HIGHLY CHARGED IONS IN RARE-EARTH PERMANENT MAGNET PENNING TRAPS

Nicholas D. Guise, Samuel M. Brewer, and Joseph N. Tan

A newly constructed apparatus at NIST is designed for the isolation, manipulation, and study of highly charged ions in a controlled environment.  Highly charged ions are produced in the NIST electron-beam ion trap (EBIT), extracted through a beamline that selects a single charge/mass species, then captured in a compact Penning trap.  The magnetic field of the Penning trap is generated by cylindrical NdFeB permanent magnets integrated into its electrodes.  Ions of charge Qe, emerging from the EBIT with energy up to 4.3Q keV, are slowed electrostatically while entering the Penning trap, then captured by pulsing closed the Penning trap front endcap voltage at the time of arrival.  Stored ions are later detected by pulsing open the back endcap to dump to a microchannel plate (MCP) detector.  We have demonstrated capture and storage of highly charged ions in two room-temperature Penning traps: (1) a prototype trap with a single NdFeB magnet, and (2) a more-elaborate trap that integrates two coaxial NdFeB magnets for improved B-field homogeneity.  Ongoing experiments utilize the two-magnet trap along with a fast time-of-flight MCP detector capable of resolving the charge-state evolution of trapped ions.  Holes in the two-magnet Penning trap ring electrode allow for optical and atomic beam access.  Demonstrated ion storage times exceed 1 second, limited primarily by background pressure of order 1 x 10^-7 Pa (~8 x 10^-10 Torr).  Potential applications include spectroscopic studies of one-electron ions in Rydberg states, as well as highly charged ions of interest in atomic physics, metrology, astrophysics, and plasma diagnostics.