Tandem Mirror Experiment

The Tandem Mirror Experiment (TMX and TMX-U) was a magnetic mirror machine operated from 1979 to 1987 at the Lawrence Livermore National Laboratory. The machine trapped ions and electrons between two magnetic mirrors. Ions would bounce back and forth in a line, collide in the center and fuse. This was an early experiment towards fusion power.

The design of a magnetic mirror machine was first published in 1967. The concept was developed in the US by Richard F. Post and his team at Lawrence Livermore National Laboratory during the late sixties. Partially due to the 1970s energy crisis and the Cold War the funding was available for a massive magnetic mirror and magnetic bottle research program. This led to a series of machines starting in the late 1960s and continuing into the mid eighties. This included the 2X magnetic bottle and Baseball I, Baseball II mirror machines before the TMX was built.

The TMX was formally proposed by Fred Coensgen and the Livermore team on January 12, 1977 to the US Energy Research and Development Administration. The project was projected to cost 11 million dollars. The design consisted of five rings of current around the plasma. The ends uses uniquely shaped "Baseball" magnets at the end to stop plasma from escaping. This design produced magnetic forces that increase in every direction away from the center of the mirror region. A fusion plasma shaped like a twisted bow tie is confined inside a magnetic mirror. Designing appropriate plugs was a challenge for all magnetic mirror machines. The baseball design was later replaced by the exotic yin-yang magnets of the MFTF. Problems with escaping plasma led researchers towards the Tokamak where plugs were eliminated by looping the field together.

The TMX attempted to use an "ambipolar" plasma. Ideally, this allowed it to contain electrons and ions differently. Because the ions are so much more massive than the electrons they can exist with different speeds simultaneously. Ideally, the TMX attempted to contain the ions primarily with magnetic mirrors and the slow electrons by attracting them to the trapped ions. A variation on this magnetic and electrostatic confinement is also being attempted in the Polywell.

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