density is a major factor for eventually achieving self-sustaining fusion reactions with laser fusion because it increases the opportunity for alpha particles, created as a result of fusion reactions inside the shell, to deposit their energy and heat the plasma further.
Theoretical models predict additional improvements.
And for reasons not completely understood, the overall plasma rotates around the tokamak. In traditional techniques for heating the plasma with radio waves, researchers send in waves with a frequency that matches the cyclotron frequency of ions at the center of the plasma. When this resonance location was moved sufficiently far away from the center of the plasma, the overall rotation of the plasma was significantly slowed, or even reversed, and simultaneously with this change, a clear internal transport barrier developed, resulting in an extraordinary peaking of the plasma density, one that was at least two times greater than before. Internal transport barriers have been created before, but they often require the introduction of neutral atom beams which could not be feasibly placed in the designs envisioned for commercial fusion reactors. This new approach of creating internal barriers could prove to be extremely important, as it is potentially attractive for reactor applications.