Inertial Fusion Energy

In inertial fusion energy (IFE), a "driver" focuses beams of accelerated ions or intense laser light on a "target" filled with hydrogen fuel. An IFE power plant would have separate areas for the driver, a factory for making the targets, a target chamber where the fusion reactions occur, and a steam turbine to generate electricity. This separability provides design flexibility and allows the driver and target factory to be protected from the fusion radiation environment. The driver must ignite several fusion targets per second to produce the desired power level in the chamber. A single driver could be used to operate multiple chambers by switching the final beam paths between chambers. Various driver concepts are being studied, some for both energy and defense purposes.





HEAVY-ION DRIVER
Because of the need for electrical efficiency and for rapidly repeated firings, one leading approach is to use beams of heavy ions, from either a linear or a circular accelerator. This illus- tration shows proof-of-principle configuration for a new type of circular accelerator for very-high- beam currents. 









                   Other IFE Driver Concepts

DIODE-PUMPED SOLID-STATE
LASER DRIVER
Using diodes instead of flashlamps to pump a solid-state laser could permit the rapidly repeated firings and efficiency necessary for power generation. The laser diode array shown was developed at Lawrence Livermore National Laboratory.






KRYPTON-FLUORIDE GAS LASER DRIVER
With the KrF laser, the laser medium is a gas that can be circulated for heat removal in high pulse- repetition-rate applications such as IFE. Target physics experiments are being conducted at the Naval Research Laboratory using the Nike KrF laser. Shown here are the large black magnetic field coils used to guide electron beams through the KrF amplifier cell.


LIGHT-ION DRIVER
Light-ion accelerators are dominated by the pulsed-power hardware used to produce high currents of light ions such as lithium. Conceptual designs of IFE power plants using light-ion drivers have been completed by the University of Wisconsin and Sandia National Laboratories, New Mexico.


HOW INERTIAL FUSION WORKS






                  IFE Target Research


In IFE, the fusion reactions occur within a small capsule containing the deuterium- tritium (DT) fuel, and each driver concept requires specific targets and related mechanisms. In "indirect drive" targets, the laser or ion beams do not strike the target capsule directly but enter a metal cylinder and create thermal x-rays when their energy strikes the cylinder walls; it is the x-rays that heat the surface of the fusion capsule. With "direct drive" targets, the beams are focused directly on the target capsule.

TARGETS FOR SOLID-STATE LASER
In the indirect target at left, the outer metal cylinder of gold or lead contains a plastic fusion cap- sule (about 3 mm in diameter) that is lined with a solid layer of fuel and that holds a small amount of DT gas. Laser beams enter the cylinder in two conical arrays. Capsules A direct drive target is shown below.

TARGET FOR HEAVY-ION DRIVER
In the heavy-ion target, the plastic fuel capsule is completely surrounded by materials that first convert the ion energy into x rays and then contain the x rays in the volume surrounding the capsule.



TARGET PHYSICS RESEARCH AT NIF
The National Ignition Facility will prove inertial ignition and energy "gain" -that is, more energy will be released than is required to cause the fusion reactions. Research performed on the NIF will also greatly advance knowledge about the physics of fusion targets for energy production.


MAGNETIC FAST-IGNITION TARGETS
Computer modeling at Lawrence Livermore National Laboratory indicates that an emplaced magnetic field within an inertial-fusion fuel cap- sule can drive a "hot-spot ignition burn" with only modest compression.