Magnetic Mirror

A magnetic mirror, also called a magnetic trap or a pyrotron, is a magnetic confinement fusion device that traps hot plasma between two regions of increasingly dense magnetic field, one at each end of the confinement volume, so that particles approaching either end are pushed back toward the center; because that mirror effect only works on particles within a certain range of velocity and angle, a magnetic mirror is inherently leaky and loses some particles no matter how it is built. It was one of the earliest major approaches to fusion energy, developed alongside the stellarator and the Z-pinch, but analysis by physicist Edward Teller showed the basic mirror design was fundamentally unstable, a problem Soviet researchers addressed in 1960 with a minimum-B magnetic configuration that UK researchers refined into a baseball coil design and US researchers into a yin-yang magnet layout; a later tandem mirror concept, developed at the same time in the United States and Russia, offered a possible path to a net energy positive machine without needing enormous magnets. Lawrence Livermore National Laboratory built the Mirror Fusion Test Facility, completed in 1986 at a cost of 372 million dollars, but results from the smaller Tandem Mirror Experiment exposed serious problems, and the completed facility was mothballed without ever receiving operating funds and was scrapped in 1987. Magnetic mirror research continues today in Japan and Russia, though the tokamak has become the dominant approach to fusion research.