New ion source dramatically improves radioactive beams for CARIBU facility

The Californium Rare Isotope Breeder Upgrade (CARIBU) just got its own upgrade. The instrument, which provides radioactive ion beams (RIB) to the Argonne ATLAS facility, now has a new Electron Beam Ion Source Charge Breeder, or EBIS-CB. The EBIS-CB improves the radioactive beam by dramatically lowering background contamination, a hindrance to the previous ion source.

“Before, only 3 percent of the beam was the desired RIB, which the scientists needed,” said co-author Richard Vondrasek. “Now with EBIS, 80 to 90 percent of the beam is the radioactive component.”

EBIS replaces the previous electron cyclotron resonance ion source (ECR-CB). While efficient, the ECR-CB had too much contamination resulting from a weakly confined plasma interacting with the chamber walls. Now with an ultrahigh vacuum system and a strongly confined electron beam, EBIS shows a reduced level of contamination.

As described in Review of Scientific Instruments, EBIS uses an electrostatic potential barrier and a strong magnetic field to trap ions from a prepared beam. Preprocessing of the beam allows the system to retain the same efficiency as with the previous ion source. Upon trapping the ions, the particles are ionized before being released in pulses. Before charge breeding radioactive isotopes, the system is tuned with a stable cesium isotope source for ease of set up.

With commissioning complete, the CARIBU-EBIS system, located at the U.S. Department of Energy’s Argonne National Laboratory, will begin conducting experiments this summer. Researchers will use the instrument to measure properties of neutron-rich nuclei usually found in stars to model the r-process path, a process thought responsible for forming about 50 percent of the heavy elements. The r-process was recently highlighted by the first detection of a gravitational wave emitted by a neutron star merger and the related observation of heavy element production.

Source: “Charge breeding of radioactive isotopes at the CARIBU facility with an electron beam ion source,” by R. C. Vondrasek, C. A. Dickerson, M. Hendricks, P. Ostroumov, R. Pardo, G. Savard, R. Scott, and G. Zinkann, Review of Scientific Instruments (2018). The article can be accessed at https://doi.org/10.1063/1.5013140 .