 Following on from the earlier Baseball II device, the facility was originally a similar system in which the confinement area was located between two horseshoe-shaped "mirrors".During construction the success of the Tandem Mirror Experiment ("TMX") led to a redesign to insert a solenoid area between two such magnets, dramatically improving confinement time from a few milliseconds to over one second.Most of the fusion power would be produced in the long solenoid.