Sample Data During Trap Commissioning The trap electrode structure, installed in a vacuum chamber baked to 3 nT, in the bore of a superconducting solenoid, contains a long-lived electron plasma. With no applied torque to compensate, construction imperfections cause radial growth, and lost electrons are replenished through ionization of residual gas. The calibrated power input gives a measure of the confinement quality.

The following figure (7.3k gif file) shows power input (nanoWatts) versus plasma line density (number of electrons per meter). The confinement magnetic field is a parameter, varied in steps from 0.4 to 1.4 Tesla. The trapped electron column length is about 0.4 m, so the maximum number of electrons approaches 10¹⁰.

The data (left) is fairly well described by a simple two parameter model (right). One term represents radiation cooling (which competes with ionization as a sink for input power); the second term represents collective imperfection torque varying as the square of the particle number. The differing dependence on magnetic field allows these terms to be distinguished.

This "millenium plasma" was created on December 20, 1999, and is still going strong after 3.5 weeks. The trap will be opened later this month for a set of revisions and improvements.