⁹⁶Zr beam production for isobar experiment in relativistic heavy ion collider

To investigate the chiral magnetic effect, ⁹⁶Zr and ⁹⁶Ru beams were accelerated at the relativistic heavy ion collider (RHIC) during Run-18 at Brookhaven National Laboratory. The ⁹⁶Zr beam was provided from the electron beam ion source (EBIS) injector, which consists of a laser ion source, an EBIS high charge state ion breeder, a 300 keV/u radio frequency quadrupole, and a 2 MeV/u interdigital H type drift tube linear accelerator (IH-DTL). The natural abundance of ⁹⁶Zr is only 2.8% with about 50% of ⁹⁰Zr. To obtain a sufficient beam current, Zr material enriched to about 60% of ⁹⁶Zr was used. The only available form of the enriched material was zirconium oxide (ZrO₂) powder, which was not well suited for a laser ion source target. We studied and established a sintering technique of the ZrO₂ powder to make a solid sample which could be installed into the laser ion source. The singly charged Zr was produced in a laser ablation plasma, extracted, and delivered to the EBIS to be ionized further to ⁹⁶Zr¹⁶⁺. We optimized the laser irradiation condition, the EBIS confinement time, and transport through the RF linacs to maximize the performance of the injector. The total number of shots provided from the laser ion source for injection into the EBIS was 489 910. The EBIS facility provided a 192 MeV stable beam of ⁹⁶Zr¹⁶⁺ ions to the booster ring of alternating gradient synchrotron (AGS) for further acceleration and stripping in the AGS/RHIC complex, allowing for successful data acquisition at the Solenoidal Tracker at the RHIC.